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| {{About|the NASA space telescope|the European cargo spacecraft|Johannes Kepler ATV|the telescope invented by Johannes Kepler|Keplerian Telescope|other uses|Kepler (disambiguation)}} | |||
| <!--{{Redirect|Kepler telescope|other uses|Keplerian Telescope}}--> | |||
| {{Use mdy dates|date=April 2014}} | |||
| {{Infobox spaceflight | |||
| | name = Kepler | |||
| <!--image of the spacecraft/mission--> | |||
| | image = Telescope-KeplerSpacecraft-20130103-717260main pia11824-full.jpg | |||
| | image_caption = Artist's impression of the ''Kepler'' telescope | |||
| | image_alt = Kepler in orbit | |||
| | image_size = 300px | |||
| <!--mission insignia or patch--> | |||
| | insignia = <!--omit the "file" prefix--> | |||
| | insignia_caption = <!--image caption--> | |||
| | insignia_alt = <!--image alt text--> | |||
| | insignia_size = <!--include px/em; defaults to 180px--> | |||
| <!--Basic details--> | |||
| | mission_type = ] | |||
| | operator = ] ] | |||
| | website = {{url|http://kepler.nasa.gov/}} | |||
| | COSPAR_ID = 2009-011A | |||
| | SATCAT = 34380 | |||
| | mission_duration = planned: 3.5 years<br/>elapsed: {{Age in years, months and days| year=2009| month=03 | day=07}} | |||
| | distance_travelled = <!-- How far the spacecraft travelled (if known) --> | |||
| | orbits_completed = <!-- number of times the spacecraft orbited the Earth - see below for spacecraft beyond Earth orbit--> | |||
| <!--Spacecraft properties--> | |||
| | spacecraft = <!--Spacecraft name/serial number (eg. Space Shuttle ''Discovery'', Apollo CM-118), etc--> | |||
| | spacecraft_type = <!--eg. GPS Block II, Kobalt-M, US-K, etc--> | |||
| | spacecraft_bus = <!--eg. A2100M, Star-2, etc--> | |||
| | manufacturer = ] | |||
| | dry_mass = {{convert|1040.7|kg|lb|abbr=on}} | |||
| | launch_mass = {{convert|1052.4|kg|lb|abbr=on}}<ref name="keplerFaq">{{cite web |url=http://kepler.nasa.gov/Mission/faq/ |title=Kepler: FAQ |publisher=] ] |accessdate=March 25, 2014}}</ref> | |||
| | payload_mass = {{convert|478|kg|lb|abbr=on}} | |||
| | dimensions = {{convert|4.7|x|2.7|m|ft|abbr=on}} | |||
| | power = 1100 watts | |||
| <!--Launch details--> | |||
| | launch_date = {{start-date|March 7, 2009, 03:49:57|timezone=yes}} UTC<ref name=kasc/> | |||
| | launch_rocket = ] (7925-10L) | |||
| | launch_site = ]<br/>] | |||
| | launch_contractor = ] | |||
| | entered_service = {{start-date|May 12, 2009, 09:01|timezone=yes}} UTC | |||
| <!--end of mission--> | |||
| | disposal_type = <!--Whether the spacecraft was deorbited, decommissioned, placed in a graveyard orbit, etc--> | |||
| | deactivated = <!-- when craft was decommissioned --> | |||
| | destroyed = <!-- when craft was destroyed (if other than by re-entry) --> | |||
| | last_contact = <!-- when last signal received if not decommissioned --> | |||
| <!-- | |||
| The following template should be used for ONE of the three above fields "end_of_mission", "decay" or "landing" if the spacecraft is no longer operational. | |||
| If it landed intact, use it for the landing time, otherwise for the date it ceased operations, or the decay date if it was still operational when it reenterd | |||
| {{end-date||timezone=yes}} UTC | |||
| or {{end-date|}} if the time is not known | |||
| --> | |||
| <!--orbit parameters--> | |||
| | orbit_epoch = <!--the date at which the orbit parameters were correct--> | |||
| | orbit_reference = ] | |||
| | orbit_regime = ]-trailing | |||
| | orbit_periapsis = <!--periapsis altitude--> | |||
| | orbit_apoapsis = <!--apoapsis altitude--> | |||
| | orbit_inclination = <!--orbital inclination--> | |||
| | orbit_semimajor = <!--semimajor axis--> | |||
| | orbit_eccentricity = <!--orbital eccentricity--> | |||
| | orbit_period = 372.5 days | |||
| | orbit_RAAN = <!--right ascension of the ascending node--> | |||
| | orbit_arg_periapsis = <!--argument of perigee/periapsis--> | |||
| | orbit_mean_anomaly = <!--mean anomaly at epoch, only use in conjunction with an epoch value--> | |||
| | orbit_mean_motion = <!--mean motion of the satellite, usually measured in orbits per day--> | |||
| | orbit_longitude = <!--geosynchronous satellites only--> | |||
| | orbit_slot = <!--Designation of orbital position or slot, if not longitude (e.g plane and position of a GPS satellite)--> | |||
| | orbit_repeat = <!--repeat interval/revisit time--> | |||
| | orbit_velocity = <!--speed at which the spacecraft was travelling at epoch - only use for spacecraft with low orbital eccentricity--> | |||
| | apsis = helion | |||
| | instruments = <!--a list of instruments on the satellite--> | |||
| <!--Telescope parameters--> | |||
| | telescope_name = <!--name, if different to the satellite--> | |||
| | telescope_type = ] | |||
| | telescope_diameter = {{convert|0.95|m|ft|abbr=on}} | |||
| | telescope_focal_length= <!--focal length of telescope--> | |||
| | telescope_area = 0.708 m<sup>2</sup>{{efn-ua|Aperture of 0.95 m yields a light-gathering area of Pi×(0.95/2)<sup>2</sup> {{=}} 0.708 m<sup>2</sup>; the 42 CCDs each sized 0.050 m × 0.025m yields a total sensor area of 0.0525 m<sup>2</sup>:<ref name="various-64714">{{cite web | url = http://www.nasa.gov/mission_pages/kepler/spacecraft/index.html | title = Kepler Spacecraft and Instrument | NASA | first = | last = Staff <!-- Verified: No author provided on page. --> | work = nasa.gov | date = June 26, 2013 | accessdate = January 18, 2014 | archiveurl = //web.archive.org/web/20140119031411/http://www.nasa.gov/mission_pages/kepler/spacecraft/index.html | archivedate = January 18, 2014 | deadurl = no}}</ref>}} | |||
| | telescope_wavelength = 400–865 nm<ref>{{cite web |author=NASA Staff | title=Kepler Mission: Photometer and Spacecraft | url=http://kepler.nasa.gov/Mission/QuickGuide/MissionDesign/PhotometerAndSpacecraft/ | publisher=] | year=2010 | accessdate=February 2, 2011 }}</ref> | |||
| | instrument_type = ] | |||
| <!--transponder parameters--> | |||
| | trans_band = ] (TT&C)<br />] (data acquisition) | |||
| | trans_frequency = <!--specific frequencies--> | |||
| | trans_bandwidth = few kbit/s (X Band)<br />~4.3 Mbit/s (K<sub>a</sub> band) | |||
| | trans_capacity = <!--capacity of the transponders--> | |||
| | trans_coverage = <!--area covered--> | |||
| | trans_TWTA = <!--TWTA output power--> | |||
| | trans_EIRP = <!--equivalent isotropic power--> | |||
| | trans_HPBW = <!--half-power beam width--> | |||
| }} | |||
| '''''Kepler''''' is a ] launched by ] to discover ] ].<ref>{{cite web |last1=Koch |first1=David | |||
| | last2=Gould | first2=Alan | title=Kepler Mission | url=http://www.kepler.arc.nasa.gov/ |publisher=] | date=March 2009 | accessdate=March 14, 2009}}</ref> The spacecraft, named after the Renaissance astronomer ],<ref>{{cite news |last=DeVore |first=Edna | title=Closing in on Extrasolar Earths | url=http://www.space.com/searchforlife/080619-seti-extrasolar-earths.html | work= |date=June 9, 2008 | accessdate=March 14, 2009}}</ref> was launched on March 7, 2009.<ref name="KeplerLaunch">{{cite web|author=NASA Staff | url=http://www.nasa.gov/mission_pages/kepler/launch/index.html | title=Kepler Launch | publisher=] |accessdate=September 18, 2009}}</ref> | |||
| Designed to survey a portion of our region of the ] to discover dozens of ] ] in or near the ] and estimate how many of the billions of stars in our galaxy have such planets,<ref>{{cite web |author=NASA Staff |title=Kepler Mission/QuickGuide |url=http://kepler.nasa.gov/Mission/QuickGuide/ |publisher=]|accessdate=April 20, 2011}}</ref><ref name="NYT-20140512">{{cite news |last=Overbye |first=Dennis |authorlink=Dennis Overbye |title=Finder of New Worlds |url=http://www.nytimes.com/2014/05/13/science/finder-of-new-worlds.html |date=12 May 2013 |work=] |accessdate=13 May 2014 }}</ref> ''Kepler's'' sole instrument is a ] that continually monitors the brightness of over 145,000 ]s in a fixed field of view.<ref>{{cite web |author=AAS Staff |title=Meeting Program and Block Schedule |url=http://aas.org/node/651 |publisher=] |accessdate=April 20, 2011}} – click the itinerary builder to get to the abstract of "Kepler Planet Detection Mission: Introduction and First Results".</ref> This data is transmitted to ], then ] periodic dimming caused by extrasolar planets that ] of their host star. | |||
| ''Kepler'' is part of NASA's ] of relatively low-cost, focused primary science missions. The telescope's construction and initial operation were managed by NASA's ], with ] responsible for developing the ''Kepler'' flight system. The ] is responsible for the ground system development, mission operations since December 2009, and science data analysis. The initial planned lifetime was 3.5 years,<ref Name="BBC7March">{{cite news |author=BBC Staff |title=Nasa launches Earth hunter probe |work=] |date=March 7, 2009 |url=http://news.bbc.co.uk/2/hi/science/nature/7926277.stm |accessdate=March 14, 2009}}</ref> but greater-than-expected noise in the data, from both the stars and the spacecraft, meant additional time was needed to fulfill all mission goals. Initially, in 2012, the mission was expected to last until 2016,<ref name="Space.com2016">. Space.com. April 4, 2012. Retrieved May 2, 2012.</ref> but this would only have been possible if all remaining ]s used for pointing the spacecraft remained reliable.<ref>{{cite news |author=Stephen Clark |title=Kepler's exoplanet survey jeopardized by two issues|publisher=Spaceflight Now |date=October 16, 2012|url=http://spaceflightnow.com/news/n1210/16kepler/ |accessdate=October 17, 2012}}</ref> On May 11, 2013, a second of four reaction wheels failed, disabling the collection of science data<ref name=prs></ref> and threatening the continuation of the mission.<ref name="nytimes.com">{{cite web |url=http://www.nytimes.com/2013/05/16/science/space/equipment-failure-may-cut-kepler-mission-short.html?_r=0 |title=Equipment Failure May Cut Kepler Mission Short |date=May 15, 2013 |accessdate=May 15, 2013}}</ref> | |||
| {{As of|2014|6}}, ''Kepler'' and its follow-up observations had found ], along with a further 3,299 unconfirmed planet candidates.{{efn-ua|This does not include Kepler candidates without a KOI designation, such as circumbinary planets, or candidates found in the Planet Hunters project.}}<ref name=wall-2013>{{cite news | url=http://www.space.com/21570-nasa-kepler-alien-planet-candidates.html | title=Ailing NASA Telescope Spots 503 New Alien Planet Candidates | work=Space.com | date=June 14, 2013 | agency=TechMediaNetwork | accessdate=June 15, 2013 | author=Wall, Mike}}</ref><ref name="NASA-ExoplanetArch">{{cite web|title=NASA's Exoplanet Archive KOI table|url=http://exoplanetarchive.ipac.caltech.edu/cgi-bin/ExoTables/nph-exotbls?dataset=cumulative|publisher=NASA|accessdate=February 28, 2014}}</ref> In November 2013, astronomers reported, based on ''Kepler'' space mission data, that there could be as many as 40 billion ] ] orbiting in the ]s of ] and ] within the ].<ref name="NYT-20131104">{{cite news |last=Overbye |first=Dennis |title=Far-Off Planets Like the Earth Dot the Galaxy |url=http://www.nytimes.com/2013/11/05/science/cosmic-census-finds-billions-of-planets-that-could-be-like-earth.html |date=November 4, 2013 |work=] |accessdate=November 5, 2013 }}</ref><ref name="PNAS-20131031">{{cite journal|last1=Petigura |first1=Eric A. |last2=Howard |first2=Andrew W. |last3=Marcy |first3=Geoffrey W. |title=Prevalence of Earth-size planets orbiting Sun-like stars|url=http://www.pnas.org/content/early/2013/10/31/1319909110 |date=October 31, 2013 |journal=]|doi=10.1073/pnas.1319909110 |accessdate=November 5, 2013 }}</ref><ref name="Space-20130107">{{cite web |title=17 Billion Earth-Size Alien Planets Inhabit Milky Way|url=http://www.space.com/19157-billions-earth-size-alien-planets-aas221.html |date=January 7, 2013 |publisher=] |accessdate=January 8, 2013 |author=Staff }}</ref> 11 billion of these estimated planets may be orbiting sun-like stars.<ref name="LATimes-20131104">{{cite news |last=Khan |first=Amina |title=Milky Way may host billions of Earth-size planets |url=http://www.latimes.com/science/la-sci-earth-like-planets-20131105,0,2673237.story |date=November 4, 2013 |work=] |accessdate=November 5, 2013 }}</ref> The nearest such planet may be 12 light-years away, according to the scientists.<ref name="NYT-20131104" /><ref name="PNAS-20131031" /> | |||
| On August 15, 2013, NASA announced that they had given up trying to fix the two failed reaction wheels. This means the current mission needs to be modified, but it does not necessarily mean the end of planet-hunting. NASA has asked the space science community to propose alternative mission plans "potentially including an exoplanet search, using the remaining two good reaction wheels and thrusters".<ref name="NASA-20130815">{{cite web |url=http://www.nasa.gov/content/nasa-ends-attempts-to-fully-recover-kepler-spacecraft-potential-new-missions-considered/ |title=NASA Ends Attempts to Fully Recover Kepler Spacecraft, Potential New Missions Considered |date=August 15, 2013 |accessdate=August 15, 2013}}</ref><ref name="NYT-20130815">{{cite news|last=Overbye |first=Dennis |title=NASA’s Kepler Mended, but May Never Fully Recover|url=http://www.nytimes.com/2013/08/16/science/space/nasas-kepler-mended-but-may-never-fully-recover.html|date=August 15, 2013 |work=] |accessdate=August 15, 2013 }}</ref><ref name="SP-20130815">{{cite web|last=Wall |first=Mike |title=Planet-Hunting Days of NASA's Kepler Spacecraft Likely Over|url=http://www.space.com/22387-nasa-planet-hunting-kepler-spacecraft-problems.html |date=August 15, 2013 |work=] |accessdate=August 15, 2013 }}</ref><ref>{{cite web|title=Kepler: NASA retires prolific telescope from planet-hunting duties|url=http://www.bbc.co.uk/news/science-environment-23724344}}</ref> On November 18, 2013, the ''K2'' (also named "Second Light") plan proposal, which may include utilizing the disabled ''Kepler'' in a way that could detect ] around smaller, dimmer ], was reported.<ref name="NYT-20131118">{{cite news |last=Overbye|first=Dennis |title=New Plan for a Disabled Kepler|url=http://www.nytimes.com/2013/11/19/science/space/new-plan-for-a-disabled-kepler.html|date=November 18, 2013 |work=] |accessdate=November 18, 2013 }}</ref><ref name="NASA-20131125" /><ref name="NASA-20131211a" /><ref name="NASA-20131211b" /> On May 16, 2014, NASA announced the approval of extending the Kepler mission to the ].<ref name="NASA-20140516">{{cite web |url=http://www.nasa.gov/content/ames/kepler-mission-manager-update-k2-has-been-approved/ |title=Kepler Mission Manager Update: K2 Has Been Approved! |work=nasa.gov |date=May 16, 2014 |publisher=] |accessdate=May 17, 2014 |others=NASA Official: Brian Dunbar; Image credit(s): NASA Ames/W. Stenzel |first=Charlie |last=Sobeck |editor1-first=Michele |editor1-last=Johnson |archiveurl=//web.archive.org/web/20140517191944/http://www.nasa.gov/content/ames/kepler-mission-manager-update-k2-has-been-approved/ |archivedate=May 17, 2014 |deadurl=no}}</ref> | |||
| ==Spacecraft== | |||
| ] | |||
| The spacecraft has a mass of {{convert|1039|kg|lb}} and contains a {{convert|1.4|m|in|0|adj=on|sp=us}} ] feeding an ] of {{convert|0.95|m|in|1|adj=on|sp=us}} – at the time of its launch this was the largest mirror on any telescope outside Earth orbit.<ref>{{cite web |last=Atkins |first=William |title=Exoplanet Search Begins with French Launch of Corot Telescope Satellite |url=http://www.itwire.com/content/view/8299/1066/ |publisher=iTWire |date=December 28, 2008 |accessdate=May 6, 2009}}</ref> The spacecraft has a 115 deg<sup>2</sup> (about 12-degree diameter) ] (FOV), roughly equivalent to the size of one's fist held at arm's length. Of this, 105 deg<sup>2</sup> is of science quality, with less than 11% ]. The photometer has a ] to provide excellent ], rather than sharp images. The mission goal is a combined differential photometric precision (CDPP) of 20 ppm for a ''m''(V)=12 solar-like star for a 6.5-hour integration, though the observations so far have fallen short of this objective (see ]). An Earth-like transit produces a brightness change of 84 ppm and lasts for thirteen hours when it crosses the center of the star. | |||
| ===Camera=== | |||
| ].]] The focal plane of the spacecraft's camera is made up of 42 ] at 2200x1024 ]s, which made it at the time the largest camera yet launched into space, possessing a total resolution of 95 ].<ref>{{cite web |author=NASA Staff |title=Kepler: Spacecraft and Instrument |url=http://www.nasa.gov/mission_pages/kepler/spacecraft/index.html |publisher=] |accessdate=May 1, 2009}}</ref><ref>{{cite web |author=NASA Staff |title=Kepler's Diamond Mine of Stars |url=http://www.nasa.gov/mission_pages/kepler/multimedia/images/fullFFINoCalloutsHot300.html |publisher=] |date=April 16, 2009 |accessdate=May 1, 2009}}</ref> The array is cooled by heat pipes connected to an external radiator.<ref name=presskit>{{cite journal |author=NASA Staff |url=http://www.nasa.gov/pdf/314125main_Kepler_presskit_2-19_smfile.pdf |title=Kepler: NASA's First Mission Capable of Finding Earth-Size Planets |publisher=] |date=February 2009 |accessdate=March 14, 2009}}</ref> The CCDs are read out every six seconds (to limit saturation) and co-added on board for 58.89 seconds for short cadence targets, and 1765.5 seconds (29.4 minutes) for long cadence targets. Due to the larger bandwidth requirements for the former, these are limited in number to 512 compared to ~160,000 for long cadence. However, even though at launch ''Kepler'' had the highest data rate of any NASA mission, the 29-minute sums of all 95 million pixels constitute more data than can be stored and sent back to Earth. Therefore the science team has pre-selected the relevant pixels associated with each star of interest, amounting to about 6 percent of the pixels (5.4 megapixels). The data from these pixels is then requantized, compressed and stored, along with other auxiliary data, in the on-board 16 gigabyte solid-state recorder. Data that is stored and downlinked includes science stars, ]s, smear, black level, background and full field-of-view images.<ref name="presskit"/><ref>{{cite web |title=PyKE Primer - 2. Data Resources |url=http://keplergo.arc.nasa.gov/PyKEprimerResources.shtml |publisher=] |accessdate=March 12, 2014}}</ref> | |||
| ===Primary mirror=== | |||
| ] | |||
| The ''Kepler'' primary mirror is {{convert|1.4|m|ft|sp=us}} in diameter, the largest mirror located outside Earth orbit. Manufactured by glass maker ] using ], the mirror is specifically designed to have a mass only 14% that of a solid mirror of the same size.<ref>{{cite web |title=Kepler Primary Mirror |url=http://www.nasa.gov/mission_pages/kepler/multimedia/images/PMA_backside_inspection_1_at_SOC.html |publisher=NASA |accessdate=April 5, 2013}}</ref><ref>{{cite web |title=Corning To Build Primary Mirror For Kepler Photometer |url=http://www.spacedaily.com/news/extrasolar-03q.html |accessdate=April 5, 2013}}</ref> In order to produce a space telescope system with sufficient sensitivity to detect relatively small planets, as they pass in front of stars, a very high reflectance coating on the primary mirror was required. Using ], ] applied a protective 9-layer silver coating to enhance reflection and a dielectric interference coating to minimize the formation of color centers and atmospheric moisture absorption.<ref>{{cite journal |last1=Fulton L. |first1=Michael |last2=Dummer |first2=Richard S. |year=2011 |title= Advanced Large Area Deposition Technology for Astronomical and Space Applications |journal= Vacuum & Coating Technology |volume= |issue=December 2011 |pages=43–47 |publisher= |doi= |url= http://e-ditionsbyfry.com/Olive/ODE/VTC/Default.aspx?href=VTC/2011/12/01 | |||
| |accessdate=April 6, 2013}}</ref><ref>{{cite web |url=http://www.spaceref.com/news/viewpr.html?pid=23610 |title=Ball Aerospace Completes Primary Mirror and Detector Array Assembly Milestones for Kepler Mission |last1= |first1=Ball Aerospace and Technologies Corp. |last2= |first2= |date=September 25, 2007 |work= |publisher=spaceref.com |accessdate=April 6, 2013}}</ref> | |||
| ===Performance=== | |||
| In terms of photometric performance, ''Kepler'' is working well,{{when|date=August 2013}} much better than any Earth-bound telescope, but still short of the design goals. The objective was a combined differential photometric precision (CDPP) of 20 parts per million (PPM) on a magnitude 12 star for a 6.5 hour integration. This estimate was developed allowing 10 ppm for stellar variability, roughly the value for the Sun. The obtained accuracy for this observation has a wide range, depending on the star and position on the focal plane, with a median of 29 ppm. Most of the additional noise appears to be due to a larger-than-expected variability in the stars themselves (19.5 ppm as opposed to the assumed 10.0 ppm), with the rest due to instrumental noise sources slightly larger than predicted.<ref>{{cite arXiv |last1=Gilliland |first1=Ronald L. |coauthors=''et al.'' |year=2011 |title= Kepler Mission Stellar and Instrument Noise Properties|class= astro-ph.SR|eprint=1107.5207}}</ref> Work is ongoing{{when|date=August 2013}} to better understand, and perhaps calibrate out, instrument noise.<ref>{{cite journal |first1=Douglas A. |last1=Caldwell |first2=Jeffrey E. |last2=van Cleve |first3=Jon M. |last3=Jenkins |first4=Vic S. |last4=Argabright |first5=Jeffery J. |last5=Kolodziejczak |first6=Edward W. |last6=Dunham |first7=John C. |last7=Geary |first8=Peter |last8=Tenenbaum |first9=Hema |last9=Chandrasekaran |first10=Jie |last10=Li |first11=Hayley |last11=Wu |first12=Jason |last12=von Wilpert |year=2010 |title=Kepler Instrument Performance: An In-Flight Update |journal=] |volume=7731 |page=30 |url=http://kepler.nasa.gov/Science/ForScientists/papersAndDocumentation/SOCpapers/spie_2010_instrument_char_web_version.pdf |doi=10.1117/12.856638 |bibcode=2010SPIE.7731E..30C |series=Space Telescopes and Instrumentation 2010: Optical, Infrared, and Millimeter Wave |publisher=International Society for Optics and Photonics |editor1-last=Oschmann, Jr |editor1-first=Jacobus M |editor2-last=Clampin |editor2-first=Mark C |editor3-last=MacEwen |editor3-first=Howard A}}</ref> | |||
| Since the signal from an Earth-size planet is so close to the noise level (only 80 ppm), the increased noise means each individual transit is only a 2.7 σ event, instead of the intended 4 σ. This, in turn, means more transits must be observed to be sure of a detection. Scientific estimates indicated that a 7–8-year mission, as opposed to the originally planned 3.5 years, would be needed to find all transiting Earth-sized planets.<ref name="SandT">{{cite web |url=http://www.skyandtelescope.com/news/126242378.html |title=Kepler's Dilemma: Not Enough Time |publisher=Sky and Telescope |author=Kelly Beatty |date=September 2011}}</ref> On April 4, 2012, the ''Kepler'' mission was approved for extension through the fiscal year 2016,<ref name=Space.com2016/><ref name="mission extension">{{cite web |url=http://kepler.nasa.gov/news/index.cfm?FuseAction=ShowNews&NewsID=199 |title=NASA Approves Kepler Mission Extension |publisher=kepler.nasa.gov |author=News |date=April 4, 2012}}</ref> but this also depended on all remaining reaction wheels staying healthy, which turned out not to be the case (see ] below). | |||
| ===Spacecraft orbit and orientation=== | |||
| ] | |||
| ], ] and ].]] | |||
| ''Kepler'' ],<ref name="keplerlaunch1"/><ref>{{cite web |last1=Koch |first1=David |last2=Gould |first2=Alan |title=Kepler Mission: Launch Vehicle and Orbit |url=http://kepler.nasa.gov/sci/design/orbit.html |archiveurl=http://web.archive.org/web/20070622161529/http://kepler.nasa.gov/sci/design/orbit.html |archivedate=June 22, 2007 |publisher=] |date=March 2009 | accessdate=March 14, 2009}}</ref> which avoids Earth occultations, stray light, and ] perturbations and ]s inherent in an Earth orbit. The ] points to a field in the ] ]s of ], ] and ], which is well out of the ] plane, so that sunlight never enters the photometer as the spacecraft orbits the Sun. (] objects and the ] do not obscure the field of view.<ref name=presskit/>) | |||
| This is also the direction of the Solar System's motion around the center of the galaxy. Thus, the stars which ''Kepler'' observes are roughly the same distance from the galactic center as the ], and also close to the galactic plane. This fact is important if position in the galaxy is related to habitability, as suggested by the ]. | |||
| NASA has characterised ''Kepler'''s orbit as "Earth-trailing".<ref>{{cite web|url=http://www.nasa.gov/mission_pages/kepler/spacecraft/index-mission.html |title=Kepler: Spacecraft and Instrument |publisher=NASA |accessdate=December 21, 2011}}</ref> With an orbital period of 372.5 days, ''Kepler'' slowly falls further behind Earth. | |||
| ===Spacecraft operations=== | |||
| ]s and ]es.]] | |||
| ''Kepler'' is operated out of ], by the Laboratory for Atmospheric and Space Physics (]) under contract to Ball Aerospace & Technologies Corp. The spacecraft's solar array is rotated to face the Sun at the ]s and ]es, so as to optimize the amount of sunlight falling on the solar array and to keep the heat radiator pointing towards deep space.<ref name=presskit/> Together, LASP and Ball Aerospace control the spacecraft from a mission operations center located on the research campus of the ]. LASP performs essential mission planning and the initial collection and distribution of the science data. The mission's initial life-cycle cost was estimated at US$600 million, including funding for 3.5 years of operation.<ref name=presskit/> In 2012, NASA announced that the ''Kepler'' mission would be funded until 2016.<ref name=Space.com2016/> | |||
| ====Communications==== | |||
| NASA contacts the spacecraft using the ] communication link twice a week for command and status updates. Scientific data are downloaded once a month using the ] link at a maximum data transfer rate of approximately 550 KBps. The ''Kepler'' spacecraft conducts its own partial analysis on board and only transmits scientific data deemed necessary to the mission in order to conserve bandwidth.<ref>{{cite news |last=Ng |first=Jansen | url=http://www.dailytech.com/Kepler+Mission+Sets+Out+to+Find+Planets+Using+CCD+Cameras/article14421.htm |title=Kepler Mission Sets Out to Find Planets Using CCD Cameras | work=DailyTech |date=March 8, 2009 |accessdate=March 14, 2009}}</ref> | |||
| ====Data management==== | |||
| Science data telemetry collected during mission operations at LASP is sent for processing to the ''Kepler'' Data Management Center (DMC) which is located at the ] on the campus of ] in ]. The science data telemetry is decoded and processed into uncalibrated ]-format science data products by the DMC, which are then passed along to the Science Operations Center (SOC) at NASA Ames Research Center, for calibration and final processing. The SOC at NASA Ames Research Center (ARC) develops and operates the tools needed to process scientific data for use by the ''Kepler'' Science Office (SO). Accordingly, the SOC develops the pipeline data processing software based on scientific algorithms developed by the SO. During operations, the SOC: | |||
| #Receives calibrated pixel data from the DMC | |||
| #Applies the analysis algorithms to produce light curves for each star | |||
| #Performs transit searches for detection of planets (threshold-crossing events, or TCEs) | |||
| #Performs data validation of candidate planets by evaluating various data products for consistency as a way to eliminate false positive detections | |||
| The SOC also evaluates the photometric performance on an on-going basis and provides the performance metrics to the SO and Mission Management Office. Finally, the SOC develops and maintains the project’s scientific databases, including catalogs and processed data. The SOC finally returns calibrated data products and scientific results back to the DMC for long-term archiving, and distribution to astronomers around the world through the Multimission Archive at STScI (MAST). | |||
| ===Spacecraft history=== | |||
| In January 2006, the project's launch was delayed eight months because of budget cuts and consolidation at NASA.<ref name="MissionHistory">{{cite web |last=Borucki |first=W. J. |date=May 22, 2010 |url=http://kepler.nasa.gov/Mission/QuickGuide/history/ |title=Brief History of the Kepler Mission |publisher=] |accessdate=April 23, 2011}}</ref> It was delayed again by four months in March 2006 due to fiscal problems.<ref name="MissionHistory"/> At this time, the ] was changed from a ]-led design to one fixed to the frame of the spacecraft to reduce cost and complexity, at the cost of one observation day per month. | |||
| ] | |||
| The ''Kepler'' observatory was launched on March 7, 2009 at 03:49:57 UTC aboard a ] from ], Florida.<ref name="kasc">{{cite web |author=Aarhus University Staff |title=KASC Scientific Webpage | url=http://astro.phys.au.dk/KASC/ |publisher= |date=March 14, 2009 |accessdate=March 14, 2009}}</ref><ref name="KeplerLaunch"/> The launch was a complete success and all three stages were completed by 04:55 UTC. The cover of the telescope was jettisoned on April 7, 2009, and the ] images were taken on the next day.<ref>{{cite web |last=DeVore |first=Edna |url=http://www.space.com/searchforlife/090409-kepler-dust-cover.html |title=Planet-Hunting Kepler Telescope Lifts Its Lid |date=April 9, 2009 |publisher= |accessdate=April 14, 2009}}</ref><ref>{{cite web |author=NASA Staff |url=http://www.nasa.gov/home/hqnews/2009/apr/HQ_09-085_Kepler_First_Light.html|title=NASA's Kepler Captures First Views of Planet-Hunting Territory |date=April 16, 2009 |publisher=]|accessdate=April 16, 2009}}</ref> | |||
| On April 20, 2009, it was announced that the ''Kepler'' science team had concluded that further refinement of the focus would dramatically increase the scientific return.<ref>{{cite web |author=NASA Staff |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090420.html |title=04.20.09 – Kepler Mission Manager Update |date=April 20, 2009 |publisher=] |accessdate=April 20, 2009}}</ref> On April 23, 2009, it was announced that the focus had been successfully optimized by moving the primary mirror 40 ] (1.6 thousandths of an inch) towards the focal plane and tilting the primary mirror 0.0072 degree.<ref>{{cite web |author=NASA Staff |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090424.html |title=04.23.09 – Kepler Mission Manager Update |date=April 23, 2009 |publisher=] |accessdate=April 27, 2009}}</ref> | |||
| On May 12, 2009, at 17:01 ], ''Kepler'' successfully completed its commissioning phase and began its search for planets around other stars.<ref name="Update20090514">{{cite web |author=NASA Staff | url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090514.html |title=05.14.09 – Kepler Mission Manager Update |date=May 14, 2009 |publisher=] |accessdate=May 16, 2009}}</ref><ref>{{cite web | author=NASA Staff |title=Let the Planet Hunt Begin | url=http://www.nasa.gov/mission_pages/kepler/news/kepler-200905013.html | publisher=] |date=May 13, 2009 |accessdate=May 13, 2009}}</ref> | |||
| ] | |||
| On June 19, 2009, the spacecraft successfully sent its first science data to Earth. It was discovered that ''Kepler'' had entered ] on June 15. A second safe mode event occurred on July 2. In both cases the event was triggered by a ''processor reset''. The spacecraft resumed normal operation on July 3 and the science data that had been collected since June 19 was downlinked that day.<ref name="Update20090707">{{cite web |author=NASA Staff |url=http://kepler.nasa.gov/Mission/mmupdates/missionManagerArchive/ |title=2009 July 7 Mission Manager Update |date=July 7, 2009 |publisher=] |accessdate=April 23, 2011}}</ref> On October 14, 2009, the cause of these safing events was determined to be a ] power supply that provides power to the ] processor.<ref name="Update20091014">{{cite web |author=NASA Staff|url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20091014.html |title=Kepler Mission Manager Update |date=October 14, 2009 |publisher=] |accessdate=October 18, 2009}}</ref> On January 12, 2010, one portion of the focal plane transmitted anomalous data, suggesting a problem with focal plane MOD-3 module, covering two out of ''Kepler'''s 42 ]. {{As of|2010|10}}, the module was described as "failed", but the coverage still exceeded the science goals.<ref>{{cite web |author=NASA Staff |title=Kepler outlook positive; Followup Observing Program in full swing |url=http://kepler.nasa.gov/news/mmu/index.cfm?FuseAction=ShowNews&NewsID=55 |date=August 23, 2010 |accessdate=April 23, 2011}}</ref> | |||
| ''Kepler'' downlinked roughly twelve ]s of data<ref name="Update20090923">{{cite web |author=NASA Staff |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20090923.html |title=Kepler Mission Manager Update |date=September 23, 2009 |publisher=] |accessdate=September 25, 2009}}</ref> about once per month<ref name="Update20091105">{{cite web |author=NASA Staff |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20091105.html |title=Kepler Mission Manager Update |date=November 5, 2009 |publisher=] |accessdate=November 8, 2009 }}</ref>—an example of such a downlink was on November 22–23, 2010.<ref>{{cite web |author=NASA Staff |title=Data Download; Data Release; 2010 ground-based observing complete; AAS meeting |url=http://kepler.nasa.gov/news/mmu/index.cfm?FuseAction=ShowNews&NewsID=83 |date=December 6, 2010 |accessdate=December 21, 2010 }}</ref> | |||
| On July 14, 2012, one of the four ]s used for fine pointing of the spacecraft failed.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20122407.html |title=Kepler Mission Manager Update |date=July 24, 2012 |author=Roger Hunter |publisher=NASA}}</ref> While Kepler requires only three reaction wheels to accurately aim the telescope, another failure would leave the spacecraft unable to continue in its mission. This is a potential threat to the extended mission.<ref>{{cite web |title=Kepler glitch may lower odds of finding Earth's twin |date=July 24, 2012 |author=Maggie McKee |publisher=New Scientist |url=http://www.newscientist.com/article/dn22096-kepler-glitch-may-lower-odds-of-finding-earths-twin.html}}</ref> | |||
| On January 17, 2013, NASA announced that one of the three remaining reaction wheels showed increased friction, and that ''Kepler'' would discontinue operation for ten days as a possible way of solving the problem. If this second wheel should also fail, the ''Kepler'' mission would be over.<ref name="NASA-20130117">{{cite web |last=Hunter |first=Roger |title=Kepler Mission Manager Update |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130117.html |date=January 17, 2013 |publisher=] |accessdate=January 18, 2013 }}</ref><ref name="Marchis-20130117">{{cite web |last=Marchis |first=Franck |title=Kepler is Sick and Resting: 'Mountain View, we have a problem' |url=http://cosmicdiary.org/fmarchis/2013/01/17/kepler-is-damaged-and-now-resting-mountain-view-we-have-a-problem/ |date=January 17, 2013 |publisher=Cosmic Diary |accessdate=January 18, 2013 }}</ref> On January 29, 2013, NASA reported the successful return to normal science collection mode,<ref name="NASA-20130129">{{cite web |last=Hunter |first=Roger | |||
| |title=Kepler Mission Manager Update: Kepler Returns to Science Mode |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20132901.html |date=January 29, 2013 |publisher=] |accessdate=January 30, 2013 }}</ref> though the reaction wheel still exhibits elevated and erratic friction levels.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130329.html |title=Kepler Mission Manager Update, 29.03.2013 |author=Roger Hunter |publisher=NASA}}</ref> | |||
| On May 11, 2013, another reaction wheel failed and the spacecraft was put in 'Point Rest State' by May 15, 2013.<ref name=prs/> In PRS, the spacecraft uses a combination of thrusters and solar pressure to control pointing.<ref name=prs/> The fuel use is low, which allows time to attempt recovery of the spacecraft.<ref name=prs/> | |||
| <!-- | |||
| On May 15, 2013, a newspaper reported that NASA was planning to announce that the reaction wheel that had previously shown abnormal activity had failed.<ref name="nytimes.com"/> Unnamed astronomers reiterated that should repairs not be possible, the Kepler mission would be terminated. --> | |||
| The spacecraft automatically went into a thruster-controlled safe mode with the solar panels facing the Sun and with an intermittent communication link with the Earth. In this state the fuel would last for several months. Commands were sent to the spacecraft to put it into Point Rest State. This state reduced fuel consumption - fuel reserves would last for several years in this state. This state also makes communication possible at any time. Work was started on the possibility of getting at least one reaction wheel working again.<ref>{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130515.html |title=Kepler Mission Manager Update |date=May 15, 2013 |publisher=NASA |accessdate=June 14, 2013}}</ref><ref>{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130521.html |title=Kepler Mission Manager Update |date=May 21, 2013 |publisher=NASA |accessdate=June 14, 2013}}</ref> | |||
| In July 2013, the spacecraft remained in "point rest state" while recovery efforts were planned.<ref name=recovery></ref> By August 15, 2013, attempts to resolve issues with two of the four reaction wheels failed.<ref name="NASA-20130815" /><ref name="NYT-20130815" /><ref name="SP-20130815" /> An engineering report was ordered to assess the spacecraft's remaining capabilities.<ref name="NASA-20130815" /> | |||
| ==Field of view== | |||
| ].]] | |||
| <!--- | |||
| The image, shown to the right, is magnified detail from the full field of view image shown above. This image also identifies the ] system and clearly shows the parent ], ], in the ] ]. | |||
| ---> | |||
| ''Kepler'' has a fixed ] (FOV) against the sky. The diagram to the right shows the ] and where the detector fields are located, along with the locations of a few bright stars with ] at the top left corner. The mission website has a that will determine if a given object falls in the FOV, and if so, where it will appear in the photo detector output data stream. Data on extrasolar planet candidates is submitted to the ], or KFOP, to conduct follow-up observations. | |||
| ''Kepler'''s field of view covers 100 ]s, around 0.25 percent of the sky, or "about two scoops of the Big Dipper". Thus, it would require around 400 ''Kepler''-like telescopes to cover the whole sky.<ref>{{cite web |author=Ball Aerospace & Technologies |url=http://www.ballaerospace.com/page.jsp?page=186 |title=Kepler mission & program information|publisher=] |accessdate=September 18, 2012}}</ref> | |||
| ==Objectives and methods== | |||
| The scientific objective of ''Kepler'' is to explore the structure and diversity of ].<ref>{{cite web |last1=Koch |first1=David |last2=Gould |first2=Alan |title=Overview of the Kepler Mission | url=http://www.cfa.harvard.edu/kepler/papers/2004/SPIE.Glasgow.Koch.pdf | publisher=SPIE |year=2004 |accessdate=December 9, 2010}}</ref> This spacecraft observes a large sample of stars to achieve several key goals: | |||
| * To determine how many Earth-size and larger planets there are in or near the ] (often called "]s")<ref name="Muir">{{cite news |last1=Muir |first1=Hazel |url=http://www.newscientist.com/article/dn11710 |title= 'Goldilocks' planet may be just right for life |work=] |date=April 25, 2007 |accessdate=April 2, 2009 }}</ref> of a wide variety of spectral types of stars. | |||
| * To determine the range of size and shape of the orbits of these planets. | |||
| * To estimate how many planets there are in multiple-star systems. | |||
| * To determine the range of orbit size, brightness, size, mass and density of short-period giant planets. | |||
| * To identify additional members of each discovered planetary system using other techniques. | |||
| * Determine the properties of those stars that harbor planetary systems. | |||
| Most of the ]s previously detected by other projects were ]s, mostly the size of ] and bigger. ''Kepler'' is designed to look for planets 30 to 600 times less massive, closer to the order of Earth's mass (Jupiter is 318 times more massive than Earth). The method used, the ], involves observing repeated ] of planets in front of their stars, which causes a slight reduction in the star's ], on the order of 0.01% for an Earth-size planet. The degree of this reduction in brightness can be used to deduce the diameter of the planet, and the interval between transits can be used to deduce the planet's orbital period, from which estimates of its orbital ] (using ]) and its temperature (using models of stellar radiation) can be calculated. | |||
| The ] of a ] ] being along the line-of-sight to a star is the diameter of the star divided by the diameter of the orbit.<ref name="geomprob">{{cite web |others=Curators: David Koch, Alan Gould| title=Kepler Mission: Characteristics of Transits (section "Geometric Probability") | url=http://kepler.nasa.gov/sci/basis/character.html | publisher=NASA | date=March 2009 | accessdate=September 21, 2009|archiveurl=http://web.archive.org/web/20090825002919/http://kepler.nasa.gov/sci/basis/character.html|archivedate=August 25, 2009|deadurl=yes}}</ref> For an Earth-like planet at 1 ] transiting a Sol-like star the probability is 0.47%, or about 1 in 210.<ref name="geomprob"/>{{efn-ua|This probability only has two significant figures. Thus, it is stated as 1 in 210, not 1 in 212.77}} For a planet like Venus orbiting a Sol-like star the probability is slightly higher, at 0.65%;<ref name="geomprob"/> such planets could be Earth-like if the host star is a ] such as ].{{citation needed|date=February 2014}} If the host star has multiple planets, the probability of additional detections is higher than the probability of initial detection assuming planets in a given system tend to orbit in similar planes – an assumption consistent with current models of planetary system formation.<ref name="geomprob"/> For instance, if a ''Kepler''-like mission conducted by aliens observed Earth transiting the Sun, there is a 12% chance that it would also see ] transiting.<ref name="geomprob"/> | |||
| ''Kepler''<nowiki>'</nowiki>s 115-deg<sup>2</sup> field of view gives it a much higher probability of detecting Earth-like planets than the ], which has a field of view of only ]. Moreover, ''Kepler'' is dedicated to detecting planetary transits, while the Hubble Space Telescope is used to address a wide range of scientific questions, and rarely looks continuously at just one starfield. Of the approximately half-million stars in ''Kepler'''s field of view, around 150,000 stars were selected for observation. More than 90,000 are G-type stars on, or near, the ]. Thus, Kepler was designed to be sensitive to wavelengths of 400–865 nm where brightness of those stars peaks. Most of the stars observed by Kepler are have apparent visual magnitude of >14 but the brightest observed stars have visual magnitude of 8 or lower. Most of the candidates were initially not expected to be confirmed due to being too faint for follow-up observations.<ref name="arXiv-1001.0349v1">{{cite journal |url=http://arxiv.org/pdf/1001.0349 |title=Selection, Prioritization, and Characteristics of Kepler Target Stars |date=January 3, 2010 |publisher=] |location=] |accessdate=March 3, 2014 |format=PDF |arxiv=1001.0349v1 |journal= |first1=N. M. |last1=Batalha |first2=W. J. |last2=Borucki |first3=D. G. |last3=Koch |first4=S. T. |last4=Bryson |first5=M. R. |last5=Haas |first6=T. M. |last6=Brown |first7=D. A. |last7=Caldwell |first8=R. L. |last8=Gilliland |first9=D. W. |last9=Latham |first10=S. |last10=Meibom |first11=D. G. |last11=Monet}}</ref> All the selected stars are observed simultaneously, with the spacecraft measuring variations in their brightness every thirty minutes. This provides a better chance for seeing a transit. The mission was designed to maximize the probability of detecting planets orbiting other stars.<ref name=presskit /><ref name="mission_faq">{{cite web |others=Curators: David Koch, Alan Gould|title=Kepler Mission: Frequently Asked Questions |url=http://kepler.nasa.gov/about/faq.html | archiveurl=http://web.archive.org/web/20070820000813/http://kepler.nasa.gov/about/faq.html |archivedate=August 20, 2007 |publisher=] |date=March 2009 | accessdate=March 14, 2009 }}</ref> | |||
| Since ''Kepler'' must observe at least three transits to confirm that the dimming of a star was caused by a transiting planet, and since larger planets give a signal that is easier to check, scientists expected the first reported results to be larger Jupiter-size planets in tight orbits. The first of these were reported after only a few months of operation. Smaller planets, and planets farther from their sun would take longer, and discovering planets comparable to Earth were expected to take three years or longer.<ref name="keplerlaunch1">{{cite press release |author=NASA Staff |title=Kepler Mission Rockets to Space in Search of Other Earth | url=http://science.nasa.gov/headlines/y2009/06mar_keplerlaunch.htm?friend |publisher=] |date=March 6, 2009 |accessdate=March 14, 2009 }}</ref> | |||
| Data collected by ''Kepler'' is also being used for studying ] of various types and performing ],<ref>{{cite arXiv |last1=Grigahcène |first1=A. |coauthors=''et al.'' |year=2010 |title=Hybrid γ Doradus – δ Scuti pulsators: New insights into the physics of the oscillations from ''Kepler'' observations |class=astro-ph.SR |eprint=1001.0747}}</ref> particularly on stars showing ].<ref>{{cite arXiv |last1=Chaplin |first1=W. J. |coauthors=''et al.'' |year=2010 |title=The asteroseismic potential of ''Kepler'': first results for solar-type stars |class=astro-ph.SR |eprint=1001.0506 }}</ref> | |||
| ==Planet finding process== | |||
| ===Finding planet candidates=== | |||
| Once Kepler has collected and sent back the data, raw light curves are constructed. The next step is processing (folding) light curves into more easily observable form and letting software to select signals that seem potentially transit-like. At this point, any signal that shows potential transit-like features is called threshold crossing event. These signals are individually inspected in 2 inspection rounds with the first round taking only a few seconds per target. This inspection eliminates erroneously selected non-signals, signals caused by instrumental noise and obvious eclipsing binaries. <ref>http://exoplanetarchive.ipac.caltech.edu/docs/PurposeOfKOITable.html</ref> | |||
| Threshold crossing events that pass these tests are now called Kepler Objects of Interest (KOI), receive a KOI designation and are archived. KOIs are inspected more thoroughly in a process called dispositioning. Those which pass the dispositioning are called Kepler planet candidates. The KOI archive is not static, meaning that a Kepler candidate could end up in the false-positive list upon further inspection. In turn, KOIs that were mistakenly classified as false positives could end up back in the candidates list.<ref name="C4WDefault-7178839">{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-new-data-q-and-a.html#.U1M_k1feiIY |title=New NASA Kepler Mission Data |work=nasa.gov |date=May 31, 2013 |publisher=] |others=NASA Official: Brian Dunbar; Image credit: NASA Ames/W. Stenzel |accessdate=April 20, 2014 |type=Interview |first=Michael |last=Haas |archiveurl=//web.archive.org/web/20140420090621/http://www.nasa.gov/mission_pages/kepler/news/kepler-new-data-q-and-a.html |archivedate=April 20, 2014 |deadurl=no}}</ref> | |||
| Not all the planet candidates go through this process. Circumbinary planets do not show strictly periodic transits, and have to be inspected through other methods. In addition, third-party researchers use different data-processing methods, or even search planet candidates from the unprocessed light curve data. As a consequence, those planets may be missing KOI designation. | |||
| ===Confirming planet candidates=== | |||
| Once suitable candidates have been found from Kepler data, it is necessary to rule out false positives with follow-up tests. | |||
| Usually, Kepler candidates are imaged individually with more-advanced ground-based telescopes in order to resolve any background objects which could contaminate the brightness signature of the transit signal.<ref>{{cite arXiv |last1=Batalha |first1=Natalie M. |coauthors=''et al.'' |year=2010 |title=Pre-Spectroscopic False Positive Elimination of Kepler Planet Candidates |class=astro-ph.EP |eprint=1001.0392}}</ref> Another method to rule out planet candidates is ] for which ''Kepler'' can collect good data even though doing so was not a design goal. While Kepler cannot detect planetary-mass objects with this method, it can be used to determine if the transit was caused by a stellar-mass object.<ref>{{cite arXiv |last1=Monet |first1=David G. |coauthors=''et al.'' |year=2010 |title=Preliminary Astrometric Results from Kepler |class=astro-ph.IM |eprint=1001.0305}}</ref> | |||
| ====Through other detection methods==== | |||
| There are a few different exoplanet detection methods which help to rule out false positives by giving further proof that a candidate is a real planet. One of the methods, called ], requires follow-up observations from ground-based telescopes. This method works well if the planet is massive or is located around a relatively bright star. While current spectrographs are insufficient for confirming planetary candidates with small masses around relatively dim stars, this method can be used to discover additional massive non-transiting planet candidates around targeted stars. | |||
| In multiplanetary systems, planets can often be confirmed through ] by looking at the time between successive transits, which may vary if planets are gravitationally perturbed by each other. This helps to confirm relatively low-mass planets even when the star is relatively distant. Transit timing variations indicate that two or more planets belong to the same planetary system. There are even cases where a non-transiting planet is also discovered in this way.<ref></ref> | |||
| ]s show much larger transit timing variations between transits than planets gravitationally disturbed by other planets. Their transit duration times also vary significantly. Transit timing and duration variations for circumbinary planets are caused by the orbital motion of the host stars, rather than by other planets.<ref>{{cite arXiv |eprint=1009.5905 |author1=Nascimbeni |author2=Piotto |author3=Bedin |author4=Damasso |title=TASTE: The Asiago Survey for Timing transit variations of Exoplanets |class=astro-ph.EP |year=2008}}</ref> In addition, if the planet is massive enough, it can cause slight variations of the host stars' orbital periods. Despite being harder to find circumbinary planets due to their non-periodic transits, it is much easier to confirm them, as timing patterns of transits cannot be mimicked by an eclipsing binary or a background star system.<ref></ref> | |||
| In addition to transits, planets orbiting around their stars undergo reflected-light variations – like the ], they go through ] from full to new and back again. Since ''Kepler'' cannot resolve the planet from the star, it sees only the combined light, and the brightness of the host star seems to change over each orbit in a periodic manner. Although the effect is small – the photometric precision required to see a close-in giant planet is about the same as to detect an Earth-sized planet in transit across a solar-type star – Jupiter-sized planets with an orbital period of a few days or less are detectable by sensitive space telescopes such as ''Kepler''. In the long run, this method may help find more planets than the transit method, because the reflected light variation with orbital phase is largely independent of the planet's orbital inclination, and does not require the planet to pass in front of the disk of the star. In addition, the phase function of a giant planet is also a function of its thermal properties and atmosphere, if any. Therefore, the phase curve may constrain other planetary properties, such as the particle size distribution of the atmospheric particles.<ref>{{cite journal|last=Jenkins|first=J.M.|author2=Laurance R. Doyle |date=September 20, 2003|title=Detecting reflected light from close-in giant planets using space-based photometers|journal=Astrophysical Journal|volume=1|issue=595|pages=429–445|doi=10.1086/377165|url = http://www.iop.org/EJ/article/0004-637X/595/1/429/56774.web.pdf|format = ]|bibcode=2003ApJ...595..429J|arxiv = astro-ph/0305473 }}</ref> | |||
| Kepler's photometric precision is often high enough to observe a star's brightness changes caused by ] or a star's shape deformation by a companion. These can sometimes be used to rule out hot Jupiter candidates as false positives caused by a star or a brown dwarf when these effects are too noticeable.<ref name="arXiv-1402.6534v1">{{cite journal |url=http://arxiv.org/pdf/1402.6534 |title=Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems |date=February 26, 2014 |publisher=] |location=] |accessdate=March 2, 2014 |format=PDF |arxiv=1402.6534v1 |journal= |first1=Jason F. |last1=Rowe |first2=Stephen T. |last2=Bryson |first3=Geoffrey W. |last3=Marcy |first4=Jack J. |last4=Lissauer |first5=Daniel |last5=Jontof-Hutter |first6=Fergal |last6=Mullally |first7=Ronald L. |last7=Gilliland |first8=Howard |last8=Issacson |first9=Eric |last9=Ford |first10=Steve B. |last10=Howell |first11=William J. |last11=Borucki |first12=Michael |last12=Haas |first13=Daniel |last13=Huber |first14=Jason H. |last14=Steffen |first15=Susan E. |last15=Thompson |first16=Elisa |last16=Quintana |first17=Thomas |last17=Barclay |first18=Martin |last18=Still |first19=Jonathan |last19=Fortney |first20=T. N. |last20=Gautier III |first21=Roger |last21=Hunter |first22=Douglas A. |last22=Caldwell |first23=David R. Ciardi Edna |last23=Devore |first24=William |last24=Cochran |first25=Jon |last25=Jenkins |first26=Eric |last26=Agol |first27=Joshua A. |last27=Carter |first28=John |last28=Geary}}</ref> However, there are some cases where such effects are detected even by planetary-mass companions such as ].<ref>: Daniel Angerhausen, Emily DeLarme, Jon A. Morse</ref> | |||
| ====Through validation==== | |||
| If a planet cannot be detected through at least one of the other other detection methods, it can be confirmed by determining if the possibility of a Kepler candidate being a real planet is significantly larger than any false-positive scenarios combined. One of the first methods was to see if other telescopes can see the transit as well. The first planet confirmed through this method was ] which was also observed with a Spitzer space telescope in addition to analyzing any other false-positive possibilities.<ref name="bbc20111205">{{cite news|url=http://www.bbc.co.uk/news/science-environment-16040655|title=Kepler 22-b: Earth-like planet confirmed|date=December 5, 2011|work=]|accessdate=December 6, 2011}}</ref> Such confirmation is costly, as small planets can generally be detected only with space telescopes. | |||
| In 2014, a new confirmation method called "validation by multiplicity" was announced. From the planets previously confirmed through various methods, it was found that planets in most planetary systems orbit in a relatively flat plane, similar to the planets found in Earth's solar system. This means that if a star has multiple planet candidates, it is very likely a real planetary system.<ref name="NASA-20140226"/> Transit signals still need to meet several criteria which rule out false-positive scenarios. For instance, it has to have considerable signal-to-noise ratio, it has at least three observed transits, orbital stability of those systems have to be stable and transit curve has to have a shape that partly eclipsing binaries could not mimic the transit signal. In addition, its orbital period needs to be 1.6 days or longer to rule out common false positives caused by eclipsing binaries.<ref>: Jack J. Lissauer, Geoffrey W. Marcy, Stephen T. Bryson, Jason F. Rowe, Daniel Jontof-Hutter, Eric Agol, William J. Borucki, Joshua A. Carter, Eric B. Ford, Ronald L. Gilliland, Rea Kolbl, Kimberly M. Star, Jason H. Steffen, Guillermo Torres</ref> Validation by multiplicity method is very efficient and allows to confirm hundreds of Kepler candidates in a relatively short amount of time. | |||
| A similar verification method can be used when follow-up radial velocity observations detect additional planetary candidates even if they fail to detect the targets itself due to their low gravitational influence on their host star. Example of this would be Kepler-93 where a transit signal indicating the presents of a 4.7 day orbital period planet. While radial velocity observations did not detect the 4.7 signature, it detected an unseen companion and orbital configuration turned out to be stable. This allowed to confirm Kepler-93b despite the lack of its detection.<ref>http://astro.berkeley.edu/~gmarcy/22kois.pdf</ref> | |||
| A new validation method using a tool called PASTIS has been developed. It makes it possible to confirm a planet even when only a single candidate transit event for the host star has been detected. A drawback of this tool is that it requires a relatively high signal-to-noise ratio from Kepler data, so it can mainly confirm only larger planets or planets around quiet and relatively bright stars. Currently, the analysis of Kepler candidates through this method is underway.<ref></ref> | |||
| ==Mission results to date== | |||
| ] is towards the lower left corner.]] | |||
| ] ]. ] is towards the lower left corner.]] | |||
| ] is towards the lower left corner.]] | |||
| The ''Kepler'' observatory was in active operation from 2009 through 2013, with the ] announced on January 4, 2010. As expected, the initial discoveries were all short-period planets. As the mission continued, additional longer-period candidates were found. | |||
| ===2009=== | |||
| NASA held a press conference to discuss early science results of the ''Kepler'' mission on August 6, 2009.<ref name="KeplerBriefing20090806">{{cite web| url=http://www.nasa.gov/centers/ames/news/releases/2009/M09-94AR.html |author=NASA Staff |title=NASA Announces Briefing About Kepler's Early Science Results |date=August 3, 2009 |publisher=] |accessdate=April 23, 2011}}</ref> At this press conference, it was revealed that ''Kepler'' had confirmed the existence of the previously known transiting exoplanet ], and was functioning well enough to discover Earth-size planets.<ref name="KeplerPressConf20090806">{{cite web |author=NASA Staff |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-discovery.html |title=NASA's Kepler Spies Changing Phases on a Distant World |date=August 6, 2009 |publisher=] |accessdate=August 6, 2009}}</ref><ref name="kepler_phases"/> | |||
| Since ''Kepler'''s detection of planets depends on seeing very small changes in brightness, stars that vary in brightness all by themselves (]s) are not useful in this search.<ref name="Update20091105"/> From the first few months of data, ''Kepler'' scientists have determined that about 7,500 stars from the initial target list are such variable stars. These were dropped from the target list, and replaced by new candidates. On November 4, 2009, the ''Kepler'' project publicly released the light curves of the dropped stars.<ref>{{cite web |author=NASA Staff |url=http://archive.stsci.edu/mast_news.php?out=html&desc=t&id=342 |title=Kepler dropped stars now public |date=November 4, 2009 |publisher=] |accessdate=April 23, 2011}}</ref> | |||
| The first six weeks of data revealed five previously unknown planets, all very close to their stars.<ref name="sciencenews.org">{{cite web |author=ScienceNews Staff |url=http://www.sciencenews.org/view/generic/id/52465/title/Kepler_space_telescope_finds_its_first_extrasolar_planets |title=Kepler space telescope finds its first extrasolar planets |publisher=] |date=January 30, 2010 |accessdate=February 5, 2011}}</ref><ref>{{cite web |last=MacRobert |first=Robert |title=Kepler's First Exoplanet Results – News Blog |url=http://www.skyandtelescope.com/community/skyblog/newsblog/80621797.html |publisher=] |date=January 4, 2010 |accessdate=April 21, 2011}}</ref> Among the notable results are one of the least dense planets yet found,<ref name="centauri-dreams.org">{{cite web |last=Gilster |first=Paul |url=http://www.centauri-dreams.org/?p=16640 |title=The Remarkable Kepler-11 |publisher=] |date=February 2, 2011 |accessdate=April 21, 2011}}</ref> two low-mass ] stars<ref name="vanKerkwijk2010">{{cite journal |first1=Marten H. |last1=van Kerkwijk |first2=Saul A. |last2=Rappaport |first3=René P. |last3=Breton |first4=Stephen |last4=Justham |first5=Philipp |last5=Podsiadlowski |first6=Zhanwen |last6=Han |title=Observations of Doppler Boosting in Kepler Light Curves |date=May 20, 2010 |journal=] |publisher=IOP Publishing |issn=0004-637X |volume=715|issue=1 |pages=51–58 |bibcode=2010ApJ...715...51V |doi=10.1088/0004-637X/715/1/51|arxiv = 1001.4539 }}</ref> that were initially reported as being members of a new class of stellar objects,<ref name="hotter">{{cite web |last=Villard |first=Ray |title=Blazing Stellar Companion Defies Explanation |url=http://news.discovery.com/space/blazing-stellar-companion-defies-explanation.html |publisher=] |accessdate=April 20, 2011}}</ref> and a ]. | |||
| ===2010=== | |||
| On June 15, 2010, the ''Kepler'' mission released data on all but 400 of the ~156,000 planetary target stars to the public. 706 targets from this first data set have viable exoplanet candidates, with sizes ranging from as small as the Earth to larger than Jupiter. The identity and characteristics of 306 of the 706 targets were given. The released targets included five candidate multi-planet systems. Data for the remaining 400 targets with planetary candidates was to be released in February 2011. (For details about this later data release, see the ''Kepler'' results for ] below.) Nonetheless, the ''Kepler'' results, based on the candidates in the list released in 2010, imply that most candidate planets have radii less than half that of Jupiter. The ''Kepler'' results also imply that small candidate planets with periods less than thirty days are much more common than large candidate planets with periods less than thirty days and that the ground-based discoveries are sampling the large-size tail of the size distribution.<ref name="Borucki2010">{{cite arXiv |last1=Borucki |first1=William J. |coauthors=''et al.'' (Kepler Team) |title=Characteristics of Kepler Planetary Candidates Based on the First Data Set: The Majority are Found to be Neptune-Size and Smaller |eprint=1006.2799 |class=astro-ph.EP |date=2010 }}</ref> This contradicted older theories which had suggested small and Earth-like planets would be relatively infrequent.<ref name="history">{{cite journal |last1=Woolfson |first1=M. M. |title=The Solar System: Its Origin and Evolution |journal=] |volume=34 |pages=1–20 |year=1993 |bibcode=1993QJRAS..34....1W }} Page 18 in particular states that models that required a near collision of stars imply about 1% will have planets.</ref><ref>{{cite journal |title=Protoplanet Migration by Nebula Tides |last1=Ward |first1=W.R. |journal=] |volume=126 |issue=2, |pages=261–281 |year=1997 | |||
| |url=http://www.gps.caltech.edu/classes/ge133/reading/ward_migration.pdf |publisher=] |accessdate=April 23, 2011 |bibcode=1997Icar..126..261W |doi=10.1006/icar.1996.5647 }}</ref> Based on extrapolations from the ''Kepler'' data, an estimate of around 100 million habitable planets in our galaxy may be realistic.<ref>{{cite web |url=http://www.ted.com/talks/dimitar_sasselov_how_we_found_hundreds_of_earth_like_planets.html |last1=Sasselov |first1=Dimitar |title=How we found hundreds of Earth-like planets |publisher=] |date=July 2010 |accessdate=February 5, 2011}}</ref> However, some media reports of the TED talk have led to the misunderstanding that Kepler had actually found these planets. This was clarified in a letter to the Director of the NASA ], for the ''Kepler'' Science Council dated August 2, 2010 states, "Analysis of the current ''Kepler'' data does not support the assertion that ''Kepler'' has found any Earth-like planets."<ref>{{cite web |last1=Dunham |first1=Edward W. |last2=Gautier |first2=Thomas N. |last3=Borucki |first3=William J. |title=NASA Kepler Science Status: Statement to Ames Center Director |url=http://www.spaceref.com/news/viewsr.html?pid=34637 |date=August 3, 2010 |accessdate=April 24, 2011 }}</ref><ref>{{cite journal |last1=Steffen |first1=Jason H. |author2=et al. |title=Five Kepler target stars that show multiple transiting exoplanet candidates |doi=10.1088/0004-637X/725/1/1226 |pages=1226–1241 |volume=725 |journal=] |publisher=IOP Publishing |issn=0004-637X |arxiv=1006.2763 |date=November 9, 2010 |bibcode = 2010ApJ...725.1226S}}</ref><ref name="arXiv-1006.2815v2">{{cite journal |url=http://arxiv.org/pdf/1006.2815v2 |title=Kepler Eclipsing Binary Stars. I. Catalog and Principal Characterization of 1879 Eclipsing Binaries in the First Data Release |date=January 21, 2011 |publisher=] |location=] |format=PDF |arxiv=1006.2815v2 |journal= |first1=Andrej |last1=Prsa |first2=Natalie M. |last2=Batalha |first3=Robert W. |last3=Slawson |first4=Laurance R. |last4=Doyle |first5=William F. |last5=Welsh |first6=Jerome A. |last6=Orosz |first7=Sara |last7=Seager |first8=Michael |last8=Rucker |first9=Kimberly |last9=Mjaseth |first10=Scott G. |last10=Engle |first11=Kyle |last11=Conroy |first12=Jon M. |last12=Jenkins |first13=Douglas A. |last13=Caldwell |first14=David G. |last14=Koch |first15=William J. |last15=Borucki}}</ref> | |||
| In 2010, ''Kepler'' identified two systems containing objects which are smaller and hotter than their parent stars: ] and ].<ref>{{cite journal |first1=Jason F. |last1=Rowe |first2=William J. |last2=Borucki |first3=David |last3=Koch |first4=Steve B. |last4=Howell |first5=Gibor |last5=Basri |first6=Natalie |last6=Batalha |first7=Timothy M. |last7=Brown |first8=Douglas |last8=Caldwell |first9=William D. |last9=Cochran |first10=Edward |last10=Dunham |first11=Andrea K. |last11=Dupree |first12=Jonathan J. |last12=Fortney |first13=Thomas N. |last13=Gautier III |first14=Ronald L. |last14=Gilliland |first15=Jon |last15=Jenkins |first16=David W. |last16=Latham |first17=Jack . J. |last17=Lissauer |first18=Geoff |last18=Marcy |first19=David G. |last19=Monet |first20=Dimitar |last20=Sasselov |first21=William F. |last21=Welsh |title=Kepler Observations of Transiting Hot Compact Objects |year=2010 |journal=] |volume=713 |issue=2 |pages=L150–L154 |bibcode=2010ApJ...713L.150R |doi=10.1088/2041-8205/713/2/L150|arxiv = 1001.3420 }}</ref> These objects are probably low-mass ] stars produced by previous episodes of ] in their systems.<ref name="vanKerkwijk2010"/> | |||
| In 2010, the ''Kepler'' team released a paper which had data for 312 extrasolar planet candidates from 306 separate stars. Only 33.5 days of data were available for most of the candidates.<ref name=Borucki2010/> NASA also announced data for another 400 candidates were being withheld to allow members of the ''Kepler'' team to perform follow-up observations.<ref>{{cite web |author=NASA Staff |title=Kepler News: First 43 Days of Kepler Data Released |url=http://kepler.arc.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=42 |publisher=] |date=May 15, 2010 |accessdate=April 24, 2011 }}</ref> The data for these candidates were made public on February 2, 2011.<ref name=borucki/> | |||
| ===2011=== | |||
| ]<ref name="Kepler20e-20111220" /> and ]<ref name="Kepler20f-20111220" /> with ] and ].]] | |||
| On February 2, 2011, the ''Kepler'' team announced the results of analysis of the data taken between 2 May and September 16, 2009.<ref name="borucki">{{cite arXiv |last1=Borucki |first1=William J. |coauthors=''et al.'' |year=2011 |title=Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data |class=astro-ph.EP |eprint=1102.0541 }}</ref> They found 1235 planetary candidates circling 997 host stars. (The numbers that follow assume the candidates are really planets, though the official papers called them only candidates. Independent analysis indicated that at least 90% of them are real planets and not false positives).<ref>{{cite arXiv |last1=Morton |first1=Timothy D. |last2=Johnson |first2=John Asher |year=2011 |title=On the Low False Positive Probabilities of Kepler Planet Candidates |class=astro-ph.EP |eprint=1101.5630 |author2=John Asher Johnson}}</ref> 68 planets were approximately Earth-size, 288 ]-size, 662 Neptune-size, 165 Jupiter-size, and 19 up to twice the size of Jupiter. In contrast to previous work, roughly 74% of the planets are smaller than Neptune, most likely as a result of previous work finding large planets more easily than smaller ones. | |||
| That February 2, 2011 release of 1235 extrasolar planet candidates, included 54 that may be in the "]", including 5 less than twice the size of the Earth.<ref name="5earths">{{cite web |author=NASA Staff |title=NASA Finds Earth-size Planet Candidates in Habitable Zone, Six Planet System |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=98 |date=February 2, 2011 |publisher=] |accessdate=April 24, 2011 }}</ref><ref name="Overbye">{{cite news |last1=Overbye |first1=Dennis |title=Kepler Planet Hunter Finds 1,200 Possibilities |publisher=New York Times |date=February 2, 2011 |url=http://www.nytimes.com/2011/02/03/science/03planet.html |accessdate=April 24, 2011 }}</ref> There were previously only two planets thought to be in the "habitable zone", so these new findings represent an enormous expansion of the potential number of "]s" (planets of the right temperature to support liquid water).<ref name="Borenstein">{{cite news |last1=Borenstein |first1=Seth |title=NASA spots scores of potentially livable worlds |publisher=] |date=February 2, 2011 |url=http://msnbc.msn.com/id/41387915/ns/technology_and_science-space |accessdate=April 24, 2011 }}</ref> All of the habitable zone candidates found thus far orbit stars significantly smaller and cooler than the Sun (habitable candidates around Sun-like stars will take several additional years to accumulate the three transits required for detection).<ref name="Alexander">{{cite web |last1=Alexander |first1=Amir |title = Kepler Discoveries Suggest a Galaxy Rich in Life |work= |publisher=] |date=February 3, 2011 |url= http://www.planetary.org/news/2011/0203_Kepler_Discoveries_Suggest_a_Galaxy.html |accessdate = February 4, 2011}}</ref> Of all the new planet candidates, 68 are 125% of ]'s size or smaller, or smaller than all previously discovered exoplanets.<ref name="Overbye" /> "Earth-size" and "super-Earth-size" is defined as "less than or equal to 2 Earth radii (Re)" .<ref name=borucki/> Six such planet candidates <ref name=borucki/> are in the "habitable zone."<ref name=5earths /> A more recent study found that one of these candidates (KOI 326.01) is in fact much larger and hotter than first reported.<ref name="Grant">{{cite web |last1=Grant |first1=Andrew |title=Exclusive: "Most Earth-Like" Exoplanet Gets Major Demotion—It Isn't Habitable |url=http://blogs.discovermagazine.com/80beats/2011/03/08/exclusive-most-earth-like-exoplanet-gets-major-demotion%e2%80%94it-isnt-habitable/ |publisher=] |work= |date=March 8, 2011|accessdate=April 24, 2011 }}</ref> | |||
| The frequency of planet observations was highest for exoplanets two to three times Earth-size, and then declined in inverse proportionality to the area of the planet. The best estimate (as of March 2011), after accounting for observational biases, was: 5.4% of stars host Earth-size candidates, 6.8% host super-Earth-size candidates, 19.3% host Neptune-size candidates, and 2.55% host Jupiter-size or larger candidates. Multi-planet systems are common; 17% of the host stars have multi-candidate systems, and 33.9% of all the planets are in multiple planet systems.<ref>{{cite journal |first=William J. |last=Borucki |author2=et al. |year=2011 |title=Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data |arxiv=1102.0541 |bibcode = 2011ApJ...736...19B |doi = 10.1088/0004-637X/736/1/19|journal=The Astrophysical Journal |volume=736 |page=19 |publisher=IOP Publishing |issn=0004-637X}}</ref> | |||
| By December 5, 2011, the ''Kepler'' team announced that they had discovered 2,326 planetary candidates, of which 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Compared to the February 2011 figures, the number of Earth-size and super-Earth-size planets increased by 200% and 140% respectively. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars, marking a decrease from the February figure; this was due to the more stringent criteria in use in the December data.<ref name=KeplerDec2011Results/> | |||
| On December 20, 2011, the ''Kepler'' team announced the discovery of the first ] ], ]<ref name="Kepler20e-20111220" /> and ],<ref name="Kepler20f-20111220" /> orbiting a ], ].<ref name="NASA-20111220" /> | |||
| Based on ''Kepler'''s findings, astronomer ] estimated in 2011 that "within a thousand light-years of Earth", there are "at least 30,000" habitable planets.<ref name="Shostak">{{cite news |last1=Shostak |first1=Seth |title=A Bucketful of Worlds |work=] |date=February 3, 2011 |url=http://www.huffingtonpost.com/seth-shostak/a-bucketful-of-worlds_b_817921.html |accessdate=April 24, 2011 }}</ref> Also based on the findings, the ''Kepler'' team has estimated that there are "at least 50 billion planets in the Milky Way", of which "at least 500 million" are in the ].<ref name="BorensteinS">{{cite news |last1=Borenstein |first1=Seth |title=Cosmic census finds crowd of planets in our galaxy |agency=Associated Press |date=February 19, 2011 |url=http://apnews.excite.com/article/20110219/D9LG45NO0.html |accessdate=April 24, 2011 }}</ref> In March 2011, astronomers at NASA's ] (JPL) reported that about "1.4 to 2.7 percent" of all sunlike stars are expected to have earthlike planets "within the ]s of their stars". This means there are "two billion" of these "Earth analogs" in our own Milky Way galaxy alone. The JPL astronomers also noted that there are "50 billion other galaxies", potentially yielding more than one ] "Earth analog" planets if all galaxies have similar numbers of planets to the Milky Way.<ref name="ChoiCQ">{{cite web |last1=Choi |first1=Charles Q. |url=http://www.space.com/11188-alien-earths-planets-sun-stars.html |title=New Estimate for Alien Earths: 2 Billion in Our Galaxy Alone |date=March 21, 2011 |publisher=] |accessdate=April 24, 2011}}</ref> | |||
| ===2012=== | |||
| In January 2012, an international team of astronomers reported that each star in the ] may host "]", suggesting that over 160 billion star-bound planets may exist in our galaxy alone.<ref name="Space-20120111">{{cite web |last=Wall |first=Mike |title=160 Billion Alien Planets May Exist in Our Milky WayGalaxy |url=http://www.space.com/14200-160-billion-alien-planets-milky-galaxy.html |date=January 11, 2012 |publisher=] |accessdate=January 11, 2012 }}</ref><ref name="Nature-20120111">{{cite journal |author=Cassan, A et al |title=One or more bound planets per Milky Way star from microlensing observations |url=http://www.nature.com/nature/journal/v481/n7380/full/nature10684.html |doi=10.1038/nature10684 |date=January 11, 2012 |journal=] |volume=481 |pages=167–169 |accessdate=January 11, 2012 |bibcode = 2012Natur.481..167C |pmid=22237108 |issue=7380|arxiv = 1202.0903 |last2=Kubas |first2=D. |last3=Beaulieu |first3=J.-P. |last4=Dominik |first4=M. |last5=Horne |first5=K. |last6=Greenhill |first6=J. |last7=Wambsganss |first7=J. |last8=Menzies |first8=J. |last9=Williams |first9=A. |first10=U. G. |first11=A. |first12=D. P. |first13=M. D. |first14=V. |first15=S. |first16=J. A. R. |first17=A. |first18=Ch. |first19=K. H. |first20=S. |first21=D. Dominis |first22=J. |first23=P. |first24=K. |first25=N. |first26=S. |first27=J.-B. |first28=R. |first29=K. R. |first30=K. C. }}</ref> ''Kepler'' also recorded distant ], some of which are 10,000 times more powerful than the superlative 1859 ].<ref name="bbc1">{{cite news |url=http://www.bbc.co.uk/news/science-environment-18089695 |title=Kepler telescope studies star superflares |publisher=BBC News |date=May 17, 2012 |accessdate=May 31, 2012}}</ref> The superflares may be triggered by close-orbiting ]-sized planets.<ref name=bbc1/> The ] (TTV) technique, which was used to discover ], gained popularity for confirming exoplanet discoveries.<ref>. NASA.gov.</ref> A planet in a system with four stars was also confirmed, the first time such a system had been discovered.<ref>.</ref> | |||
| {{As of|2012}}, there were ].<ref name="KeplerDec2011Results">{{cite web |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=165 |title=Kepler-22b, Super-Earth in the habitable zone of a Sun-like Star |work=Kepler |publisher=NASA |date=December 5, 2011}}</ref><ref>{{cite web |url=http://news.sciencemag.org/sciencenow/2011/09/super-earth-found-in-habitable-z.html |title='Super-Earth' Found in Habitable Zone |author=Govert Schilling |date=September 12, 2011 |publisher=AAAS}}</ref><ref>{{cite web|url=http://archive.stsci.edu/kepler/planet_candidates.html|title=Released Kepler Planetary Candidates|publisher=MAST|date=February 27, 2012|accessdate=November 26, 2012}}</ref> Of these, 207 are similar in size to Earth, 680 are super-Earth-size, 1,181 are Neptune-size, 203 are Jupiter-size and 55 are larger than Jupiter. Moreover, 48 planet candidates were found in the habitable zones of surveyed stars. The ''Kepler'' team estimated that 5.4% of all stars host Earth-size planet candidates, and that 17% of all stars have multiple planets. In December 2011, two of the ] candidates, ]<ref name="Kepler20e-20111220">{{cite web |author=] |title=Kepler: A Search For Habitable Planets – Kepler-20e |url=http://kepler.nasa.gov/Mission/discoveries/kepler20e/ |date=December 20, 2011 |publisher=] |accessdate=December 23, 2011 }}</ref> and ],<ref name="Kepler20f-20111220">{{cite web |author=] |title=Kepler: A Search For Habitable Planets – Kepler-20f |url=http://kepler.nasa.gov/Mission/discoveries/kepler20f/ |date=December 20, 2011 |publisher=] |accessdate=December 23, 2011 }}</ref> were confirmed as planets orbiting a ], ].<ref name="NASA-20111220">{{cite web |last=Johnson |first=Michele |title=NASA Discovers First Earth-size Planets Beyond Our Solar System|url=http://www.nasa.gov/mission_pages/kepler/news/kepler-20-system.html|publisher=] |date=December 20, 2011 |accessdate=December 20, 2011}}</ref><ref name="Nature-20111220">{{cite journal |last=Hand |first=Eric |title=Kepler discovers first Earth-sized exoplanets |doi=10.1038/nature.2011.9688 |date=December 20, 2011 |journal=] }}</ref><ref name="NYT-20111220">{{cite news |last=Overbye |first=Dennis |title=Two Earth-Size Planets Are Discovered |url=http://www.nytimes.com/2011/12/21/science/space/nasas-kepler-spacecraft-discovers-2-earth-size-planets.html |date=December 20, 2011 |publisher=] |accessdate=December 21, 2011 }}</ref> | |||
| <!-- ] --> | |||
| ===2013=== | |||
| ] | |||
| According to a study by ] astronomers published in January 2013, the ] contains at least as many planets as it does stars, resulting in 100–400 billion ].<ref name="NASA-20130103">{{cite web |last=Claven|first=Whitney |title=Billions and Billions of Planets |url=http://www.nasa.gov/mission_pages/kepler/news/kepler20130103.html|date=January 3, 2013 |publisher=] |accessdate=January 3, 2013 }}</ref><ref name="Space-20130102">{{cite web |title=100 Billion Alien Planets Fill Our Milky Way Galaxy: Study |url=http://www.space.com/19103-milky-way-100-billion-planets.html |date=January 2, 2013 |publisher=] |accessdate=January 3, 2013 |author=Staff }}</ref> The study, based on planets orbiting the star ''Kepler-32'', suggests that ] may be common around stars in our galaxy. The discovery of 461 more candidates was announced on January 7, 2013.<ref name=kep></ref> The longer Kepler watches, the more planets with long periods it can detect.<ref name=kep/> | |||
| {{Cquote|''Since the last Kepler catalog was released in February 2012, the number of candidates discovered in the Kepler data has increased by 20 percent and now totals 2,740 potential planets orbiting 2,036 stars''. - NASA<ref name=kep/>}} | |||
| A new candidate, announced on January 7, 2013, is ] (formerly, ''KOI-172.02''), an ]-like ] orbiting a ] similar to our ] in the ] and possibly a "prime candidate to host ]".<ref name="Space-20130109">{{cite web |last=Moskowitz |first=Clara |title=Most Earth-Like Alien Planet Possibly Found |url=http://www.space.com/19201-most-earth-like-alien-planet.html |date=January 9, 2013 |publisher=] |accessdate=January 9, 2013 }}</ref> | |||
| In April 2013, a white dwarf star was discovered bending the light of its companion red dwarf star in the KOI-256 star system.<ref> '']'' Accessed April 6, 2013</ref> | |||
| In April 2013, ] announced the discovery of three new ]-like ] – ], ], and ] – in the ]s of their respective host stars, ] and ]. The new exoplanets, which are considered prime candidates for possessing liquid water and thus potentially life, were identified using the ''Kepler'' spacecraft.<ref name="NASA-20130418">{{cite web |last1=Johnson |first1=Michele |last2=Harrington |first2=J.D. |title=NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date |url=http://www.nasa.gov/mission_pages/kepler/news/kepler-62-kepler-69.html |date=April 18, 2013 |publisher=] |accessdate=April 18, 2013 }}</ref><ref name="NYT-20130418">{{cite news |last=Overbye |first=Dennis |title=2 Good Places to Live, 1,200 Light-Years Away |url=http://www.nytimes.com/2013/04/19/science/space/2-new-planets-are-most-earth-like-yet-scientists-say.html |date=April 18, 2013 |work=] |accessdate=18 April 18 }}</ref><ref>{{cite web|url=http://www.youtube.com/watch?v=P8PJt-R5NxI|title=NASA's Kepler Discovers Its Smallest 'Habitable Zone' Planets to Date|publisher=YouTube|date=April 18, 2013|accessdate=April 19, 2013}}</ref> A more recent analysis has shown that Kepler 69c is likely more analogous to Venus, and thus unlikely to be habitable.<ref name="supervenus">{{cite journal |first1=Stephen R. |last1=Kane |first2=Thomas |last2=Barclay |first3=Dawn M. |last3=Gelino |title=A Potential Super-Venus in the Kepler-69 System |publisher=IOP Publishing |issn=2041-8205 |journal=The Astrophysical Journal Letters |arxiv=1305.2933 |year=2013 |bibcode=2013ApJ...770L..20K |volume=770 |page=L20 |doi=10.1088/2041-8205/770/2/L20 |issue=2}}</ref> | |||
| On May 15, 2013, NASA announced the spacecraft had been crippled by failure of a ] that keeps it pointed in the right direction. A second wheel had previously failed, and the spacecraft requires three wheels (out of four total) to be operational for the instrument to function properly. Further testing in July and August determined that while ''Kepler'' was capable of using its damaged reaction wheels to prevent itself from entering safe mode and downlinking previously collected science data it was not capable of collecting further science data as previously configured.<ref>{{cite web |url=http://www.nasa.gov/content/kepler-mission-manager-update-pointing-test-results |title=Kepler Mission Manager Update: Pointing Test Results |date=August 19, 2013 |publisher=] |accessdate=September 9, 2013}}</ref> Scientists working on the Kepler project said there was a ] <!-- NB this purposefully links to the disambiguation page which explains a backlog in general --> of data still to be looked at, and that more discoveries would be made in the following couple of years, despite the setback.<ref>{{cite news| url= http://www.3news.co.nz/Planet-hunting-Kepler-broken-mission-may-be-over/tabid/1160/articleID/298431/Default.aspx| work=3 News NZ| title= Kepler broken - mission may be over| date=May 20, 2013}}</ref> | |||
| Although no new science data from Kepler field had been collected since the problem, an additional sixty-three candidates were announced in July 2013 based on the previously collected observations.<ref name=recovery/> | |||
| In November 2013, the second Kepler science conference was held. The discoveries included the median size of planet candidates getting smaller compared to early 2013, preliminary results of the discovery of a few circumbinary planets and planets in the habitable zone.<ref>http://nexsci.caltech.edu/conferences/KeplerII/agenda.shtml</ref> | |||
| <!-- ] --> | |||
| ===2014=== | |||
| ] of Exoplanet Discoveries - the yellow shaded bar shows newly announced planets including those verified by the multiplicity technique (February 26, 2014).]] | |||
| On February 13, over 530 additional planet candidates were announced residing around single planet systems. Several of them were nearly Earth-sized and located in the habitable zone. This number was further increased by about 400 in June 2014.<ref name="C4Wauto-2478260">{{cite web |url=http://exoplanetarchive.ipac.caltech.edu/ |title=Welcome to the NASA Exoplanet Archive |work=exoplanetarchive.ipac.caltech.edu |date=February 27, 2014 <!-- No date available; last modification date used. --> |quote=February 13, 2014: The Kepler project has updated dispositions for 534 KOIs in the Q1-Q16 KOI activity table. This brings the total number of Kepler candidates and confirmed planets to 3,841. For more information, see the Purpose of KOI Table document and the interactive tables. |accessdate=February 27, 2014 |author=<!--Staff writer(s); no by-line.--> |archiveurl=//web.archive.org/web/20140227025004/http://exoplanetarchive.ipac.caltech.edu/ |archivedate=February 27, 2014 |deadurl=no}}</ref> | |||
| On February 26, scientists announced that data from Kepler had confirmed the existence of 715 new exoplanets. A new statistical method of confirmation was used called “verification by multiplicity” which is based on how many planets around multiple stars were found to be real planets. This allowed much quicker confirmation of numerous candidates which are part of multiplanetary systems. 95% of the discovered exoplanets were smaller than ] and four, including ''Kepler-296f'', were less than 2 1/2 the size of ] and were in ] where surface temperatures are suitable for liquid ].<ref name="NASA-20140226">{{cite web |last1=Johnson |first1=Michele |last2=Harrington |first2=J.D. |title=NASA's Kepler Mission Announces a Planet Bonanza, 715 New Worlds |url=http://www.nasa.gov/ames/kepler/nasas-kepler-mission-announces-a-planet-bonanza/ |date=February 26, 2014 |work=] |accessdate=February 26, 2014 }}</ref><ref name= | |||
| "SP-20140226">{{cite web|last=Wall|first=Mike|title=Population of Known Alien Planets Nearly Doubles as NASA Discovers 715 New Worlds |url=http://www.space.com/24824-alien-planets-population-doubles-nasa-kepler.html |date=February 26, 2014 |work=] |accessdate=February 26, 2014}}</ref><ref name="BBC-20140227">{{cite news |last=Amos |first=Jonathan |title=Kepler telescope bags huge haul of planets |url=http://www.bbc.co.uk/news/science-environment-26362433 |date=February 26, 2014 |work=] |accessdate=February 27, 2014}}</ref><ref name="NYT-20140227">{{cite news |last=Overbye |first=Dennis |title=From Kepler Data, Astronomers Find Galaxy Filled With More but Smaller Worlds |url=http://www.nytimes.com/2014/02/27/science/space/diving-into-kepler-data-astronomers-discover-hundreds-of-planets.html |date=February 27, 2014 |work=] |accessdate=February 28, 2014 }}</ref> | |||
| In March, a study found that small planets with orbital periods of less than 1 day are usually accompanied by at least one additional planet with orbital period of 1–50 days. This study also noted that ultra-short period planets are almost always smaller than 2 Earth radii unless it is a misaligned hot Jupiter.<ref name="arXiv-1403.2379v1">{{cite journal |url=http://arxiv.org/pdf/1403.2379v1 |title=A Study of the Shortest-Period Planets Found With Kepler |date=March 10, 2014 |publisher=] |location=] |accessdate=April 25, 2014 |format=PDF |arxiv=1403.2379v1 |journal= |first1=Roberto |last1=Sanchis-Ojeda |first2=Saul |last2=Rappaport |first3=Joshua N. |last3=Winn |first4=Michael C. |last4=Kotson |first5=Alan M. |last5=Levine |first6=Ileyk El |last6=Mellah}}</ref> | |||
| Kepler data has also helped scientists observe and understand ]e; measurements were collected every half hour so the light curves were especially useful for studying these types of astronomical events.<ref name="super">{{cite journal |url=http://www.nature.com/news/kepler-clue-to-supernova-puzzle-1.14513 |title=Kepler clue to supernova puzzle |work=] |date=January 16, 2014 |publisher=] |issn=1476-4687 |oclc=01586310 |accessdate=February 28, 2014 |doi=10.1038/505274a |pages=274–275 |volume=505 |issue=7483 |first=Ron |last=Cowen |archiveurl=//web.archive.org/web/20140228222851/http://www.nature.com/news/kepler-clue-to-supernova-puzzle-1.14513 |archivedate=February 28, 2014 |deadurl=no}}</ref> | |||
| On April 17, the Kepler team announced the discovery of ], the first nearly Earth-sized planet located in the habitable zone. This planet orbits around a red dwarf.<ref name="NASA-9376058">{{cite web |url=http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star/index.html |title=NASA's Kepler Discovers First Earth-Size Planet In The 'Habitable Zone' of Another Star |work=nasa.gov |date=April 17, 2014 |publisher=] |accessdate=April 26, 2014 |editor=Jessica Culler |others=NASA Official: Brian Dunbar; Image credit(s): 2xNASA Ames/SETI Institute/JPL-Caltech; NASA Ames |first=Jessica |last=Culler |archiveurl=//web.archive.org/web/20140426070848/http://www.nasa.gov/ames/kepler/nasas-kepler-discovers-first-earth-size-planet-in-the-habitable-zone-of-another-star/index.html |archivedate=April 26, 2014 |deadurl=no}}</ref> | |||
| ==Mission status== | |||
| Kepler was launched in 2009 after it was constructed. It was very successful for finding exoplanets, but reaction-wheel failures crippled its extended mission in 2013. | |||
| ===Extension=== | |||
| </ref>]] | |||
| In April 2012, an independent panel of senior NASA scientists recommended that the ''Kepler'' mission be continued through 2016. According to the senior review, ''Kepler'' observations needed to continue until at least 2015 to achieve all the stated scientific goals.<ref>{{cite web |last1=Clark |first1=stephen |url=http://www.spaceflightnow.com/news/n1204/04kepler/ |title=Kepler planet-hunting mission extended until 2016 |date=April 4, 2012 |publisher=Spaceflight anow |accessdate=April 4, 2012}}</ref> On November 14, 2012, NASA announced the completion of Kepler's primary mission, and the beginning of its extended mission, which may last as long as four years.<ref>{{cite web|title=Release : 12–394 – NASA's Kepler Completes Prime Mission, Begins Extended Mission|url=http://www.nasa.gov/home/hqnews/2012/nov/HQ_12-394_Kepler_Completes_Prime_Mission.html|publisher=NASA|accessdate=November 17, 2012}}</ref> | |||
| ===Reaction wheel saga=== | |||
| In July 2012, one of ''Kepler'''s four ]s (wheel 2) failed.<ref name="NASA-20130815" /> On May 11, 2013, a second wheel (wheel 4) failed, threatening the continuation of the mission, as three wheels are necessary for its planet hunting.<ref name=prs/><ref name="nytimes.com"/> ''Kepler'' has not collected science data since May because it is not able to point with sufficient accuracy.<ref name=kep/> On July 18 and 22 reaction wheels 4 and 2 were tested respectively; wheel 4 only rotated counter-clockwise but wheel 2 ran in both directions, albeit with significantly elevated friction levels.<ref>{{cite web|title=Kepler Mission Manager Update: Initial Recovery Tests|url=http://www.nasa.gov/content/kepler-mission-manager-update-initial-recovery-tests/|publisher=]|accessdate=September 9, 2013|date=July 24, 2013}}</ref> A further test of wheel 4 on July 25 managed to achieve bi-directional rotation.<ref name="keprecoverytestNASA">{{cite web |url=http://www.nasa.gov/content/kepler-mission-manager-update-pointing-test |title=Kepler Mission Manager Update: Pointing Test |date=August 2, 2013 |publisher=] |accessdate=August 3, 2013}}</ref> Both wheels, however, exhibited too much friction to be useful.<ref name="SP-20130815" /> On August 2, NASA put out a call for proposals to use the remaining capabilities of ''Kepler'' for other scientific missions. Starting on August 8, a full systems evaluation was conducted. It was determined that wheel 2 could not provide sufficient precision for scientific missions and the spacecraft was returned to a "rest" state to conserve fuel.<ref name="NASA-20130815" /> Wheel 4 was previously ruled out because it exhibited higher friction levels than wheel 2 in previous tests.<ref name=keprecoverytestNASA/> Sending astronauts to fix ''Kepler'' is not an option since it orbits the Sun and is millions of kilometers from Earth.<ref name="SP-20130815" /> | |||
| On August 15, 2013, NASA announced that ''Kepler'' would not continue searching for planets using the transit method after attempts to resolve issues with two of the four reaction wheels failed.<ref name="NASA-20130815" /><ref name="NYT-20130815" /><ref name="SP-20130815" /> An engineering report has been ordered to assess the spacecraft's capabilities, its two good reaction wheels and its thrusters.<ref name="NASA-20130815" /> Concurrently, a scientific study is being conducted to determine whether enough knowledge can be obtained from Kepler's limited scope to justify its $18 million per year cost. Both reports are expected during the fall of 2013, at which time NASA will determine the future of Kepler. | |||
| Possible future uses include searching for asteroids and comets, looking for evidence of supernovas, and finding huge exoplanets through ].<ref name="SP-20130815" /> Another proposal is to modify the software on ''Kepler'' to compensate. Instead of the stars being fixed and stable in ''Kepler'''s field of view, they will drift. However, software could track this drift and more or less completely recover the mission goals despite being unable to hold the stars in a fixed view.<ref>, Aviv Ofir, August 9, 2013</ref> | |||
| Previously collected data continues to be analyzed.<ref name="kep">{{cite web |url=http://www.nasa.gov/mission_pages/kepler/news/keplerm-20130607.html |title=Kepler Mission Manager Update |date=June 7, 2013 |publisher=NASA |accessdate=June 14, 2013}}</ref> It is expected that around 90% of the 3,548 candidate planets previously identified by Kepler will be confirmed when the data analysis is complete, a process that will take several years. As of August 2013, 135 of those candidates have been confirmed.<ref name="SP-20130815" /> | |||
| ===Second Light (K2)=== | |||
| In November 2013, a newly proposed mission plan, initially named ''"K2"'' (also called "Second Light"), was presented for consideration.<ref name="NASA-20131125">{{cite web |last1=Johnson |first1=Michele |editor1-last=Johnson |editor1-first=Michele |title=A Sunny Outlook for NASA Kepler's Second Light |url=http://www.nasa.gov/kepler/a-sunny-outlook-for-nasa-keplers-second-light |date=November 25, 2013 |work=nasa.gov |publisher=] |accessdate=December 12, 2013|archiveurl=//web.archive.org/web/20140418000640/http://www.nasa.gov/kepler/a-sunny-outlook-for-nasa-keplers-second-light/ |archivedate=April 17, 2014 |deadurl=no |others= NASA Official: Brian Dunbar; Image credits: NASA Ames; NASA Ames/W Stenzel}}</ref><ref name="NASA-20131211a">{{cite web |last1=Johnson |first1=Michele |editor1-last=Johnson |editor1-first=Michele |title=Kepler's Second Light: How K2 Will Work |work=nasa.gov |publisher=] |date=December 11, 2013 |url=http://www.nasa.gov/kepler/keplers-second-light-how-k2-will-work/ |accessdate=December 12, 2013 |others=NASA Official: Brian Dunbar; Image credit: NASA Ames/W Stenzel |archiveurl=//web.archive.org/web/20140418001138/http://www.nasa.gov/kepler/keplers-second-light-how-k2-will-work/ |archivedate=April 17, 2014 |deadurl=no}}</ref><ref name="NASA-20131211b">{{cite web |first=Roger |last=Hunter |editor1-last=Johnson |editor1-first=Michele |title=Kepler Mission Manager Update: Invited to 2014 Senior Review |work=nasa.gov |publisher=] |date=December 11, 2013 |url=http://www.nasa.gov/kepler/kepler-mission-manager-update-invited-to-2014-senior-review |accessdate=December 12, 2013 |others=NASA Official: Brian Dunbar; |archiveurl=//web.archive.org/web/20140418001405/http://www.nasa.gov/kepler/kepler-mission-manager-update-invited-to-2014-senior-review/ |archivedate=April 17, 2014 |deadurl=no}}</ref><ref name=wall>{{cite web |last=Wall |first=Mike |title=NASA's Hobbled Planet-Hunting Spacecraft May Resume Search for Alien Worlds |work=Space.com|publisher=] |date=November 5, 2013 |url=http://www.space.com/23465-planet-hunting-kepler-spacecraft-future.html |accessdate=April 17, 2014 |others= Image credit: NASA |archiveurl=//web.archive.org/web/20140418002147/http://www.space.com/23465-planet-hunting-kepler-spacecraft-future.html |archivedate=April 17, 2014 |deadurl=no}}</ref> ''K2'' would involve using Kepler's remaining capability, ] of about 300 parts per million, compared with about 20 parts per million earlier, to collect data for the study of "], ] and ] such as ] and ], ... " and for finding and studying more ].<ref name="NASA-20131125" /><ref name="NASA-20131211a" /><ref name=wall/> In this proposed mission plan, Kepler would search a much larger area in the plane of ] around the ].<ref name="NASA-20131125" /><ref name="NASA-20131211a" /><ref name=wall/> | |||
| {{wide image|NASA-KeplerSecondLight-K2-Explained-20131211.jpg|600px|Kepler's "Second Light" (''K2'') Proposal Explained (December 11, 2013).<ref name="NASA-20131211a" />}} | |||
| In early 2014, the spacecraft underwent successful testing for the ''K2'' mission.<ref name="C4WDefault-NASAkepler2014-02-14">{{cite web |url=http://www.nasa.gov/ames/kepler/kepler-mission-manager-update-k2-spacecraft-operation-tests-continue/ |title=Kepler Mission Manager Update: K2 spacecraft operation tests continue |work=nasa.gov |publisher=] |date=February 14, 2014 |accessdate=April 17, 2014 |first=Roger |last=Hunter |editor1-last=Johnson |editor1-first=Michele |others=NASA Official: Brian Dunbar; Image Credit: NASA Ames/T. Barclay|archiveurl=//web.archive.org/web/20140418002638/http://www.nasa.gov/ames/kepler/kepler-mission-manager-update-k2-spacecraft-operation-tests-continue/ |archivedate=April 17, 2014 |deadurl=no}}</ref> From March to May 2014, data from a new field called Field 0 was collected as a testing run.<ref name="arXiv-1404.4417v1">{{cite journal |url=http://arxiv.org/pdf/1404.4417v1 |title=HAT-P-54b: A Hot Jupiter Transiting a 0.64 Msun Star in Field 0 of the K2 Mission |date=April 17, 2014 |publisher=] |location=] |accessdate=June 12, 2014 |format=PDF |arxiv=1404.4417v1 |journal= |first1=G. Á. |last1=Bakos |first2=J. D. |last2=Hartman |first3=W. |last3=Bhatti |first4=A. |last4=Bieryla |first5=M. |last5=de Val-Borro |first6=D. W. |last6=Latham |first7=L. A. |last7=Buchhave |first8=Z. |last8=Csubry |first9=K. |last9=Penev |first10=G. |last10=Kovács |first11=B. |last11=Béky |first12=E. |last12=Falco |first13=T. |last13=Kovács |first14=A. W. |last14=Howard |first15=J. A. |last15=Johnson |first16=H. |last16=Isaacson |first17=G. W. |last17=Marcy |first18=G. |last18=Torres |first19=R. W. |last19=Noyes |first20=P. |last20=Berlind |first21=M. L. |last21=Calkins |first22=G. A. |last22=Esquerdo |first23=J. |last23=Lázár |first24=I. |last24=Papp |first25=P. |last25=Sári}}</ref> On May 16, 2014, NASA announced the approval of extending the Kepler mission to the ''K2'' mission.<ref name="NASA-20140516" /> Kepler's photometric precision for the K2 mission is estimated to be 50 ppm on a magnitude 12 star for a 6.5 hour integration.<ref name="C4WDefault-2446741">{{cite web |url=http://keplerscience.arc.nasa.gov/K2/ |title=Kepler Guest Observer Program |work=keplerscience.arc.nasa.gov |date=May 29, 2014 <!-- last modification date used. --> |accessdate=June 12, 2014 |author1=<!--Staff writer(s); no by-line.--> |editor1-first=Martin |editor1-last=Still |others=NASA Official: Jessie Dotson |archiveurl=//web.archive.org/web/20140613045308/http://keplerscience.arc.nasa.gov/K2/ |archivedate=June 12, 2014 |deadurl=no}}</ref> In February 2014, photometric precision for the K2 mission using two-wheel, fine-point precision operations was measured as 44 ppm on magnitude 12 stars for a 6.5 hour integration. The analysis of these measurements posted by NASA stated that the measurements "suggest" the K2 photometric precision "approaches" that of the Kepler archive of three-wheel, fine-point precision data.<ref name="C4WDefault-9014554">{{cite web |url=http://keplerscience.arc.nasa.gov/K2/Performance.shtml |title=K2 Performance |work=keplerscience.arc.nasa.gov |date=May 29, 2014 |accessdate=June 12, 2014 |author1=<!--Staff writer(s); no by-line.--> |editor1-first=Martin |editor1-last=Still |others=NASA Official: Jessie Dotson |archiveurl=//web.archive.org/web/20140613045540/http://keplerscience.arc.nasa.gov/K2/Performance.shtml |archivedate=June 12, 2014 |deadurl=no}}</ref> | |||
| Field 1 of the K2 mission is set towards the ]-] region of the sky and Field 2 is towards the "head" area of ] and includes two globular clusters: ] and ]<ref name="arXiv-1405.7690v1">{{cite journal |url=http://arxiv.org/pdf/1405.7690v1 |title=Cepheids and RR Lyrae Stars in the K2 Fields |date=May 29, 2014 |publisher=] |location=] |accessdate=May 31, 2014 |format=PDF |arxiv=1405.7690v1 |journal= |first1=L. |last1=Molnár |first2=E. |last2=Plachy |first3=R. |last3=Szabó}}</ref> and part of the ] which is only about 11 million years old<ref name="Pecaut">{{Cite journal|author=Mark J. Pecaut, Eric E. Mamajek, & Eric J. Bubar|date=February 2012|title=A Revised Age for Upper Scorpius and the Star Formation History among the F-type Members of the Scorpius-Centaurus OB Association|journal=Astrophysical Journal|volume=746|issue=2|pages=154|url=http://adsabs.harvard.edu/abs/2012ApJ...746..154P|arxiv = 1112.1695 |bibcode = 2012ApJ...746..154P |doi = 10.1088/0004-637X/746/2/154 }}</ref> and at a distance of 380-470 light years<ref>{{cite journal|title=A Hipparcos Census of Nearby OB Associations|author=de Zeeuw, P.T., Hoogerwerf, R., de Bruijne, J.H.J., Brown, A.G.A., & Blaauw, A.|year=1999|journal=Astronomical Journal|volume=117|issue=1|pages=354–399|bibcode=1999AJ....117..354D|doi=10.1086/300682|arxiv = astro-ph/9809227 |url=http://iopscience.iop.org/1538-3881/117/1/354/fulltext/ }}</ref> with probably over 1000 members.<ref>{{cite journal|bibcode=2002AJ....124.1670M|author=Mamajek, E.E., Meyer, M.R., & Liebert, J.|year=2002|journal=Astronomical Journal|volume=124|issue=3|pages=1670–1694|title=Post-T Tauri Stars in the Nearest OB Association|doi=10.1086/341952|arxiv = astro-ph/0205417 }}</ref> | |||
| ==Data releases== | |||
| The ''Kepler'' team originally promised to release data within one year of observations.<ref>{{cite web |url=http://kepler.nasa.gov/Mission/QuickGuide/faq/#a9 |title=Frequently Asked Questions from the Public |accessdate=September 6, 2011}} This ''Kepler'' FAQ states: "Data for each 3-month observation period will be made public within one year of the end the observation period".</ref> However, this plan was changed after launch, with data being scheduled for release up to three years after its collection.<ref name="release">{{cite web|title=NASA's Kepler Mission Data Release Schedule|url=http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml|publisher=]|accessdate=October 18, 2011}} On this schedule, the data from the quarter ending June 2010 was scheduled to be released in June 2013.</ref> This resulted in considerable criticism,<ref>{{cite news |title=In the Hunt for Planets, Who Owns the Data? |author=Dennis Overbye |url=http://www.nytimes.com/2010/06/15/science/space/15kepler.html |publisher=New York Times |date=June 14, 2010}}</ref><ref>{{cite web |url=http://www.nature.com/news/2010/100414/full/news.2010.182.html |title=Telescope team may be allowed to sit on exoplanet data |author=Eric Hand |publisher=Nature |date=April 14, 2010 }}</ref><ref>{{cite web |url=http://www.skyandtelescope.com/news/home/122602884.html |title=Kepler's Exoplanets: A Progress Report |author= Alan MacRobert |date=August 2011 |publisher=S ky and Telescope}}</ref><ref>{{cite web |title=Minutes of the Kepler Users Panel |url=http://keplergo.arc.nasa.gov/docs/KUP_minutes_Mar2011.pdf |date=March 28–29, 2011 |author=Alex Brown}}</ref><ref>{{cite web |url=http://news.discovery.com/space/kepler-exoplanet-controversy-erupts.html |title=KEPLER EXOPLANET CONTROVERSY ERUPTS |author=Nicole Gugliucci |date=June 15, 2010 |publisher=Discovery news}}</ref> leading the ''Kepler'' science team to release the third quarter of their data one year and nine months after collection.<ref>{{cite web |url=http://kepler.nasa.gov/news/nasakeplernews/index.cfm?FuseAction=ShowNews&NewsID=145 |title=NASA's Kepler Mission Announces Next Data Release to Public Archive}}</ref> The data through September 2010 (quarters 4, 5, and 6) was made public in January 2012.<ref>{{cite web |url=http://keplergo.arc.nasa.gov/ArchiveSchedule.shtml|title= Kepler Data Collection and Archive Timeline|accessdate=January 1, 2012}}</ref> | |||
| ===Follow-ups by others=== | |||
| Periodically, the ''Kepler'' team releases a list of candidates (], or KOIs) to the public. Using this information, a team of astronomers collected ] data using the ] to confirm the existence of the candidate KOI-428b in 2010, later named ].<ref name="exoplanet1">{{cite web |first1=A. |last1=Santerne |first2=R. F. |last2=Diaz |first3=F. |last3=Bouchy |first4=M. |last4=Deleuil |first5=C. |last5=Moutou |first6=G. |last6=Hebrard |first7=A. |last7=Eggenberger |first8=D. |last8=Ehrenreich |first9=C. |last9=Gry |first10=S. |last10=Udry |url=http://exoplanet.eu/papers/koi428-vf.3.pdf |title=SOPHIE velocimetry of Kepler transit candidates II. KOI-428b: a hot Jupiter transiting a subgiant F-star |date=November 30, 2010 |accessdate=April 23, 2011 |publisher=EDP Sciences |issn=0004-6361 |doi=10.1051/0004-6361/201015764 |volume=528 |page=A63 |journal=Astronomy & Astrophysics |arxiv=1101.0196v1 }}</ref> In 2011, the same team confirmed candidate KOI-423b, later named ].<ref name="exoplanet2">{{cite arXiv |last1=Bouchy|first1=F. |coauthors=''et al.'' |year=2011 |title= SOPHIE velocimetry of Kepler transit candidates III. KOI-423b: An 18 Mjup transiting companion around an F7IV star|class= astro-ph.EP|eprint=1106.3225}}</ref> | |||
| ===Citizen scientist participation=== | |||
| Since December 2010, ''Kepler'' mission data has been used for the ] project "Planethunters.org", which allows volunteers to look for transit events in the light curves of ''Kepler'' images to identify planets that computer ]s might miss.<ref>{{cite web |last1=Andrews |first1=Bill |title=Become a Planet Hunter! |url=http://cs.astronomy.com/asycs/blogs/astronomy/archive/2010/12/20/become-a-planet-hunter.aspx |publisher=] |date=December 20, 2010 |accessdate=April 24, 2011 }}</ref> By June 2011, users had found sixty-nine potential candidates that were previously unrecognized by the ''Kepler'' mission team.<ref>{{cite web |author=Zooniverse Staff |title=Planetometer |url=http://www.planethunters.org/planetometer |publisher=] |accessdate=June 15, 2011 }}</ref> The team has plans to publicly credit amateurs who spot such planets. | |||
| In January 2012, the ] (BBC) program '']'' aired a public appeal for volunteers to analyse Planethunters.org data for potential new exoplanets. This led two amateur astronomers—one in ], ]—to discover a new ]-sized exoplanet, to be named Threapleton Holmes B.<ref>{{cite news|last= |first= |url=http://www.telegraph.co.uk/science/space/9026837/Amateur-stargazers-discover-new-planet.html |work=] |title=Amateur stargazers discover new planet |publisher=] |date=January 20, 2012 |accessdate=January 20, 2012}}</ref> One hundred thousand other volunteers are also engaged in the search by late January, analyzing over one million ''Kepler'' images by early 2012.<ref>{{cite news |url=http://www.bbc.co.uk/news/science-environment-16612181 |title=Stargazing viewer in planet coup |publisher=BBC News |date=January 18, 2012 |accessdate=January 19, 2012}}</ref> | |||
| ==Confirmed exoplanets== | |||
| {{Update|section|date=June 2014}} | |||
| <!--] next to Jupiter and Earth for scale]]--> | |||
| ] | |||
| {{main|List of exoplanets discovered using the Kepler spacecraft}} | |||
| {{see also|List of exoplanetary host stars|List of multiplanetary systems}} | |||
| In addition to discovering hundreds of exoplanet candidates, the ''Kepler'' spacecraft has also reported twenty-six exoplanets in eleven systems that have not yet been added to the Extrasolar Planet Database.<ref name="11-new-solar-systems">{{cite news|last=O'Neill|first=Ian|title=11 New Alien Solar Systems Crammed with Exoplanets|url=http://news.discovery.com/space/11-new-alien-solar-systems-crammed-with-exoplanets-120126.html|accessdate=January 26, 2012|newspaper=Discovery News|date=January 26, 2012}}</ref> Exoplanets discovered using ''Kepler''<nowiki>'</nowiki>s data, but confirmed by outside researchers, include ],<ref name="exoplanet2"/> ],<ref name="exoplanet1"/> ],<ref name="KOI-196b">{{cite web|author=cyril DEDIEU |url=http://exoplanet.eu/star.php?st=KOI-196 |title=Star: KOI-196 |publisher=Extrasolar Planets Encyclopaedia |accessdate=December 21, 2011}}</ref> ],<ref name="KOI-135b">{{cite web|author=|url=http://exoplanet.eu/star.php?st=KOI-135 |title=Star: KOI-135 |publisher=Extrasolar Planets Encyclopaedia |accessdate= 2011}}</ref> ],<ref name="KOI-204b">{{cite web|author=|url=http://exoplanet.eu/star.php?st=KOI-204 |title=Star: KOI-204 |publisher=Extrasolar Planets Encyclopaedia |accessdate= 2011}}</ref> ],<ref name="KOI-254b">{{cite web|author=|url=http://exoplanet.eu/star.php?st=KOI-254 |title=Star: KOI-254 |publisher=Extrasolar Planets Encyclopaedia |accessdate= 2011}}</ref> ],<ref name="KOI-730">{{cite web|author=|url=http://exoplanet.eu/star.php?st=KOI-730 |title=Star: KOI-730 |publisher=Extrasolar Planets Encyclopaedia |accessdate= 2011}}</ref> and ].<ref name="KOI-961">{{cite web|author=|url=http://exoplanet.eu/star.php?st=KOI-961 |title=Star: KOI-961 |publisher=Extrasolar Planets Encyclopaedia |accessdate= 2012}}</ref> The "KOI" acronym indicates that the star is a ''K''epler ''O''bject of ''I''nterest. | |||
| Both Corot<ref>{{cite journal | |||
| |title=The changing phases of extrasolar planet CoRoT-1b | |||
| |last1=Snellen |first1=I.A.G. | |||
| |last2=De Mooij |first2=E.J.W. | |||
| |last3=Albrecht |first3=S. | |||
| |journal=Nature | |||
| |volume=459 | |||
| |issue=7246 | |||
| |pages=543–545 | |||
| |year=2009 | |||
| |doi=10.1038/nature08045 | |||
| |bibcode = 2009Natur.459..543S | |||
| |pmid=19478779 | |||
| |arxiv = 0904.1208}} </ref> and ''Kepler''<ref name="kepler_phases">{{cite journal |url=http://www.sciencemag.org/content/325/5941/709.full |title=Kepler’s Optical Phase Curve of the Exoplanet HAT-P-7b |work=] |date=August 7, 2009 |publisher=] |location=] |issn=1095-9203 |oclc=1644869 |accessdate=March 23, 2014 |registration=yes |volume=325 |issue=5941 |page=709 |doi=10.1126/science.1178312 |pmid=19661420 |bibcode = 2009Sci...325..709B|first1=W. J. |last1=Borucki |first2=D. |last2=Koch |first3=J. |last3=Jenkins |first4=D. |last4=Sasselov |first5=R. |last5=Gilliland |first6=N. |last6=Batalha |first7=D. W. |last7=Latham |first8=D. |last8=Caldwell |first9=G. |last9=Basri |first10=T. |last10=Brown |first11=J. |last11=Christensen-Dalsgaard |first12=W. D. |last12=Cochran |first13=E. |last13=Devore |first14=E. |last14=Dunham |first15=A. K. |last15=Dupree |first16=T. |last16=Gautier |first17=J. |last17=Geary |first18=A. |last18=Gould |first19=S. |last19=Howell |first20=H. |last20=Kjeldsen |first21=J. |last21=Lissauer |first22=G. |last22=Marcy |first23=S. |last23=Meibom |first24=D. |last24=Morrison |first25=J. |last25=Tarter}}</ref> measured the reflected light from planets. However, these planets were already known, because they transit their star. ''Kepler'''s data allowed the first discovery of planets by this method, ] and ].<ref name="Nature-7097168">{{cite journal |url=http://www.nature.com/nature/journal/v480/n7378/full/nature10631.html |title=A compact system of small planets around a former red-giant star |work=] |date=December 22, 2011 |publisher=] |issn=1476-4687 |oclc=01586310 |accessdate=March 23, 2014 |doi=10.1038/nature10631 |pages=496–499 |volume=480 |issue=7378 |subscription=no |first1=S. |last1=Charpinet |first2=G. |last2=Fontaine |first3=P. |last3=Brassard |first4=E. M. |last4=Green |first5=V. |last5=vanGrootel |first6=S. K. |last6=Randall |first7=R. |last7=Silvotti |first8=A. S. |last8=Baran |first9=R. H. |last9=øStensen |first10=S. D. |last10=Kawaler |first11=J. H. |last11=Telting |archiveurl=//web.archive.org/web/20140323230558/http://www.nature.com/nature/journal/v480/n7378/full/nature10631.html |archivedate=March 23, 2014 |deadurl=no}}</ref> | |||
| ==''Kepler'' Input Catalog== | |||
| {{Main|Kepler Input Catalog}} | |||
| The '''Kepler Input Catalog''' (or '''KIC''') is a publicly searchable database of roughly 13.2 million targets used for the and ''Kepler'' Mission.<ref name="kic">{{cite web |author=NASA Staff |url=http://archive.stsci.edu/kepler/kic10/help/search_help.html |title=MAST KIC Search Help |publisher=] |accessdate=April 23, 2011}}</ref><ref>{{cite web |author=NASA Staff |url=http://archive.stsci.edu/kepler/kic10/search.php |title=KIC10 Search |accessdate=April 23, 2011}}</ref> The catalog alone is not used for finding ''Kepler'' targets, because only a portion of the listed stars (about one-third of the catalog) can be observed by the spacecraft.<ref name=kic/> | |||
| ==See also== | |||
| {{Portal|Astrobiology}} | |||
| *], the first exoplanet confirmed by ''Kepler'' to have an average orbital distance within its star's ] | |||
| *] | |||
| ;Related or comparable missions and projects | |||
| {{colbegin|2}} | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
| *] | |||
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| *] | |||
| *] | |||
| *] | |||
| {{colend}} | |||
| ==Notes== | |||
| {{notelist-ua}} | |||
| ==References== | |||
| {{Reflist|colwidth=30em}} | |||
| ==Further reading== | |||
| *{{cite web | title= Star : Kepler-10 | work=EPE | publisher=Extrasolar Planets Encyclopaedia | url=http://exoplanet.eu/star.php?st=Kepler-10 | accessdate=January 11, 2011 }} | |||
| ==External links== | |||
| {{Commons category|Kepler Mission}} | |||
| * – ]. | |||
| * . | |||
| * . | |||
| * . | |||
| * – ]. | |||
| * . | |||
| * – ]. | |||
| * . | |||
| * . | |||
| * . | |||
| * . | |||
| * {{Twitter|NASAKepler}}. | |||
| ;] catalogs and databases | |||
| * (]) | |||
| * (PHL/]) | |||
| * (] PlanetQuest) | |||
| {{Discovery}} | |||
| {{Space observatories}} | |||
| {{Exoplanet search projects}} | |||
| {{NASA navbox}} | |||
| {{Orbital launches in 2009}} | |||
| {{DEFAULTSORT:Kepler (Spacecraft)}} | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| ] | |||
| {{Link GA|id}} | |||
Revision as of 21:04, 24 June 2014
feck her right in the