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{{short description|Planet smaller than Earth}} |
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'''Sub-Earth''' is a classification of ]s "substantially less massive" than ] and ].<ref name="STEP" /> In the ], this category includes ] and ]. Sub-Earth exoplanets are the most difficult planet type to detect because their small sizes and masses produce the weakest signal. Despite the difficulty, one of the first ]s found was a sub-Earth around a ] ]. ] opened the realm of sub-Earths by discovering them. On January 10, 2012 Kepler discovered the first three sub-Earths around an ordinary star ]. As of June 2014, Kepler has 45 confirmed planets that are smaller than Earth with 17 of them being smaller than 0.8 R<sub>ⴲ</sub>. In addition, there are over 310 planet candidates with the estimated radius of <1R<sub>ⴲ</sub> with 135 of them being smaller than 0.8 R<sub>ⴲ</sub>.<ref name="STEP">{{cite arxiv |eprint=1308.6308 |title=Below One Earth Mass: The Detection, Formation, and Properties of Subterrestrial Worlds |date=2013-08-28 |work=] |first2=B. |first3=L. |first4=E. |class=astro-ph.EP |last1=Sinukoff |first1=E. |last2=Fulton |last3=Scuderi |last4=Gaidos}}</ref> <ref>http://exoplanetarchive.ipac.caltech.edu/</ref> |
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], ], and exoplanets of ] and ].]] |
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A '''sub-Earth''' is a ] "substantially less massive" than ] and ].<ref name="STEP" /> In the ], this category includes ] and ]. Sub-Earth ]s are among the most difficult type to detect because their small sizes and masses produce the weakest signal. Despite the difficulty, one of the first ]s found was a sub-Earth around a ] ]. The smallest known is ] with a size of 0.15 Earth radii, or somewhat smaller than ]. However, ] is not massive enough to qualify as a sub-Earth ] and is instead defined as a ], or ], planet.<ref name="discovery">{{Cite journal|arxiv=1510.06387|last1=Vanderburg|first1=Andrew|title=A disintegrating minor planet transiting a white dwarf|journal=Nature|volume=526|issue=7574|pages=546–549|author2=John Asher Johnson|last3=Rappaport|first3=Saul|last4=Bieryla|first4=Allyson|last5=Irwin|first5=Jonathan|author6=John Arban Lewis|last7=Kipping|first7=David|last8= Brown|first8=Warren R.|last9=Dufour|first9=Patrick|last10= Ciardi|first10=David R.|last11=Angus|first11=Ruth|last12=Schaefer|first12=Laura|author12-link=Laura K. Schaefer|last13= Latham|first13=David W.|last14=Charbonneau|first14=David|last15=Beichman|first15=Charles|last16=Eastman|first16=Jason|last17=McCrady|first17=Nate|last18= Wittenmyer|first18=Robert A.|last19= Wright|first19=Jason T.|display-authors=4|year=2015|doi=10.1038/nature15527|pmid=26490620|bibcode = 2015Natur.526..546V |s2cid=4451207 }}</ref> It is orbiting within a thick cloud of dust and gas as chunks of itself continually break off to then spiral in towards the star, and within around 5,000 years it will have more-or-less disintegrated.<ref>{{cite journal |title=Drifting asteroid fragments around WD 1145+017 |first1=S. |last1=Rappaport |first2=B. L. |last2=Gary |first3=T. |last3=Kaye |first4=A. |last4=Vanderburg |first5=B. |last5=Croll |first6=P. |last6=Benni |first7=J. |last7=Foote |journal=Monthly Notices of the Royal Astronomical Society |volume=458 |issue=4 |date=June 2016 |pages=3904–3917 |doi=10.1093/mnras/stw612 |doi-access=free |arxiv=1602.00740 |bibcode=2016MNRAS.458.3904R }}</ref> |
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Sub-Earths commonly lack substantial atmospheres because of their low gravity and weak ]s, allowing stellar radiation to wear away the atmospheres.<ref name="STEP" /> Due to their small sizes, and unless there's significant ]s when orbiting close to the parent star, sub-Earths also have short periods of geologic activity. |
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The ] space telescope opened up a new realm of sub-Earth discoveries. On January 10, 2012, Kepler discovered the first three sub-Earths around an ordinary star, ]. As of June 2014, Kepler has 45 confirmed planets that are smaller than Earth, with 17 of them being smaller than 0.8 R<sub>ⴲ</sub>. In addition, there are over 310 planet candidates with an estimated radius of <1 R<sub>ⴲ</sub>, with 135 of them being smaller than 0.8 R<sub>ⴲ</sub>.<ref name="STEP">{{cite journal |arxiv=1308.6308 |title=Below One Earth Mass: The Detection, Formation, and Properties of Subterrestrial Worlds |date=2013-08-28 |first2=B. |first3=L. |first4=E. |last1=Sinukoff |first1=E. |last2=Fulton |last3=Scuderi |last4=Gaidos |doi=10.1007/s11214-013-0019-1 |volume=180 |journal=Space Science Reviews |issue=1–4 |pages=71–99|bibcode=2013SSRv..180...71S |s2cid=255071638 }}</ref><ref></ref> |
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There is suspected to be a sub-Earth orbiting ], the closest star to the Sun.<ref></ref> The mass of ] is believed to be between that of Mars and Venus.<ref name="FariaSuárezMascareño2022">{{cite journal|last1=Faria|first1=J. P.|last2=Suárez Mascareño|first2=A.|last3=Figueira|first3=P.|last4=Silva|first4=A.M.|last5=Damasso|first5=M.|last6=Demangeon|first6=O.|last7=Pepe|first7=F.|last8=Santos|first8=N.C.|last9=Rebolo|first9=R.|last10=Cristiani|first10=S.|last11=Adibekyan|first11=V.|last12=Alibert|first12=Y.|last13=Allart|first13=R.|last14=Barros|first14=S.C.C.|last15=Cabral|first15=A.|last16=D’Odorico|first16=V.|last17=Di Marcantonio|first17=P.|last18=Dumusque|first18=X.|last19=Ehrenreich|first19=D.|last20=González Hernández|first20=J. I.|last21=Hara|first21=N.|last22=Lillo-Box|first22=J.|last23=Lo Curto|first23=G.|last24=Lovis|first24=C.|last25=Martins|first25=C.J.A.P.|last26=Mégevand|first26=D.|last27=Mehner|first27=A.|last28=Micela|first28=G.|last29=Molaro|first29=P.|last30=Nunes|first30=N. J.|last31=Pallé|first31=E.|last32=Poretti|first32=E.|last33=Sousa|first33=S. G.|last34=Sozzetti|first34=A.|last35=Tabernero|first35=H.|last36=Udry|first36=S.|last37=Zapatero Osorio|first37=M. R.|display-authors=4|title=A candidate short-period sub-Earth orbiting Proxima Centauri|journal=Astronomy and Astrophysics|date=February 2022|volume=658|page=A115|arxiv=2202.05188|doi=10.1051/0004-6361/202142337|doi-access=free|bibcode=2022A&A...658A.115F }}</ref> |
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Sub-Earths commonly lack substantial atmospheres because of their low gravity and weak ]s, allowing stellar radiation to wear away their atmospheres.<ref name="STEP" /> Due to their small sizes, and unless there are significant ]s when orbiting close to the parent star, sub-Earths also have short periods of geologic activity. |
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== References == |
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== References == |
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Sub-Earths commonly lack substantial atmospheres because of their low gravity and weak magnetic fields, allowing stellar radiation to wear away their atmospheres. Due to their small sizes, and unless there are significant tidal forces when orbiting close to the parent star, sub-Earths also have short periods of geologic activity.
