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| A '''mini-Neptune''' (sometimes known as a ] or '''transitional planet''') is a planet of up to 10 ]es ({{Earth mass}}), less massive than ] and ], which have about 14.5 {{Earth mass}} and 17 {{earth mass}}, respectively. Mini-Neptunes have thick ]–] atmospheres, probably with deep layers of ice, rock or liquid oceans (made of ], ], a mixture of both, or heavier volatiles). These planets have small cores made of low-density volatiles.{{Citation needed|date=January 2016}} | A '''mini-Neptune''' or sub-Neptune (sometimes known as a ] or '''transitional planet''') is a planet of up to 10 ]es ({{Earth mass}}), less massive than ] and ], which have about 14.5 {{Earth mass}} and 17 {{earth mass}}, respectively. Mini-Neptunes have thick ]–] atmospheres, probably with deep layers of ice, rock or liquid oceans (made of ], ], a mixture of both, or heavier volatiles). These planets have small cores made of low-density volatiles.{{Citation needed|date=January 2016}} | ||
| Theoretical studies of such planets are loosely based on knowledge about Uranus and Neptune. Without a thick atmosphere, it would be classified as an ] instead.<ref>, E.J.W. de Mooij (1), M. Brogi (1), R.J. de Kok (2), J. Koppenhoefer (3,4), S.V. Nefs (1), I.A.G. Snellen (1), J. Greiner (4), J. Hanse (1), R.C. Heinsbroek (1), C.H. Lee (3), P.P. van der Werf (1),</ref> An estimated dividing line between a rocky planet and a gaseous planet is around |
Theoretical studies of such planets are loosely based on knowledge about Uranus and Neptune. Without a thick atmosphere, it would be classified as an ] instead.<ref>, E.J.W. de Mooij (1), M. Brogi (1), R.J. de Kok (2), J. Koppenhoefer (3,4), S.V. Nefs (1), I.A.G. Snellen (1), J. Greiner (4), J. Hanse (1), R.C. Heinsbroek (1), C.H. Lee (3), P.P. van der Werf (1),</ref> An estimated dividing line between a rocky planet and a gaseous planet is around 1.6-2.0 Earth radii.<ref>, Daniel C. Fabrycky, Jack J. Lissauer, Darin Ragozzine, Jason F. Rowe, Eric Agol, Thomas Barclay, Natalie Batalha, William Borucki, David R. Ciardi, Eric B. Ford, John C. Geary, Matthew J. Holman, Jon M. Jenkins, Jie Li, Robert C. Morehead, Avi Shporer, Jeffrey C. Smith, Jason H. Steffen, Martin Still</ref><ref>, blogs.scientificamerican.com, 20 June 2012</ref> Planets with larger radii and measured masses are mostly low-density and require an extended atmosphere to simultaneously explain their masses and radii, and empirical observations are showing that planets larger than approximately 1.6 Earth-radius (more massive than approximately 6 Earth-masses) contain significant amounts of volatiles or H–He gas (such planets appear to have a diversity of compositions that is not well-explained by a single mass–radius relation as that found in rocky planets).<ref>Benjamin J. Fulton et al. "</ref><ref>Courtney D. Dressing et al. ""</ref><ref>Leslie A. Rogers ""</ref> Similar results are confirmed by other studies.<ref>Lauren M. Weiss, and Geoffrey W. Marcy. ""</ref><ref>Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard and Lars A. Buchhave. ""</ref><ref>Geoffrey W. Marcy et al. ""</ref> As for mass, the lower limit can vary widely for different planets depending on their compositions; the dividing mass can vary from as low as one to as high as 20 {{Earth mass}}. | ||
| Several ]s have been discovered that are possibly ]s, based on known masses and densities. For example, ] has a mass of 2.3 {{Earth mass}}, yet its density is the same as that of ], implying that it is a gas dwarf with a hydrogen–helium (or water vapor) atmosphere and only a small rocky core.<ref name=dangelo_bodenheimer_2016>{{cite journal|last=D'Angelo|first=G.|author2= Bodenheimer, P. |title=In Situ and Ex Situ Formation Models of Kepler 11 Planets|journal=The Astrophysical Journal|year=2016|volume=|issue=|pages=in press|doi=|arxiv = 1606.08088 |bibcode = 2016arXiv160608088D }}</ref> The even smaller ], having only roughly Earth's mass, is also suspected to be a gas planet due to its relatively large diameter (~20,500 km) and therefore low density.<ref>{{cite journal|url=http://www.nature.com/news/earth-mass-exoplanet-is-no-earth-twin-1.14477|title=Earth-mass exoplanet is no Earth twin : Nature News & Comment|last=Cowen|first=Ron|date=6 January 2014|journal=Nature|doi=10.1038/nature.2014.14477}}</ref> Such planets are not found orbiting too close to their parent stars, where their thick atmospheres would be evaporated by heat or blown away by ]s. It is demonstrated that the inner planets of the Kepler-11 system have higher densities than planets farther away. | Several ]s have been discovered that are possibly ]s, based on known masses and densities. For example, ] has a mass of 2.3 {{Earth mass}}, yet its density is the same as that of ], implying that it is a gas dwarf with a hydrogen–helium (or water vapor) atmosphere and only a small rocky core.<ref name=dangelo_bodenheimer_2016>{{cite journal|last=D'Angelo|first=G.|author2= Bodenheimer, P. |title=In Situ and Ex Situ Formation Models of Kepler 11 Planets|journal=The Astrophysical Journal|year=2016|volume=|issue=|pages=in press|doi=|arxiv = 1606.08088 |bibcode = 2016arXiv160608088D }}</ref> The even smaller ], having only roughly Earth's mass, is also suspected to be a gas planet due to its relatively large diameter (~20,500 km) and therefore low density.<ref>{{cite journal|url=http://www.nature.com/news/earth-mass-exoplanet-is-no-earth-twin-1.14477|title=Earth-mass exoplanet is no Earth twin : Nature News & Comment|last=Cowen|first=Ron|date=6 January 2014|journal=Nature|doi=10.1038/nature.2014.14477}}</ref> Such planets are not found orbiting too close to their parent stars, where their thick atmospheres would be evaporated by heat or blown away by ]s. It is demonstrated that the inner planets of the Kepler-11 system have higher densities than planets farther away. | ||
Revision as of 14:45, 13 November 2017
A mini-Neptune or sub-Neptune (sometimes known as a gas dwarf or transitional planet) is a planet of up to 10 Earth masses (ME), less massive than Uranus and Neptune, which have about 14.5 ME and 17 ME, respectively. Mini-Neptunes have thick hydrogen–helium atmospheres, probably with deep layers of ice, rock or liquid oceans (made of water, ammonia, a mixture of both, or heavier volatiles). These planets have small cores made of low-density volatiles.
Theoretical studies of such planets are loosely based on knowledge about Uranus and Neptune. Without a thick atmosphere, it would be classified as an ocean planet instead. An estimated dividing line between a rocky planet and a gaseous planet is around 1.6-2.0 Earth radii. Planets with larger radii and measured masses are mostly low-density and require an extended atmosphere to simultaneously explain their masses and radii, and empirical observations are showing that planets larger than approximately 1.6 Earth-radius (more massive than approximately 6 Earth-masses) contain significant amounts of volatiles or H–He gas (such planets appear to have a diversity of compositions that is not well-explained by a single mass–radius relation as that found in rocky planets). Similar results are confirmed by other studies. As for mass, the lower limit can vary widely for different planets depending on their compositions; the dividing mass can vary from as low as one to as high as 20 ME.
Several exoplanets have been discovered that are possibly gas dwarfs, based on known masses and densities. For example, Kepler-11f has a mass of 2.3 ME, yet its density is the same as that of Saturn, implying that it is a gas dwarf with a hydrogen–helium (or water vapor) atmosphere and only a small rocky core. The even smaller Kepler-138d, having only roughly Earth's mass, is also suspected to be a gas planet due to its relatively large diameter (~20,500 km) and therefore low density. Such planets are not found orbiting too close to their parent stars, where their thick atmospheres would be evaporated by heat or blown away by stellar winds. It is demonstrated that the inner planets of the Kepler-11 system have higher densities than planets farther away.
See also
References
- Optical to near-infrared transit observations of super-Earth GJ1214b: water-world or mini-Neptune?, E.J.W. de Mooij (1), M. Brogi (1), R.J. de Kok (2), J. Koppenhoefer (3,4), S.V. Nefs (1), I.A.G. Snellen (1), J. Greiner (4), J. Hanse (1), R.C. Heinsbroek (1), C.H. Lee (3), P.P. van der Werf (1),
- Architecture of Kepler's Multi-transiting Systems: II. New investigations with twice as many candidates, Daniel C. Fabrycky, Jack J. Lissauer, Darin Ragozzine, Jason F. Rowe, Eric Agol, Thomas Barclay, Natalie Batalha, William Borucki, David R. Ciardi, Eric B. Ford, John C. Geary, Matthew J. Holman, Jon M. Jenkins, Jie Li, Robert C. Morehead, Avi Shporer, Jeffrey C. Smith, Jason H. Steffen, Martin Still
- When Does an Exoplanet’s Surface Become Earth-Like?, blogs.scientificamerican.com, 20 June 2012
- Benjamin J. Fulton et al. "The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
- Courtney D. Dressing et al. "The Mass of Kepler-93b and The Composition of Terrestrial Planets"
- Leslie A. Rogers "Most 1.6 Earth-Radius Planets are not Rocky"
- Lauren M. Weiss, and Geoffrey W. Marcy. "The mass-radius relation for 65 exoplanets smaller than 4 Earth radii"
- Geoffrey W. Marcy, Lauren M. Weiss, Erik A. Petigura, Howard Isaacson, Andrew W. Howard and Lars A. Buchhave. "Occurrence and core-envelope structure of 1-4x Earth-size planets around Sun-like stars"
- Geoffrey W. Marcy et al. "Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets"
- D'Angelo, G.; Bodenheimer, P. (2016). "In Situ and Ex Situ Formation Models of Kepler 11 Planets". The Astrophysical Journal: in press. arXiv:1606.08088. Bibcode:2016arXiv160608088D.
- Cowen, Ron (6 January 2014). "Earth-mass exoplanet is no Earth twin : Nature News & Comment". Nature. doi:10.1038/nature.2014.14477.
- Six New Planets: Mini-Neptunes Found Around Sunlike Star, Victoria Jaggard, National Geographic News, Published February 2, 2011
- Barnes, Rory; Jackson, Brian; Raymond, Sean N.; West, Andrew A.; Greenberg, Richard (January 13, 2009). "The HD 40307 Planetary System: Super-Earths or Mini-Neptunes?". The Astrophysical Journal. 695 (2): 1006. arXiv:0901.1698. Bibcode:2009ApJ...695.1006B. doi:10.1088/0004-637X/695/2/1006.
