Astronomy:Small planet radius gap
The small planet radius gap (also called the Fulton gap,[1] photoevaporation valley,[2][3] or Sub-Neptune Desert[4]) is an observed scarcity of planets with radii between 1.5 and 2 times Earth's radius, likely due to photoevaporation-driven mass loss.[5][6][7] A bimodality in the Kepler exoplanet population was first observed in 2011[8] and attributed to the absence of significant gas atmospheres on close-in, low-mass planets. This feature was noted as possibly confirming an emerging hypothesis that photoevaporation could drive atmospheric mass loss[5][9] This would lead to a population of bare, rocky cores with smaller radii at small separations from their parent stars, and planets with thick hydrogen- and helium-dominated envelopes with larger radii at larger separations.[5][9] The bimodality in the distribution was confirmed with higher-precision data in the California-Kepler Survey in 2017,[6][1] which was shown to match the predictions of the photoevaporative mass-loss hypothesis later that year.[7]
Despite the implication of the word 'gap', the Fulton gap does not actually represent a range of radii completely absent from the observed exoplanet population, but rather a range of radii that appear to be relatively uncommon.[6] As a result, 'valley' is often used in place of 'gap'.[2][3][7] The specific term "Fulton gap" is named for Benjamin J. Fulton, whose doctoral thesis included precision radius measurements that confirmed the scarcity of planets between 1.5 and 2 Earth radii, for which he won the Robert J. Trumpler Award,[10][11] although the existence of this radius gap had been noted along with its underlying mechanisms as early as 2011,[8] 2012[9] and 2013.[5]
Within the photoevaporation model of Owen and Wu, the radius gap arises as planets with H/He atmospheres that double the core's radius are the most stable to atmospheric mass-loss. Planets with atmospheres larger than this are vulnerable to erosion and their atmospheres evolve towards a size that doubles the core's radius. Planets with smaller atmospheres undergo runaway loss, leaving them with no H/He dominated atmosphere.[7]
Other possible explanations
- Runaway gas accretion by larger planets.[12]
- Observational bias favoring easier detection of hot ocean planets with extended steam atmospheres.[13]
See also
References
- ↑ 1.0 1.1 Boyle, Rebecca (2019-05-16). "As Planet Discoveries Pile Up, a Gap Appears in the Pattern". Quanta Magazine. https://www.quantamagazine.org/as-planet-discoveries-pile-up-a-gap-appears-in-the-pattern-20190516/.
- ↑ 2.0 2.1 Van Eylen, V; Agentoft, Camilla; Lundkvist, M S; Kjeldsen, H; Owen, J E; Fulton, B J; Petigura, E; Snellen, I (2018-07-06). "An asteroseismic view of the radius valley: stripped cores, not born rocky". Monthly Notices of the Royal Astronomical Society (Oxford University Press (OUP)) 479 (4): 4786–4795. doi:10.1093/mnras/sty1783. ISSN 0035-8711.
- ↑ 3.0 3.1 Armstrong, David J.; Meru, Farzana; Bayliss, Daniel; Kennedy, Grant M.; Veras, Dimitri (2019-07-17). "A Gap in the Mass Distribution for Warm Neptune and Terrestrial Planets". The Astrophysical Journal (American Astronomical Society) 880 (1): L1. doi:10.3847/2041-8213/ab2ba2. ISSN 2041-8213. Bibcode: 2019ApJ...880L...1A.
- ↑ McDonald, George D.; Kreidberg, Laura; Lopez, Eric (2019-04-29). "The Sub-Neptune Desert and Its Dependence on Stellar Type: Controlled by Lifetime X-Ray Irradiation". The Astrophysical Journal (American Astronomical Society) 876 (1): 22. doi:10.3847/1538-4357/ab1095. ISSN 1538-4357. Bibcode: 2019ApJ...876...22M.
- ↑ 5.0 5.1 5.2 5.3 Owen, James E.; Wu, Yanqin (2013-09-12). "KEPLER PLANETS: A TALE OF EVAPORATION". The Astrophysical Journal (IOP Publishing) 775 (2): 105. doi:10.1088/0004-637x/775/2/105. ISSN 0004-637X. Bibcode: 2013ApJ...775..105O.
- ↑ 6.0 6.1 6.2 Fulton, Benjamin J.; Petigura, Erik A.; Howard, Andrew W.; Isaacson, Howard; Marcy, Geoffrey W.; Cargile, Phillip A.; Hebb, Leslie; Weiss, Lauren M. et al. (2017-08-24). "The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets". The Astronomical Journal 154 (3): 109. doi:10.3847/1538-3881/aa80eb. ISSN 1538-3881. Bibcode: 2017AJ....154..109F.
- ↑ 7.0 7.1 7.2 7.3 Owen, James E.; Wu, Yanqin (2017-09-20). "The Evaporation Valley in the Kepler Planets". The Astrophysical Journal (American Astronomical Society) 847 (1): 29. doi:10.3847/1538-4357/aa890a. ISSN 1538-4357. Bibcode: 2017ApJ...847...29O.
- ↑ 8.0 8.1 Youdin, Andrew N. (2011-11-20). "THE EXOPLANET CENSUS: A GENERAL METHOD APPLIED TO KEPLER". The Astrophysical Journal 742 (1): 38. doi:10.1088/0004-637X/742/1/38. ISSN 0004-637X. Bibcode: 2011ApJ...742...38Y. https://iopscience.iop.org/article/10.1088/0004-637X/742/1/38.
- ↑ 9.0 9.1 9.2 Lopez, Eric D.; Fortney, Jonathan J.; Miller, Neil (2012-11-21). "How Thermal Evolution and Mass-Loss Sculpt Populations of Super-Earths and Sub-Neptunes: Application to the Kepler-11 System and Beyond". The Astrophysical Journal (IOP Publishing) 761 (1): 59. doi:10.1088/0004-637x/761/1/59. ISSN 0004-637X. Bibcode: 2012ApJ...761...59L.
- ↑ "BJ Fulton Wins 2018 Robert J. Trumpler Award for 'Landmark' Exoplanet Discovery Using Keck Observatory". 2018-09-10. http://www.keckobservatory.org/fulton_gap/.
- ↑ "IfA graduate receives prestigious award for work on extrasolar planets". 2018-08-15. https://www.hawaii.edu/news/2018/08/15/benjamin-fulton-recognition/.
- ↑ Venturini, Julia; Helled, Ravit (17 October 2017). "The Formation of Mini-Neptunes". The Astrophysical Journal 848 (2): 95. doi:10.3847/1538-4357/aa8cd0. Bibcode: 2017ApJ...848...95V.
- ↑ Mousis, Olivier; Deleuil, Magali; Aguichine, Artyom; Marcq, Emmanuel; Naar, Joseph; Lorena Acuña Aguirre; Brugger, Bastien; Goncalves, Thomas (2020). "Irradiated Ocean Planets Bridge Super-Earth and Sub-Neptune Populations". The Astrophysical Journal 896 (2): L22. doi:10.3847/2041-8213/ab9530. Bibcode: 2020ApJ...896L..22M.
 |  |
