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List of potentially habitable exoplanets

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This is a list of potentially habitable exoplanets and possible exoplanets. The list is based on estimates of habitability by the Habitable Exoplanets Catalog (HEC), and data from the NASA Exoplanet Archive. The HEC is maintained by the Planetary Habitability Laboratory at the University of Puerto Rico at Arecibo.[1]

Surface planetary habitability is thought to require orbiting at the right distance from the host star for liquid surface water to be present, in addition of various geophysical and geodynamical aspects, atmospheric density, radiation type and intensity, and the host star's plasma environment.[2]

Potential habitable zone status

Main article: Habitable zone

In astronomy and astrobiology, the circumstellar habitable zone (CHZ or sometimes "ecosphere", "liquid-water belt", "HZ", "life zone" or "Goldilocks zone") is the region around a star where a planet with sufficient atmospheric pressure can maintain liquid water on its surface.[3][4]

A potentially habitable planet implies a terrestrial planet within the circumstellar habitable zone and with conditions roughly comparable to those of Earth (i.e. an Earth analog) and thus potentially favourable to Earth-like life.[citation needed] However, the question of what makes a planet habitable is much more complex than having a planet located at the right distance from its host star so that water can be liquid on its surface: various geophysical and geodynamical aspects, the radiation, and the host star’s plasma environment can influence the evolution of planets and life, if it originated.[2]

In November 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way,[5][6] 11 billion of which may be orbiting Sun-like stars.[7]

A 2015 review concluded that the exoplanets Kepler-62f, Kepler-186f and Kepler-442b were likely the best candidates for being potentially habitable.[8] These are at a distance of 1,200, 490 and 1,120 light-years away, respectively. Of these, Kepler-186f is similar in size to Earth with a 1.2-Earth-radius measure and it is located towards the outer edge of the habitable zone around its red dwarf.

List from the Habitable Exoplanets Catalog

List of exoplanets in the conservative habitable zone

This is a list of the exoplanets that are more likely to have a rocky composition (which according to current research[9][10] requires a radius of less than 1.6 R⊕ and a mass less than 6 M⊕) and maintain surface liquid water (i.e. between 0.5 and 1.5 R⊕ and between 0.1 and 5 M⊕, and orbiting within the conservative habitable zone). Note that this does not ensure habitability, and that * represents an unconfirmed planet or planet candidate. Earth is included for comparison.

Object Star Star type Mass (M⊕) Radius (R⊕) Flux (F⊕) Teq (K) Period (days) Distance (ly) Ref
Earth Sun (Sol) G2V 1.00 1.00 1.00 255 365.24 -
Proxima Centauri b Proxima Centauri M6Ve ≥1.3 0.8 – 1.1 – 1.4 0.65 234 11.186 4.22 [11]
Gliese 667 Cc Gliese 667 C M3V ≥3.8 1.1 – 1.5 – 2.0 0.88 277 28.143 ± 0.029 23.62 [12][13]
Kepler-442b Kepler-442 K?V 8.2 – 2.3 – 1.0 1.34 0.70 233 112.3053 1291.6 [13]
Kepler-452b Kepler-452 G2V 19.8 – 4.7 – 1.9 1.50, 1.63 1.11 265+15
−13		 384.8 1402 [13][14]
Wolf 1061c Wolf 1061 M3V ≥ 4.3 1.1 – 1.6 – 2.0 0.60 223 17.9 13.8 [13]
Kepler-1229b Kepler-1229 M?V 9.8 – 2.7 – 1.2 1.4 0.49 213 86.8 769 [13]
Kapteyn b* Kapteyn sdM1 ≥ 4.8 1.2 - 1.6 - 2.1 0.43 205 48.6 13 [13]
Kepler-62f Kepler-62 K2V 10.2 – 2.8 – 1.2 1.41 0.39 244 267.291 1200 [13][15]
Kepler-186f Kepler-186 M1V 4.7 – 1.5 – 0.6 1.17 0.29 188 129.9459 561 [13]
Luyten b Luyten's Star M3.5V 3.15 - 2.89 - 2.63 1.06 206-293 18.650 12.36 [16]
TRAPPIST-1d TRAPPIST-1 M8V 0.30 0.78 1.04 258 4.05 39 [17][18]
TRAPPIST-1e TRAPPIST-1 M8V 0.77 0.91 0.67 230 6.1 39 [17][18]
TRAPPIST-1f TRAPPIST-1 M8V 0.93 1.046 0.38 200 9.2 39 [17][18]
TRAPPIST-1g TRAPPIST-1 M8V 1.15 1.15 0.26 182 12.4 39 [17][18]
LHS 1140 b LHS 1140 M?V 6.6 1.43 0.46 230 25 40 [19]
Kepler-1638b Kepler-1638 G4V 45 – 6 – 1 1.60 1.17 304 259.365 2491.83 [20]

List of exoplanets in the optimistic habitable zone

This is a list of the exoplanets that are less likely to have a rocky composition or maintain surface liquid water (i.e. 0.5 < planet's radius ≤ 1.5 Earth radii or 0.1 < planet's minimum mass ≤ 10 Earth masses, or the planet is orbiting within the optimistic habitable zone). Note that this does not ensure habitability, and that * represents an unconfirmed planet or planet candidate.

Object Star Star type Mass (M⊕) Radius (R⊕) Flux (F⊕) Teq (K) Period (days) Distance (ly) Ref
Kepler-438b Kepler-438 M?V 4.0 – 1.3 – 0.6 1.1 1.38 276 35.2 473 [13]
Kepler-296e Kepler-296 M?V 12.5 – 3.3 – 1.4 1.5 1.22 337.0±17.5 34.1 737 [13][21]
Kepler-62e Kepler-62 K2V 18.7 – 4.5 – 1.9 1.6 1.10 270±15 122.4 1200 [13][22]
Gliese 832 c Gliese 832 M2V ≥ 5.4 1.2 – 1.7 – 2.2 1.00 253; 233–280 35.7 16 [13]
K2-3d K2-3 M?V 11.1 1.5 1.46 300 44.6 137 [13][23]
Kepler-1544b Kepler-1544 K?V 31.7 - 6.6 - 2.6 1.8 0.90 248 168.8 1138 [13]
Kepler-283c Kepler-283 K?V 35.3 – 7.0 – 2.8 1.8 0.90 248 92.7 1741 [13]
Tau Ceti e* Tau Ceti G8.5V ≥ 4.3 1.1 – 1.6 – 2.0 1.51 282 168.1 12 [13]
Gliese 180 c Gliese 180 M2V ≥ 6.4 1.3 – 1.8 – 2.3 0.79 239 24.3 38 [13]
Kepler-440b Kepler-440 K?V 41.2 – 7.7 – 3.1 1.9 1.43 273 101.1 851 [13]
Gliese 180 b Gliese 180 M2V ≥ 8.3 1.3 – 1.9 – 2.4 1.23 268 17.4 38 [13]
HD 40307 g HD 40307 K2.5V ≥ 7.1 1.3 – 1.8 – 2.3 0.68 227 197.8 42 [13]
Gliese 163 c Gliese 163 M3.5V ≥ 7.3 1.3 – 1.8 – 2.3 0.66 230; 277 25.6 49 [13]
K2-18b K2-18 M?V ? – 16.5 – 6.0 2.2 0.94 272±15 32.9 111 [13][24]
Kepler-61b Kepler-61 K7V ? – 13.8 – 5.2 2.2 1.27 258, 273±13 59.9 1063 [13][25]
Kepler-443b Kepler-443 K?V ? – 19.5 – 7.0 2.3 0.89 247 177.7 2540 [13]
Kepler-22b Kepler-22 G5V ? – 20.4 – 7.2 2.04; 2.4 1.11 262 289.9 619 [13][26]
Gliese 422 b* Gliese 422 M3.5V ≥ 9.9 1.4 – 2.0 – 2.6 0.68 231 26.2 41 [13]
K2-9b K2-9 M?V ? – 16.8 – 6.1 2.2 1.38 284±14, 314+67
−64		 18.4 359 [13][27]
Gliese 3293 c Gliese 3293 M2.5V ≥ 8.6 1.4 – 1.9 – 2.5 0.60 223 48.1 59 [13]
Kepler-298d Kepler-298 K?V ? – 26.8 – 9.1 2.5 1.29 271 77.5 1545 [13]
Kepler-174d Kepler-174 K?V ? – 14.8 – 5.5 2.2 0.43 206 247.4 1174 [13]
Kepler-296f Kepler-296 M?V 28.7 – 6.1 – 2.5 1.8 0.34 198, 274.0±15.0 63.3 737 [13][28]
Gliese 682 c Gliese 682 M3.5V ≥ 8.7 1.4 – 1.9 – 2.5 0.37 198 57.3 17 [13]
KOI-4427 b* KOI-4427 M?V 38.5 – 7.4 – 3.0 1.8 0.24 179 147.7 782 [13]
Kepler-1090b Kepler-1090 G?V ? – 16.8 – 6.1 2.3 1.20 267 198.7 2289 [13]
Ross 128 b Ross 128 M4V ≥1.5 ~1.1 1.38 280 9.8658 (± 0.0070) 11.03 [29]
HD 20794 e* 82 G. Eridani G8V 4.77+0.96
−0.86		 331.41 20 [30]
Gliese 625 b Gliese 625 M2V 2.82±0.51 14.628 21.3 [31]
HD 219134 g* HD 219134 K3V >10.81 1.5 - 2.4 - 3.0 ? 298 94.2 21.35 [32]

Previous candidates

HD 85512 b was initially estimated to be potentially habitable,[33][34] but updated models for the boundaries of the habitable zone placed the planet within the HZ,[35][36] and it is now considered non-habitable.[13] Kepler-69c has gone through a similar process; though initially estimated to be potentially habitable,[37] it was quickly realized that the planet is more likely to be similar to Venus,[38] and is thus no longer considered habitable.[13]

Similarly, Tau Ceti f was initially considered potentially habitable,[39] but the improved model of the circumstellar habitable zone places the planet exterior to the outer limits of habitability, so it is now considered non-habitable.[13]

KOI-1686.01 was also considered a potentially habitable exoplanet after its detection in 2011, until proven a false positive by NASA in 2015.[40]

Notable exoplanets – Kepler Space Telescope
Confirmed small exoplanets in habitable zones.
(Kepler-62e, Kepler-62f, Kepler-186f, Kepler-296e, Kepler-296f, Kepler-438b, Kepler-440b, Kepler-442b)
(Kepler Space Telescope; 6 January 2015).[41]
Comparison of small planets found by Kepler in the habitable zone of their host stars.

See also

References

  1. ^ "Habitable Exoplanets Catalog". University of Puerto Rico at Arecibo. 2015. Retrieved 3 June 2015.
  2. ^ a b Lammer, H.; Bredehöft, J. H.; Coustenis, A.; Khodachenko, M. L.; et al. (2009). "What makes a planet habitable?" (PDF). The Astronomy and Astrophysics Review. 17: 181–249. Bibcode:2009A&ARv..17..181L. doi:10.1007/s00159-009-0019-z. Archived from the original (PDF) on 2016-06-02. Retrieved 2016-05-03. {{cite journal}}: Unknown parameter |deadurl= ignored (|url-status= suggested) (help)
  3. ^ "VPL Glossary". washington.edu.
  4. ^ "The Goldilocks Zone". NASA. 2 October 2003.
  5. ^ Overbye, Dennis (4 November 2013). "Far-Off Planets Like the Earth Dot the Galaxy". New York Times. Retrieved 5 November 2013.
  6. ^ Petigura, Erik A.; et al. (31 October 2013). "Prevalence of Earth-size planets orbiting Sun-like stars". Proceedings of the National Academy of Sciences of the United States of America. 110: 19273–19278. arXiv:1311.6806. Bibcode:2013PNAS..11019273P. doi:10.1073/pnas.1319909110. PMC 3845182. PMID 24191033. Retrieved 5 November 2013.
  7. ^ Khan, Amina (4 November 2013). "Milky Way may host billions of Earth-size planets". Los Angeles Times. Retrieved 5 November 2013.
  8. ^ Gilster, Paul; LePage, Andrew (30 January 2015). "A Review of the Best Habitable Planet Candidates". Centauri Dreams, Tau Zero Foundation. Retrieved 24 July 2015.
  9. ^ Gilster, Paul; LePage, Andrew (14 November 2014). "The Transition from Rocky to Non-Rocky Planets". Centauri Dreams, Tau Zero Foundation. Retrieved 17 October 2017.
  10. ^ LePage, Andrew (3 January 2015). "The Composition of Super-Earths". Drew Ex Machina. Retrieved 17 October 2017.
  11. ^ Anglada-Escudé, Guillem; et al. (2016). "A terrestrial planet candidate in a temperate orbit around Proxima Centauri" (PDF). Nature. 536 (7617): 437–440. arXiv:1609.03449. Bibcode:2016Natur.536..437A. doi:10.1038/nature19106. ISSN 0028-0836. PMID 27558064.
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  18. ^ a b c d Grimm, Simon L.; Demory, Brice-Olivier; Gillon, Michael; Dorn, Caroline; Agol, Eric; Burdanov, Artem; Delrez, Laetitia; Sestovic, Marko; Triaud, Amaury H.M.J.; Turbet, Martin; Bolmont, Emeline; Caldas, Anthony; de Wit, Julien; Jehin, Emmanuel; Leconte, Jeremy; Raymond, Sean N.; Van Grootel, Valerie; Burgasser, Adam J.; Carey, Sean; Fabrycky, Daniel; Heng, Kevin; Hernandez, David M.; Ingalls, James G.; Lederer, Susan; Selsis, Franck; Queloz, Didier (5 February 2018). "The nature of the TRAPPIST-1 exoplanets". arXiv:1802.01377 [astro-ph.EP].
  19. ^ Dickinson, David (19 April 2017). "Welcome to LHS 1140b: A Super-Earth in the Habitable Zone". Sky & Telescope. Retrieved 17 October 2017.
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  21. ^ "Confirmed Planet Overview Page: Kepler-296e". NASA Exoplanet Archive. NASA Exoplanet Science Institute. Retrieved 4 June 2016.
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  23. ^ "Confirmed Planet Overview Page: K2-3d". NASA Exoplanet Archive. NASA Exoplanet Science Institute. Retrieved 4 June 2016.
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  29. ^ Wenz, John (15 November 2017). "A potentially habitable planet has been discovered just 11 light-years away". Astronomy. Retrieved 19 November 2017.
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  32. ^ "Confirmed Planet Overview Page: HD 219134 g". NASA Exoplanet Archive. NASA Exoplanet Science Institute. Retrieved 14 February 2018.
  33. ^ Kaltenegger, L.; et al. (2011). "A Habitable Planet around HD 85512?". arXiv:1108.3561. Bibcode:2011arXiv1108.3561K. {{cite journal}}: Cite journal requires |journal= (help)
  34. ^ Mendez, Abel (1 August 2012). "Five Potential Habitable Exoplanets Now" (Press release). Planetary Habitability Laboratory @ UPR Arecibo. Retrieved 4 June 2015.
  35. ^ Kopparapu, Ravi Kumar; et al. (2013). "Habitable Zones Around Main-Sequence Stars: New Estimates". The Astrophysical Journal. 765: 131. arXiv:1301.6674. Bibcode:2013ApJ...765..131K. doi:10.1088/0004-637X/765/2/131.
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  37. ^ Barclay, Thomas; et al. (2013). "A super-Earth-sized planet orbiting in or near the habitable zone around Sun-like star". The Astrophysical Journal. 768: 101. arXiv:1304.4941. Bibcode:2013ApJ...768..101B. doi:10.1088/0004-637X/768/2/101.
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