List of potentially habitable exoplanets

This is a list of potentially habitable exoplanets. The list is mostly 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 to various geophysical and geodynamical aspects, atmospheric density, radiation type and intensity, and the host star's plasma environment.[2]

Potential habitable zone status

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 favorable to Earth-like life. 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] In a 2020 journal-accepted preprint scientists published estimates of the occurrence rates of rocky habitable zone planets around Sun-like stars with updated data and criteria related to stellar effective temperature for habitable zones – including ∼4 such exoplanets around G and K dwarf stars within 10 pc of the Sun, ~300 million in the Milky Way and an average distance of the nearest HZ planet around G and K dwarfs about 6 pc.[8][9][10]

A 2015 review concluded that the exoplanets Kepler-62f, Kepler-186f and Kepler-442b were likely the best candidates for being potentially habitable.[11] These are at a distance of 1,200, 490 and 1,120 light-years away, respectively. Of these, Kepler-186f is closest in size to Earth, with 1.2 times Earth's radius, and it is located towards the outer edge of the habitable zone around its red dwarf host star. The potentially habitable planet TOI 700 d is only 100 light years away.[12]

In September 2020, astronomers identified 24 potential superhabitable planets (planets better than Earth), including unconfirmed planets, from among more than 4000 confirmed exoplanets at present, based on astrophysical parameters, as well as the natural history of known life forms on the Earth.[13]

List
This is a dynamic list and may never be able to satisfy particular standards for completeness. You can help by adding missing items with reliable sources.

This is a list of exoplanets within the habitable zone that are under 10 Earth masses/2.5 Earth radii. Note that this does not ensure habitability, and that * represents an unconfirmed planet or planet candidate. Earth is included for comparison.[14][1]

ObjectStarStar typeMass (M⊕)Radius (R⊕)Flux (F⊕)Teq (K)Period (days)Distance (ly) ESIRefs/Notes
EarthSun (Sol)G2V1.001.001.00255365.24— 1.00[14]
Teegarden's Star bTeegarden's StarM7V≥1.05—1.152644.9112.58 0.95[15]
TOI 700 dTOI 700M2V~1.721.140.8724637.4101 0.93
K2-72eK2-72M?V~2.211.291.1126124.2217 0.90 [16]
TRAPPIST-1dTRAPPIST-1M8V0.300.781.042584.0539 0.91Confirmed to be rocky[17][18]
Kepler-1649cKepler-1649M5V—1.060.7523719.5301 0.90 [19]
Proxima Centauri bProxima CentauriM5V≥1.27—0.7022811.1864.25 0.87[20]
Gliese 1061 dGliese 1061M5V≥1.64—0.6921813.012 0.86
Gliese 1061 cGliese 1061M5V≥1.74—1.452756.712 0.86
Ross 128 bRoss 128M4V≥1.40—1.482809.8711.03 0.86[21]
Luyten bLuyten's StarM3V≥2.89—1.0625818.6512.36 0.91[22]
TRAPPIST-1eTRAPPIST-1M8V0.770.910.672306.139 0.95Confirmed to be rocky[17][18]
Kepler-442bKepler-442K?V—1.350.70233112.31193 0.84[1]
Wolf 1061cWolf 1061M3V≥3.41—1.3027117.913.8 0.76 [1]
Gliese 667 CcGliese 667 CM1V≥3.81—0.8824728.123.62 0.85[23][1]
Kepler-1229bKepler-1229M?V—1.400.4921386.8865 0.73 [1]
TRAPPIST-1fTRAPPIST-1M8V0.931.050.382009.239 0.70Confirmed to be rocky[17][18]
Kepler-62fKepler-62K2V—1.410.41204267.3981 0.69[1][24]
Teegarden's Star cTeegarden's StarM7V≥1.11—0.3719911.412.58 0.68[15]
Kepler-186fKepler-186M1V—1.170.29188129.9579 0.64[1]
Tau Ceti fTau CetiG8V≥3.93—0.32190636.112 0.58 [1]
TRAPPIST-1gTRAPPIST-1M8V1.151.150.2618212.439 0.59Confirmed to be rocky[17][18]
Kapteyn b*Kapteyn's StarM1VI≥4.8—0.4320548.613 0.67Controversial[25]
Kepler-452b*Kepler-452G2V—1.631.11261384.81799 0.83Not confirmed[1][26][27]
Kepler-62eKepler-62K2V—1.611.15264122.4981 0.83[1][28]
Kepler-1652bKepler-1652M?V—1.600.8424438.1822
Kepler-1544bKepler-1544K2V—1.780.90248168.81092 [1]
Kepler-296eKepler-296K7V—1.521.5027634.1737 0.85[1][29]
Kepler-283cKepler-283K5V—1.820.9024892.71526 0.79[1]
K2-296bK2-296M?V—1.871.1526428.2519
Kepler-1410bKepler-1410K?V—1.781.3427460.91196
Kepler-1638bKepler-1638G4V—1.871.39276259.34973 [30]
Kepler-296fKepler-296K7V—1.800.6622563.3737 0.60[1][31]
Kepler-440bKepler-440K6V—1.911.44273101.1981 [1]
Kepler-705bKepler-705M?V—2.110.8324356.1903
Kepler-1653bKepler-1653K?V—2.171.04258140.32461
Gliese 832 cGliese 832M2V≥5.40—0.9925335.716 0.81[1]
Kepler-1606bKepler-1606G?V—2.071.41277196.42710 [32]
Kepler-1090bKepler-1090K0V—2.251.20267198.72800 [1]
Kepler-61bKepler-61K7V—2.151.3927359.91092 0.73[1][33]
Kepler-443bKepler-443K3V—2.350.89247177.72615 0.71[1]
Kepler-1701bKepler-1701K?V—2.221.37275169.11904 [1][34]
Kepler-22bKepler-22G5V—2.381.10261289.9635 [1][35]
LHS 1140 bLHS 1140M4V6.981.730.5021424.749 Confirmed to be rocky[36][37]
Kepler-1552bKepler-1552K?V—2.471.10261184.82507
K2-9bK2-9M2V—2.251.4527918.4270 [1][38]
Kepler-1540bKepler-1540K?V—2.490.92250125.4799
Gliese 180 c*Gliese 180M2V≥6.40—0.7823924.339 Not confirmed[1][39]
Kepler-1632bKepler-1632F?V—2.471.27270448.32337
Kepler-298dKepler-298K5V—2.501.2927177.51689 [1]
Gliese 163 cGliese 163M3V≥6.80—1.4127725.649 [1]
HD 40307 g*HD 40307K2V≥7.09—0.67226197.842 0.74Not confirmed[1][40]
K2-288BbK2-288 BM3V—1.910.4420731.4214
Gliese 3293 dGliese 3293M2V≥7.60—0.5922348.166 [1]
Gliese 229 AcGliese 229 AM1V≥7.27—0.53216122.018.8
Kepler-174dKepler-174K3V—2.190.43206247.41254 0.61[1]
Gliese 357 dGliese 357M2V≥6.10—0.3820055.731
Gliese 625 bGliese 625M2V2.82±0.5114.62821.3 [41]
Kepler-26e Kepler-26 K 2.1 46.8 1104 [42][43]

Previous candidates

Some exoplanet candidates detected by radial velocity that were originally thought to be potentially habitable were later found to most likely be artifacts of stellar activity. These include Gliese 581 d & g,[44] Gliese 667 Ce & f,[23] and Gliese 682 b & c.[39]

HD 85512 b was initially estimated to be potentially habitable,[45][46] but updated models for the boundaries of the habitable zone placed the planet interior to the HZ,[47][48] and it is now considered non-habitable.[1] Kepler-69c has gone through a similar process; though initially estimated to be potentially habitable,[49] it was quickly realized that the planet is more likely to be similar to Venus,[50] and is thus no longer considered habitable.[1]

Similarly, Tau Ceti e and f were initially both considered potentially habitable,[51] but with improved models of the circumstellar habitable zone, PHL currently only considers planet f potentially habitable.[1] Kepler-438b was also initially considered potentially habitable, with highest ESI of 0.88; however, it was later found to be a subject of powerful flares that can strip a planet of its atmosphere, so it is now considered non-habitable.[1] Gliese 180 b appears to be another example of a planet once considered potentially habitable but later found to be interior to the habitable zone.[1]

K2-3d and K2-18b were originally considered potentially habitable, and remain listed in the HEC,[1] but recent studies have shown them to be gaseous sub-Neptunes and thus unlikely to be habitable.[52][53][54][55][56][57]

KOI-1686.01 was also considered a potentially habitable exoplanet after its detection in 2011, until proven a false positive by NASA in 2015.[58] Several other KOIs were considered potentially habitable prior to confirmation, but with new data are no longer considered habitable.

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).[59]
Comparison of small planets found by Kepler in the habitable zone of their host stars.
Artist's impression of TOI-700 d
Artist's impression of Kepler-442b compared to Earth
Kepler-1229b as rendered by SpaceEngine
Star-planet distances and mass of the host star of roughly 4500 exoplanets and exoplanet candidates.
The temperatures of the stars are indicated with symbol colors; planetary radii are encoded in the symbol sizes.[13]

See also

Notes

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