List of potentially habitable exoplanets

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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[edit]

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 2021 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[edit]

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]

Object Star Star type Mass (M) Radius (R) Flux (F) Teq (K) Period (days) Distance (ly) Refs/Notes
Earth Sun (Sol) G2V 1.00 1.00 1.00 255 365.24 [14]
Teegarden's Star b Teegarden's Star M7V ≥1.05 1.15 264 4.91 12.58 [15]
TOI 700 d TOI 700 M2V ~1.72 1.14 0.87 246 37.4 101
K2-72e K2-72 M?V ~2.21 1.29 1.11 261 24.2 217 [16]
TRAPPIST-1d TRAPPIST-1 M8V 0.30 0.78 1.04 258 4.05 39 Confirmed to be rocky[17][18]
Kepler-1649c Kepler-1649 M5V 1.06 0.75 237 19.5 301 [19]
Proxima Centauri b Proxima Centauri M5V ≥1.27 0.70 228 11.186 4.25 [20]
Gliese 1061 d Gliese 1061 M5V ≥1.64 0.69 218 13.0 12
Gliese 1061 c Gliese 1061 M5V ≥1.74 1.45 275 6.7 12
Ross 128 b Ross 128 M4V ≥1.40 1.48 280 9.87 11.03 [21]
Luyten b Luyten's Star M3V ≥2.89 1.06 258 18.65 12.36 [22]
TRAPPIST-1e TRAPPIST-1 M8V 0.77 0.91 0.67 230 6.1 39 Confirmed to be rocky[17][18]
Kepler-442b Kepler-442 K?V 1.35 0.70 233 112.3 1193 [1]
Wolf 1061c Wolf 1061 M3V ≥3.41 1.30 271 17.9 13.8 [1]
Gliese 667 Cc Gliese 667 C M1V ≥3.81 0.88 247 28.1 23.62 [23][1]
Kepler-1229b Kepler-1229 M?V 1.40 0.49 213 86.8 865 [1]
TRAPPIST-1f TRAPPIST-1 M8V 0.93 1.05 0.38 200 9.2 39 Confirmed to be rocky[17][18]
Kepler-62f Kepler-62 K2V 1.41 0.41 204 267.3 981 [1][24]
Teegarden's Star c Teegarden's Star M7V ≥1.11 0.37 199 11.4 12.58 [15]
Kepler-186f Kepler-186 M1V 1.17 0.29 188 129.9 579 [1]
Tau Ceti f Tau Ceti G8V ≥3.93 0.32 190 636.1 12 [1]
TRAPPIST-1g TRAPPIST-1 M8V 1.15 1.15 0.26 182 12.4 39 Confirmed to be rocky[17][18]
Kapteyn b* Kapteyn's Star M1VI ≥4.8 0.43 205 48.6 13 Controversial[25]
Kepler-452b* Kepler-452 G2V 1.63 1.11 261 384.8 1799 Not confirmed[1][26][27]
Kepler-62e Kepler-62 K2V 1.61 1.15 264 122.4 981 [1][28]
Kepler-1652b Kepler-1652 M?V 1.60 0.84 244 38.1 822
Kepler-1544b Kepler-1544 K2V 1.78 0.90 248 168.8 1092 [1]
Kepler-296e Kepler-296 K7V 1.52 1.50 276 34.1 737 [1][29]
Kepler-283c Kepler-283 K5V 1.82 0.90 248 92.7 1526 [1]
K2-296b EPIC 201238110] M?V 1.87 1.15 264 28.2 519
Kepler-1410b Kepler-1410 K?V 1.78 1.34 274 60.9 1196
Kepler-1638b Kepler-1638 G4V 1.87 1.39 276 259.3 4973 [30]
Kepler-296f Kepler-296 K7V 1.80 0.66 225 63.3 737 [1][31]
Kepler-440b Kepler-440 K6V 1.91 1.44 273 101.1 981 [1]
Kepler-705b Kepler-705 M?V 2.11 0.83 243 56.1 903
Kepler-1653b Kepler-1653 K?V 2.17 1.04 258 140.3 2461
Gliese 832 c Gliese 832 M2V ≥5.40 0.99 253 35.7 16 [1]
Kepler-1606b Kepler-1606 G?V 2.07 1.41 277 196.4 2710 [32]
Kepler-1090b Kepler-1090 K0V 2.25 1.20 267 198.7 2800 [1]
Kepler-61b Kepler-61 K7V 2.15 1.39 273 59.9 1092 [1][33]
Kepler-443b Kepler-443 K3V 2.35 0.89 247 177.7 2615 [1]
Kepler-1701b Kepler-1701 K?V 2.22 1.37 275 169.1 1904 [1][34]
Kepler-22b Kepler-22 G5V 2.38 1.10 261 289.9 635 [1][35]
LHS 1140 b LHS 1140 M4V 6.98 1.73 0.50 214 24.7 49 Confirmed to be rocky[36][37]
Kepler-1552b Kepler-1552 K?V 2.47 1.10 261 184.8 2507
K2-9b K2-9 M2V 2.25 1.45 279 18.4 270 [1][38]
Kepler-1540b Kepler-1540 K?V 2.49 0.92 250 125.4 799
Gliese 180 c* Gliese 180 M2V ≥6.40 0.78 239 24.3 39 Not confirmed[1][39]
Kepler-1632b Kepler-1632 F?V 2.47 1.27 270 448.3 2337
Kepler-298d Kepler-298 K5V 2.50 1.29 271 77.5 1689 [1]
Gliese 163 c Gliese 163 M3V ≥6.80 1.41 277 25.6 49 [1]
HD 40307 g* HD 40307 K2V ≥7.09 0.67 226 197.8 42 Not confirmed[1][40]
K2-288Bb K2-288 B M3V 1.91 0.44 207 31.4 214
Gliese 3293 d Gliese 3293 M2V ≥7.60 0.59 223 48.1 66 [1]
Gliese 229 Ac Gliese 229 A M1V ≥7.27 0.53 216 122.0 18.8
Kepler-174d Kepler-174 K3V 2.19 0.43 206 247.4 1254 [1]
Gliese 357 d Gliese 357 M2V ≥6.10 0.38 200 55.7 31
Gliese 625 b Gliese 625 M2V 2.82±0.51 14.628 21.3 [41]
Kepler-26e Kepler-26 K 2.1 46.8 1104 [42][43]

Previous candidates[edit]

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.

Gallery[edit]

Notable exoplanetsKepler Space Telescope
KeplerExoplanets-NearEarthSize-HabitableZone-20150106.png
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]
PIA19827-Kepler-SmallPlanets-HabitableZone-20150723.jpg
Comparison of small planets found by Kepler in the habitable zone of their host stars.
PIA23408-Exoplanet-TOI700d-20200106.jpg
Artist's impression of TOI-700 d
Kepler442b(comp).jpg
Artist's impression of Kepler-442b compared to Earth
Kepler-1229b.jpg
Kepler-1229b as rendered by SpaceEngine
Images large ast.2019.2161 figure1.jpg
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[edit]

Notes[edit]

References[edit]

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