Crossfield et al. (2016) reports the discovery of a planetary system of four Earth-size planets around the M-dwarf star K2-72. Up to two of these planets might be in the habitable zone. However, there are known corrections with the published values. We are waiting for additional results on this system to update the Habitable Exoplanet Catalog with the latest data.

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Click image for more details, or click here for larger version.

These are artistic representations of the top planets around other stars (exoplanets) with any potential to support liquid surface waterAll of them are larger than Earth and we are not certain about their composition and habitability yet. We only know that they seem to have the right size and orbit to support surface liquid water. They are ranked here from closest to farthest from Earth. This selection of objects of interest is subject to change as new interpretations or astronomical observations are made. Earth, Mars, Jupiter, and Neptune are shown for scale on the right.


Current Number of Potentially Habitable Exoplanets
Subterran
(Mars-size)

Terran
(Earth-size)
Superterran
(Super-Earth)
Total
0 13 29 42

subterran0.1 — 0.5 ME or 0.4 — 0.8 RE, terran0.5 — 5 ME or 0.8 — 1.5 RE, superterran5 — 10 ME or 1.5 — 2.5 REME = Earth masses, and RE = Earth radii.


Conservative Sample of Potentially Habitable Exoplanets


This is a list of the exoplanets that are more likely to have a rocky composition and maintain surface liquid water (i.e. 0.5 < Planet Radius ≤ 1.5 Earth radii or 0.1 < Planet Minimum Mass ≤ 5 Earth masses, and the planet is orbiting within the conservative habitable zone). They are represented artistically in the top image.

Name Type Mass
(ME)
Radius
(RE)
Flux
(SE)
Teq
(K)
Period
(days)
Distance
(ly)
ESI
001. GJ 667 C c M-Warm Terran ≥ 3.8 1.1 - 1.5 - 2.0 0.88 247 28.1 22 0.84
002. Kepler-442 b K-Warm Terran 8.2 - 2.3 - 1.0 1.3 0.70 233 112.3 1115 0.84
003. GJ 667 C f* M-Warm Terran ≥ 2.7 1.0 - 1.4 - 1.8 0.56 221 39.0 22 0.77
004. Wolf 1061 c M-Warm Terran ≥ 4.3 1.1 - 1.6 - 2.0 0.60 223 17.9 14 0.76
005. Kepler-1229 b (N) M-Warm Terran 9.8 - 2.7 - 1.2 1.4 0.49 213 86.8 769 0.73
006. Kapteyn b* M-Warm Terran ≥ 4.8 1.2 - 1.6 - 2.1 0.43 205 48.6 13 0.67
007. Kepler-62 f K-Warm Terran 10.2 - 2.8 - 1.2 1.4 0.39 201 267.3 1200 0.67
008. Kepler-186 f M-Warm Terran 4.7 - 1.5 - 0.6 1.2 0.29 188 129.9 561 0.61
009. GJ 667 C e* M-Warm Terran ≥ 2.7 1.0 - 1.4 - 1.8 0.30 189 62.2 22 0.60

* planet canditate/unconfirmed, (N) = new addition to the catalog


















Optimistic Sample of Potentially Habitable Exoplanets


This is a list of the exoplanets that are less likely to have a rocky composition or maintain surface liquid water (i.e. 1.5 < Planet Radius ≤ 2.5 Earth radii or 5 < Planet Minimum Mass ≤ 10 Earth masses, or the planet is orbiting within the optimistic habitable zone).

Name Type Mass
(ME)
Radius
(RE)
Flux
(SE)
Teq
(K)
Period
(days)
Distance
(ly)
ESI
001. Kepler-438 b M-Warm Terran 4.0 - 1.3 - 0.6 1.1 1.38 276 35.2 473 0.88
002. Kepler-296 e M-Warm Terran 12.5 - 3.3 - 1.4 1.5 1.22 267 34.1 737 0.85
003. Kepler-62 e K-Warm Superterran 18.7 - 4.5 - 1.9 1.6 1.10 261 122.4 1200 0.83
004. Kepler-452 b G-Warm Superterran 19.8 - 4.7 - 1.9 1.6 1.11 261 384.8 1402 0.83
005. GJ 832 c M-Warm Superterran ≥ 5.4 1.2 - 1.7 - 2.2 1.00 253 35.7 16 0.81
006. K2-3 d M-Warm Terran 11.1 1.5 1.46 280 44.6 137 0.80
007. Kepler-1544 b (N) K-Warm Superterran 31.7 - 6.6 - 2.6 1.8 0.90 248 168.8 1138 0.80
008. Kepler-283 c K-Warm Superterran 35.3 - 7.0 - 2.8 1.8 0.90 248 92.7 1741 0.79
009. tau Cet e* G-Warm Terran ≥ 4.3 1.1 - 1.6 - 2.0 1.51 282 168.1 12 0.78
010. Kepler-1410 b (N) K-Warm Superterran 31.7 - 6.6 - 2.6 1.8 1.34 274 60.9 1196 0.78
011. GJ 180 c* M-Warm Superterran ≥ 6.4 1.3 - 1.8 - 2.3 0.79 239 24.3 38 0.77
012. Kepler-1638 b (N) G-Warm Superterran 42.7 - 7.9 - 3.1 1.9 1.39 276 259.3 2866 0.76
013. Kepler-440 b K-Warm Superterran 41.2 - 7.7 - 3.1 1.9 1.43 273 101.1 851 0.75
014. GJ 180 b* M-Warm Superterran ≥ 8.3 1.3 - 1.9 - 2.4 1.23 268 17.4 38 0.75
015. Kepler-705 b (N) M-Warm Superterran ? - 12.7 - 4.8 2.1 0.83 243 56.1 818 0.74
016. HD 40307 g* K-Warm Superterran ≥ 7.1 1.3 - 1.8 - 2.3 0.68 227 197.8 42 0.74
017. GJ 163 c M-Warm Superterran ≥ 7.3 1.3 - 1.8 - 2.4 0.66 230 25.6 49 0.73
018. K2-18 b M-Warm Superterran ? - 16.5 - 6.0 2.2 0.94 251 32.9 111 0.73
019. Kepler-61 b K-Warm Superterran ? - 13.8 - 5.2 2.2 1.27 267 59.9 1063 0.73
020. Kepler-1606 b (N) G-Warm Superterran ? - 11.9 - 4.5 2.1 1.41 277 196.4 2869 0.73
021. Kepler-1090 b (N) G-Warm Superterran ? - 16.8 - 6.1 2.3 1.20 267 198.7 2289 0.72
022. Kepler-443 b K-Warm Superterran ? - 19.5 - 7.0 2.3 0.89 247 177.7 2540 0.71
023. Kepler-22 b G-Warm Superterran ? - 20.4 - 7.2 2.4 1.11 261 289.9 619 0.71
024. GJ 422 b* M-Warm Superterran ≥ 9.9 1.4 - 2.0 - 2.6 0.68 231 26.2 41 0.71
025. K2-9 b M-Warm Superterran ? - 16.8 - 6.1 2.2 1.38 276 18.4 359 0.71
026. Kepler-1552 b (N) K-Warm Superterran ? - 25.2 - 8.7 2.5 1.11 261 184.8 2015 0.70
027. GJ 3293 c* M-Warm Superterran ≥ 8.6 1.4 - 1.9 - 2.5 0.60 223 48.1 59 0.70
028. Kepler-1540 b (N) K-Warm Superterran ? - 26.2 - 9.0 2.5 0.92 250 125.4 854 0.70
029. Kepler-298 d K-Warm Superterran ? - 26.8 - 9.1 2.5 1.29 271 77.5 1545 0.68
030. Kepler-174 d K-Warm Superterran ? - 14.8 - 5.5 2.2 0.43 206 247.4 1174 0.61
031. Kepler-296 f M-Warm Superterran 28.7 - 6.1 - 2.5 1.8 0.34 194 63.3 737 0.60
032. GJ 682 c* M-Warm Superterran ≥ 8.7 1.4 - 1.9 - 2.5 0.37 198 57.3 17 0.59
033. KOI-4427 b* M-Warm Superterran 38.5 - 7.4 - 3.0 1.8 0.24 179 147.7 782 0.52

* planet canditate/unconfirmed, (N) = new addition to the catalog
















 


Tables Legend


  • Name - Name of the planet. This links to the data of the planet at the Extrasolar Planets Encyclopaedia or NASA Exoplanet Archive.
  • Type - PHL's classification of planets that includes host star spectral type (F, G, K, M), habitable zone location (hot, warm, cold) and size (miniterran, subterran, terran, superterran, jovian, neptunian) (e.g. Earth = G-Warm Terran, Venus = G-Hot Terran, Mars = G-Warm Subterran).
  • Mass - Minimum mass of the planet in Earth masses (Earth = 1.0 ME). Estimated for a pure iron, rocky, and water composition, respectively, when not available. 
  • Radius - Radius of planet in Earth radii (Earth = 1.0 RE). Estimated for a pure iron, rocky, and water composition, respectively, when not available.
  • Flux - Average stellar flux of the planet in Earth fluxes (Earth = 1.0 SE).
  • Teq - Equilibrium temperature in kelvins (K) assuming a 0.3 bond albedo (Earth = 255 K). Actual surface temperatures are expected to be larger than the equilibrium temperature depending on the atmosphere of the planets, which are currently unknown (e.g. Earth mean global surface temperature is about 288 K or 15°C).
  • Period - Orbital period in days (Earth = 365 days).
  • Distance - Distance from Earth in light years (ly).
  • ESI - Earth Similarity Index, a measure of similarity to Earth that summarizes how similar are these planets to the stellar flux, mass, and radius of Earth (Earth = 1.0). Results are sorted by this number. Planets more similar to Earth based on only these parameters are not necessarily more habitable.


The figure above shows all planets near the habitable zone (darker green shade is the conservative habitable zone and the lighter green shade is the optimistic habitable zone). Only those planets less than 10 Earth masses or 2.5 Earth radii are labeled. Some are still unconfirmed (* = unconfirmed). The different limits of the habitable zone are described in Kopparapu et al. (2014). Size of the circles corresponds to the radius of the planets (estimated from a mass-radius relationship when not available). Larger version here. Credit: PHL @ UPR Arecibo

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