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List of potentially habitable exoplanets

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Title: List of potentially habitable exoplanets  
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Subject: Earth Similarity Index, Kepler-62f, Kepler-62e, Gliese 667 Cc, List of nearest terrestrial exoplanet candidates
Collection: Exoplanets in the Habitable Zone, Lists of Exoplanets
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List of potentially habitable exoplanets

Artist's impression of Kepler-22b, a large "Super-Earth" within its star's habitable zone.

This is a list of potentially habitable exoplanets candidates ranked by similarity with Earth using the Earth Similarity Index. The list is based on methodology and estimations provided by the Habitable Exoplanets Catalog, which is maintained by the Planetary Habitability Laboratory at UPR-Arecibo.

Contents

  • Potential habitable zone status 1
  • List from the Habitable Exoplanets Catalog 2
    • Key 2.1
    • Table 2.2
  • Previous candidates 3
  • See also 4
  • References 5
  • External links 6

Potential habitable zone status

Artist's impression of Gliese 581 d, a previously secure but now dubious potentially habitable exoplanet

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.[1][2]

A potentially habitable planet implies a terrestrial planet within the CHZ and with conditions roughly comparable to those of Earth (i.e. an Earth analog) and thus potentially favourable to life.

Although only about a dozen planets have been confirmed in the habitable zone, the Kepler spacecraft has identified a further 54 candidates and current estimates indicate that there are at least 8.8 billion Earth-sized planets capable of life in habitable zones of Sun-like stars in the Milky Way.[3]

On 4 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,[4][5] 11 billion of which may be orbiting Sun-like stars.[6] The nearest such planet could be 12 light-years away, according to the scientists.[4][5]

List from the Habitable Exoplanets Catalog

The data in the following table is from the Habitable Exoplanets Catalog.[7] This habitability index does not take into account the differences in the habitability of certain types of stars and star systems, such as red dwarfs and binary star systems. See habitability of red dwarf systems for more information.

Key

The planets listed below are evaluated on seven different criteria:

  • Earth Similarity Index (ESI) — Similarity to Earth on a scale from 0 to 1, with 1 being the most Earth-like. ESI depends on the planet's radius, density, escape velocity, and surface temperature.
  • Standard Primary Habitability (SPH) — Suitability for vegetation on a scale from 0 to 1, with 1 being best-suited for growth. SPH depends on surface temperature (and relative humidity if known).
  • Habitable Zone Distance (HZD) — Distance from the center of the star's habitable zone, scaled so that –1 represents the inner edge of the zone, and +1 represents the outer edge. HZD depends on the star's luminosity and temperature and the size of the planet's orbit.
  • Habitable Zone Composition (HZC) — Measure of bulk composition, where values close to zero are likely iron–rock–water mixtures. Values below –1 represent bodies likely composed mainly of iron, and values greater than +1 represent bodies likely composed mainly of gas. HZC depends on the planet's mass and radius.
  • Habitable Zone Atmosphere (HZA) — Potential for the planet to hold a habitable atmosphere, where values below –1 represent bodies likely with little or no atmosphere, and values above +1 represent bodies likely with thick hydrogen atmospheres (e.g. gas giants). Values between –1 and +1 are more likely to have atmospheres suitable for life, though zero is not necessarily ideal. HZA depends on the planet's mass, radius, orbit size, and the star's luminosity.
  • Planetary Class (pClass) — Classifies objects based on thermal zone (hot, warm, or cold, where warm is in the habitable zone) and mass (asteroidan, mercurian, subterran, terran, superterran, neptunian, and jovian).
  • Habitable Class (hClass) — Classifies habitable planets based on temperature: hypopsychroplanets (hP) = very cold (< −50 °C); psychroplanets (P) = cold; mesoplanets (M) = medium-temperature (0–50 °C; not to be confused with the other definition of mesoplanets); thermoplanets (T) = hot; hyperthermoplanets (hT) = very hot (> 100 °C). Mesoplanets would be ideal for complex life, whereas class hP or hT would only support extremophilic life. Non-habitable planets are simply given the class NH.

Table

(For comparison purposes, the four solar terrestrial planets are included in this list)

Name ESI SPH HZD HZC HZA pClass hClass Distance (ly) Status Year of
discovery
0N/A !Earth 1.00 0.72 −0.50 −0.31 −0.52 warm terran mesoplanet 0 non-exoplanet prehistoric
1 KOI-3010.01 0.96 0.93 −0.88 −0.16 −0.06 warm superterran mesoplanet 1213.4[8] Kepler candidate 2011
2 KOI-3284.01 0.90 0.88 −0.93 −0.14 −0.73 warm terran mesoplanet 1218.0 Kepler candidate 2011
3 KOI-1686.01 0.89 0.42 −0.63 −0.16 −0.13 warm superterran mesoplanet 1033.8 Kepler candidate 2011
4 Gliese 667 Cc 0.84 0.64 −0.62 −0.15 +0.21 warm superterran mesoplanet 23.6 Confirmed 2011
5 KOI-4742.01 0.83 0.98 −0.72 −0.15 +0.28 warm superterran mesoplanet 1291.6 Kepler candidate 2011
6 Kepler-62e 0.83 0.96 −0.70 −0.15 +0.28 warm superterran mesoplanet 1199.7 Confirmed 2013
7 Gliese 832 c 0.81 0.96 −0.72 −0.15 +0.43 warm superterran mesoplanet 16.1 Confirmed 2014
8 Kepler-283c 0.79 0.85 −0.58 −0.14 +0.69 warm superterran mesoplanet 1496.8 Confirmed 2011
9 KOI-2418.01 0.79 0.00 −0.40 −0.15 +0.44 warm superterran psychroplanet 996.9 Kepler candidate 2011
10 KOI-2529.02 0.79 0.33 −0.87 −0.14 +0.47 warm superterran mesoplanet 1339.4 Kepler candidate 2011
11 Tau Ceti e 0.78 0.00 −0.92 −0.15 +0.16 warm superterran mesoplanet 11.9 Unconfirmed 2012
12 Kepler-296f 0.78 0.15 −0.90 −0.14 +0.53 warm superterran mesoplanet 1089.6 Confirmed 2011
13 Gliese 180 c 0.77 0.42 −0.53 −0.14 +0.64 warm superterran mesoplanet 39.5 Unconfirmed 2014
14 Gliese 581 g 0.76 0.96 −0.70 −0.15 +0.28 warm superterran psychroplanet 20.2 dubious 2010
15 KOI-2474.01 0.76 0.00 −0.93 −0.15 +0.25 warm superterran mesoplanet 1605.7 Kepler candidate 2011
16 Gliese 667 Cf 0.77 0.00 −0.22 −0.16 +0.08 warm superterran psychroplanet 23.6 dubious 2013
17 KOI-2469.01 0.76 0.71 −0.75 −0.13 +0.99 warm superterran mesoplanet 1556.8 Kepler candidate 2011
18 KOI-2992.01 0.76 0.52 −0.54 −0.13 +1.06 warm superterran mesoplanet 1375.4 Kepler candidate 2011
19 KOI-4333.01 0.75 0.00 −0.90 −0.15 +0.32 warm superterran thermoplanet 2504.7 Kepler candidate 2011
20 Gliese 163 c 0.75 0.02 −0.96 −0.14 +0.58 warm superterran mesoplanet 48.9 Confirmed 2012
21 Gliese 180 b 0.75 0.41 −0.88 −0.14 +0.74 warm superterran mesoplanet 39.5 Unconfirmed 2014
22 HD 40307 g 0.74 0.04 −0.23 −0.14 +0.77 warm superterran psychroplanet 41.7 Confirmed 2012
23 KOI-854.01 0.74 1.00 −0.72 −0.13 +1.39 warm superterran mesoplanet 1077.7 Kepler candidate 2011
24 KOI-4550.01 0.74 1.00 −0.82 −0.13 +0.97 warm superterran mesoplanet 1847.5 Kepler candidate 2011
25 Kepler-61b 0.73 0.27 −0.88 −0.13 +1.24 warm superterran mesoplanet 1062.8 Confirmed 2013
26 KOI-4745.01 0.73 0.91 −0.49 −0.13 +1.44 warm superterran mesoplanet 2564.4 Kepler candidate 2011
27 KOI-2762.01 0.73 0.10 −0.27 −0.14 +1.01 warm superterran mesoplanet 1169.5 Kepler candidate 2011
28 KOI-1871.01 0.72 0.27 −0.88 −0.12 +1.34 warm superterran mesoplanet 1176.7 Kepler candidate 2011
29 KOI-4036.01 0.72 0.99 −0.77 −0.12 +1.49 warm superterran mesoplanet 1135.0 Kepler candidate 2011
30 Gliese 422 b 0.71 0.17 −0.41 −0.13 +1.11 warm superterran mesoplanet 41.3 Unconfirmed 2014
31 Kepler-22b 0.71 0.53 −0.64 −0.12 +1.79 warm superterran mesoplanet 619.4 Confirmed 2011
32 KOI-3282.01 0.71 0.04 −0.92 −0.12 +1.43 warm superterran mesoplanet 1162.9 Kepler candidate 2011
33 KOI-4450.01 0.71 0.00 −0.83 −0.13 +1.33 warm superterran mesoplanet 2553.4 Kepler candidate 2011
34 KOI-4054.01 0.70 0.00 −0.91 −0.12 +1.30 warm superterran mesoplanet 1770.4 Kepler candidate 2011
35 KOI-4087.01 0.70 0.00 +0.01 −0.15 +0.38 warm superterran psychroplanet 706.5 Kepler candidate 2011
36 KOI-4583.01 0.69 0.07 −0.23 −0.12 +2.03 warm superterran psychroplanet 3265.0 Kepler candidate 2011
37 Kepler-298d 0.68 0.00 −0.86 −0.11 +2.11 warm superterran mesoplanet 11.9 Confirmed 2012
38 KOI-4005.01 0.68 0.00 −0.99 −0.13 +1.18 warm superterran thermoplanet 1914.8 Kepler candidate 2011
39 Kapteyn b 0.67 0.00 +0.08 −0.15 +0.57 warm superterran psychroplanet 12.7 Confirmed 2014
40 Kepler-62f 0.67 0.00 +0.45 −0.16 +0.19 warm superterran psychroplanet 1199.7 Confirmed 2013
41 Kepler-186f 0.64 0.00 +0.48 −0.17 −0.26 warm terran psychroplanet 492 Confirmed 2014
42 Kepler-174d 0.61 0.00 +0.32 −0.13 +1.77 warm superterran psychroplanet 878.3 Confirmed 2011
43 Gliese 667 Ce 0.60 0.00 +0.51 −0.16 +0.23 warm superterran psychroplanet 23.6 dubious 2013
44 KOI-2770.01 0.60 0.00 +0.33 −0.13 +1.77 warm superterran psychroplanet 1470.4 Kepler candidate 2011
45 Gliese 682 c 0.59 0.00 +0.22 −0.14 +1.19 warm superterran psychroplanet 16.6 Unconfirmed 2014
46 KOI-4356.01 0.55 0.00 +0.77 −0.14 +1.22 warm superterran psychroplanet 1239.7 Kepler candidate 2011
47 Gliese 581 d 0.53 0.00 +0.78 −0.14 +0.94 warm superterran hypopsychroplanet 20.2 dubious 2007
@1N/A ~Venus 0.78 0.00 −0.93 −0.28 −0.70 warm terran hyperthermoplanet 0 non-exoplanet prehistoric
@2N/A ~Mars 0.64 0.00 +0.33 −0.13 −1.12 warm subterran hypopsychroplanet 0 non-exoplanet prehistoric
@3N/A ~Mercury 0.39 0.00 −1.46 −0.52 −1.37 hot mercurian non-habitable 0 non-exoplanet prehistoric

Previous candidates

HD 85512 b was initially found to be potentially habitable,[9][10] but updated models for the boundaries of the habitable zone placed the planet interior to the HZ,[11][12] and it is now considered non-habitable.[7] Kepler-69c has gone through a similar process; though initially believed to be potentially habitable,[13] it was quickly realized that the planet is more likely to be similar to Venus,[14] and is thus no longer considered habitable.[7]

Similarly, Tau Ceti f was initially considered potentially habitable,[15] 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.[7]

See also

References

  1. ^ "VPL Glossary". washington.edu. 
  2. ^ "The Goldilocks Zone".  
  3. ^ "Milky Way Teeming With Billions Of Earth-Size Planets".  
  4. ^ a b Overbye, Dennis (November 4, 2013). "Far-Off Planets Like the Earth Dot the Galaxy".  
  5. ^ a b Petigura, Eric A.; Howard, Andrew W.; Marcy, Geoffrey W. (October 31, 2013). "Prevalence of Earth-size planets orbiting Sun-like stars".  
  6. ^ Khan, Amina (November 4, 2013). "Milky Way may host billions of Earth-size planets".  
  7. ^ a b c d "PHL's Exoplanets Catalog - Planetary Habitability Laboratory @ UPR Arecibo". Retrieved Too many dates to list. 
  8. ^ http://phl.upr.edu/library/notes/thenewpotentialhabitableexoplanetscandidatesofnasakepler
  9. ^ Kaltenegger, L. et al. (2011). "A Habitable Planet around HD 85512?".  
  10. ^ http://phl.upr.edu/press-releases/fivepotentialhabitableexoplanetsnow
  11. ^ Kopparapu, Ravi kumar et al. (2013). "Habitable Zones Around Main-Sequence Stars: New Estimates".  
  12. ^ http://phl.upr.edu/press-releases/anewhabitablezone
  13. ^ Barclay, Thomas; et al. (2013). "A super-Earth-sized planet orbiting in or near the habitable zone around Sun-like star".  
  14. ^ Kane, Stephen R. et al. (2013). "A Potential Super-Venus in the Kepler-69 System".  
  15. ^ http://phl.upr.edu/press-releases/twonearbyhabitableworlds

External links

  • "The Habitable Exoplanets Catalog" (PHL/UPR Arecibo)
  • Habitable Exoplanets Catalogue ranks alien worlds on suitability for life
  • Definition of "goldilocks" connoting "moderate characteristics" and examples referring to planets dating to 1935
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