List of potentially habitable exoplanets
This is a list of potentially habitable exoplanets and possible exoplanets 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 the University of Puerto Rico at Arecibo.
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.
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, 11 billion of which may be orbiting Sun-like stars.
A review in 2015 came to the conclusion that the exoplanets Kepler-62f, Kepler-186f and Kepler-442b were likely the best candidates for being potentially habitable. These are at a distance of 1200, 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.
|Notable exoplanets – Kepler Space Telescope|
(Kepler-62e, Kepler-62f, Kepler-186f, Kepler-296e, Kepler-296f, Kepler-438b, Kepler-440b, Kepler-442b)
(Kepler Space Telescope; 6 January 2015).
|Notable exoplanets – Kepler Space Telescope|
List from the Habitable Exoplanets Catalog
The data in the following table is from the Habitable Exoplanets Catalog. 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.
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. Note that even though many planets have an HZD value similar to Venus (−0.93), including Kepler-438b, the HZD is not used to rule on whether a planet has suffered a runaway greenhouse effect or not, and therefore, Kepler-438b is currently assumed to be a mesoplanet rather than a hyperthermoplanet.
- 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.
|This section does not cite any references or sources. (August 2015)|
(For comparison purposes, the four solar terrestrial planets are included in this list)
|Name||ESI||SPH||HZD||HZC||HZA||pClass||Star||hClass||Distance (ly)||Status||Year of
|Earth||1.00||0.72||−0.50||−0.31||−0.52||warm terran||G||mesoplanet||0||Non-exoplanet, inhabited||prehistoric|
|Gliese 667 Cc||0.84||0.64||−0.62||−0.15||+0.21||warm terran||M||mesoplanet||23.6||confirmed||2011|||
|KOI-3010.01||0.84||0.63||−0.88||−0.16||−0.06||warm superterran||K||mesoplanet||1213.4||Kepler candidate||2011|||
|Gliese 832 c||0.81||0.96||−0.72||−0.15||+0.43||warm superterran||M||mesoplanet||16.1||confirmed||2014|
|KOI-2418.01||0.79||0.00||−0.40||−0.15||+0.44||warm superterran||M||psychroplanet||996.9||Kepler candidate||2011|
|Tau Ceti e||0.78||0.00||−0.92||−0.15||+0.16||warm superterran||G||mesoplanet||11.9||unconfirmed||2012|
|Gliese 180 c||0.77||0.42||−0.53||−0.14||+0.64||warm superterran||M||mesoplanet||39.5||unconfirmed||2014|
|Gliese 667 Cf||0.77||0.00||-0.22||−0.16||+0.08||warm terran||M||psychroplanet||23.6||dubious||2013|
|Gliese 581 g||0.76||1.00||-0.70||−0.15||+0.28||warm superterran||M||mesoplanet||20.2||dubious||2010|
|KOI-2474.01||0.76||0.00||−0.93||−0.15||+0.25||warm superterran||G||mesoplanet||1605.7||Kepler candidate||2011|
|KOI-2469.01||0.76||0.71||−0.75||−0.13||+0.99||warm superterran||K||mesoplanet||1556.8||Kepler candidate||2011|
|KOI-2992.01||0.76||0.52||−0.54||−0.13||+1.06||warm superterran||K||mesoplanet||1375.4||Kepler candidate||2011|
|KOI-4333.01||0.75||0.00||−0.90||−0.15||+0.32||warm superterran||F||thermoplanet||2504.7||Kepler candidate||2011|
|Gliese 163 c||0.75||0.02||−0.96||−0.14||+0.58||warm superterran||M||mesoplanet||48.9||confirmed||2012|
|Gliese 180 b||0.75||0.41||−0.88||−0.14||+0.74||warm superterran||M||mesoplanet||39.5||unconfirmed||2014|
|HD 40307 g||0.74||0.04||−0.23||−0.14||+0.77||warm superterran||K||psychroplanet||41.7||confirmed||2012|
|KOI-854.01||0.74||1.00||−0.72||−0.13||+1.39||warm superterran||M||mesoplanet||1077.7||Kepler candidate||2011|
|KOI-4550.01||0.74||1.00||−0.82||−0.13||+0.97||warm superterran||K||mesoplanet||1847.5||Kepler candidate||2011|
|KOI-2762.01||0.73||0.10||−0.27||−0.14||+1.01||warm superterran||K||mesoplanet||1169.5||Kepler candidate||2011|
|KOI-1871.01||0.72||0.27||−0.88||−0.12||+1.34||warm superterran||K||mesoplanet||1176.7||Kepler candidate||2011|
|KOI-4036.01||0.72||0.99||−0.77||−0.12||+1.49||warm superterran||K||mesoplanet||1135.0||Kepler candidate||2011|
|Gliese 422 b||0.71||0.17||−0.41||−0.13||+1.11||warm megaterran||M||mesoplanet||41.3||unconfirmed||2014|
|KOI-3282.01||0.71||0.04||−0.92||−0.12||+1.43||warm superterran||M||mesoplanet||1162.9||Kepler candidate||2011|
|KOI-4450.01||0.71||0.00||−0.83||−0.13||+1.33||warm superterran||G||mesoplanet||2553.4||Kepler candidate||2011|
|KOI-4054.01||0.70||0.00||−0.91||−0.12||+1.30||warm superterran||G||mesoplanet||1770.4||Kepler candidate||2011|
|KOI-4583.01||0.69||0.07||−0.23||−0.12||+2.03||warm superterran||G||psychroplanet||3265.0||Kepler candidate||2011|
|Kapteyn b||0.67||0.00||+0.08||−0.15||+0.57||warm superterran||M||psychroplanet||12.7||confirmed||2014|
|KOI-2770.01||0.60||0.00||+0.33||−0.13||+1.77||warm superterran||K||psychroplanet||1470.4||Kepler candidate||2011|
|Gliese 667 Ce||0.60||0.00||+0.51||−0.16||+0.23||warm terran||M||psychroplanet||23.6||dubious||2013|
|Gliese 682 c||0.59||0.00||+0.22||−0.14||+1.19||warm superterran||M||psychroplanet||16.6||unconfirmed||2014|
|KOI-4356.01||0.55||0.00||+0.77||−0.14||+1.22||warm superterran||K||psychroplanet||1239.7||Kepler candidate||2011|
|Gliese 581 d||0.53||0.00||+0.78||−0.14||+0.94||warm superterran||M||hypopsychroplanet||20.2||unconfirmed||2007|||
|~Venus||0.78||0.00||−0.93||−0.28||−0.70||warm terran||G||hyperthermoplanet||close to zero||non-exoplanet||prehistoric|
|~Mars||0.64||0.00||+0.33||−0.13||−1.12||warm subterran||G||hypopsychroplanet||close to zero||non-exoplanet||prehistoric|
|~Mercury||0.39||0.00||−1.46||−0.52||−1.37||hot mercurian||G||non-habitable||close to zero||non-exoplanet||prehistoric|
HD 85512 b was initially found to be potentially habitable, but updated models for the boundaries of the habitable zone placed the planet interior to the HZ, and it is now considered non-habitable. Kepler-69c has gone through a similar process; though initially believed to be potentially habitable, it was quickly realized that the planet is more likely to be similar to Venus, and is thus no longer considered habitable.
Similarly, Tau Ceti f was initially considered potentially habitable, 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.
KOI-1686.01 was also considered even the single-most potentially habitable exoplanet after its discovery in 2011, until it was proved a false positive by NASA in 2015.
- Carbon planet
- Earth analog
- Extraterrestrial life
- Extraterrestrial liquid water
- Goldilocks principle
- Habitability of red dwarf systems
- Habitable zone
- Hypothetical types of biochemistry
- List of multiplanetary systems
- List of nearby stars
- List of nearest terrestrial exoplanet candidates
- List of Potentially Habitable Exoplanets Kepler Candidates
- Natural satellite habitability
- List of potentially habitable moons
- Planetary habitability
- Rare Earth hypothesis
- Terrestrial planet
- Superhabitable Exoplanet
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- Habitable Exoplanets Catalogue ranks alien worlds on suitability for life
- Definition of "goldilocks" connoting "moderate characteristics" and examples referring to planets dating to 1935