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 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)	ESI	Refs/Notes
Earth	Sun (Sol)	G2V	1.00	1.00	1.00	255	365.24	—	1.00	[14]
Teegarden's Star b	Teegarden's Star	M7V	≥1.05	—	1.15	264	4.91	12.58	0.95	[15]
TOI 700 d	TOI 700	M2V	~1.72	1.14	0.87	246	37.4	101	0.93
K2-72e	K2-72	M?V	~2.21	1.29	1.11	261	24.2	217	0.90	[16]
TRAPPIST-1d	TRAPPIST-1	M8V	0.30	0.78	1.04	258	4.05	39	0.91	Confirmed to be rocky[17][18]
Kepler-1649c	Kepler-1649	M5V	—	1.06	0.75	237	19.5	301	0.90	[19]
Proxima Centauri b	Proxima Centauri	M5V	≥1.27	—	0.70	228	11.186	4.25	0.87	[20]
Gliese 1061 d	Gliese 1061	M5V	≥1.64	—	0.69	218	13.0	12	0.86
Gliese 1061 c	Gliese 1061	M5V	≥1.74	—	1.45	275	6.7	12	0.86
Ross 128 b	Ross 128	M4V	≥1.40	—	1.48	280	9.87	11.03	0.86	[21]
Luyten b	Luyten's Star	M3V	≥2.89	—	1.06	258	18.65	12.36	0.91	[22]
TRAPPIST-1e	TRAPPIST-1	M8V	0.77	0.91	0.67	230	6.1	39	0.95	Confirmed to be rocky[17][18]
Kepler-442b	Kepler-442	K?V	—	1.35	0.70	233	112.3	1193	0.84	[1]
Wolf 1061c	Wolf 1061	M3V	≥3.41	—	1.30	271	17.9	13.8	0.76	[1]
Gliese 667 Cc	Gliese 667 C	M1V	≥3.81	—	0.88	247	28.1	23.62	0.85	[23][1]
Kepler-1229b	Kepler-1229	M?V	—	1.40	0.49	213	86.8	865	0.73	[1]
TRAPPIST-1f	TRAPPIST-1	M8V	0.93	1.05	0.38	200	9.2	39	0.70	Confirmed to be rocky[17][18]
Kepler-62f	Kepler-62	K2V	—	1.41	0.41	204	267.3	981	0.69	[1][24]
Teegarden's Star c	Teegarden's Star	M7V	≥1.11	—	0.37	199	11.4	12.58	0.68	[15]
Kepler-186f	Kepler-186	M1V	—	1.17	0.29	188	129.9	579	0.64	[1]
Tau Ceti f	Tau Ceti	G8V	≥3.93	—	0.32	190	636.1	12	0.58	[1]
TRAPPIST-1g	TRAPPIST-1	M8V	1.15	1.15	0.26	182	12.4	39	0.59	Confirmed to be rocky[17][18]
Kapteyn b*	Kapteyn's Star	M1VI	≥4.8	—	0.43	205	48.6	13	0.67	Controversial[25]
Kepler-452b*	Kepler-452	G2V	—	1.63	1.11	261	384.8	1799	0.83	Not confirmed[1][26][27]
Kepler-62e	Kepler-62	K2V	—	1.61	1.15	264	122.4	981	0.83	[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	0.85	[1][29]
Kepler-283c	Kepler-283	K5V	—	1.82	0.90	248	92.7	1526	0.79	[1]
K2-296b	K2-296	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	0.60	[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	0.81	[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	0.73	[1][33]
Kepler-443b	Kepler-443	K3V	—	2.35	0.89	247	177.7	2615	0.71	[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	0.74	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	0.61	[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

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

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

• Carbon planet
• Earth analog
• Extraterrestrial life
• Extraterrestrial liquid water
• Goldilocks principle
• Habitability of red dwarf systems
• Habitable zone
• Hypothetical types of biochemistry
• List of exoplanets
• Earth Similarity Index
• List of multiplanetary systems
• List of nearby stars
• List of nearest terrestrial exoplanet candidates
• List of Kepler exoplanet candidates in the habitable zone
• Natural satellite habitability
• List of potentially habitable moons
• Ocean planet
• Planetary habitability
• Rare Earth hypothesis
• Super-Earth
• Superhabitable planet
• Terrestrial planet
• Timeline of astronomical maps, catalogs, and surveys

Notes

References

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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