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A Nearby System with two Potentially Habitable Worlds


Zechmeister et al. (2019) report as part of the CARMENES project the discovery of two potentially habitable planets around Teegarden's Staran old nearby red dwarf star 12 light-years away in the Aries constellation. Both planets have minimum masses similar to Earth and orbit within the star's habitable zone (1).

Teegarden's Star is the 24th nearest star system to our own Solar System and the nearest fourth with potentially habitable planets, after Proxima Centauri, Tau Ceti, and Luyten's Star. It is also the closest with multiple small planets in the habitable zone, with similar insolations as our Earth and Mars.

The innermost planet Teegarden b has a 60% chance of having a temperate surface environment, that is temperatures between 0° to 50°C. Surface temperature should be closer to 28°C (2) assuming a similar terrestrial atmosphere but could be higher or lower depending on its composition.

Teegarden b is the planet with the highest Earth Similarity Index (ESI) discovered so far, which means that it has the closest mass and insolation to terrestrial values, albeit we only know its minimum mass (3). However, how this translates to habitability depends on many other factors, especially since this planet orbits a red dwarf star.

Red dwarf star are known to emit strong flares that might erode the atmospheres of planets during their lifetime. Teegarden b should be tidally locked and could even be devoid of an atmosphere or water depending on its thermal evolution.

The outermost planet Teegarden c only has a 3% chance of having a temperate surface environment. Surface temperature should be close to -47°C (2) assuming a terrestrial atmosphere, similar to the temperatures of Mars.

Teegarden's Star is observable from the Arecibo Observatory. Its proximity makes it an excellent candidate for studies of the activity and plasma environment around this star in the radio spectrum, which might provide more information about the past and current space environment experienced by its planets.

Both planets were added to the Habitable Exoplanets Catalog together with K2-296 b, one of 18 planets recently discovered by the K2 mission. Teegarden b and c are part of the top 19 know planets that might support habitable environmentsThe catalog lists up to 52 potentially habitable planets out of nearly 4000 known planets.

Notes:

(1) The habitable zone as defined by Kopparapu et al. (2014).
(2) For Teegarden b Tsurf = 28 ± 45 °C and for Teegarden c Tsurf = -47 ± 34 °C (90% confidence level). Both temperature estimates are assuming an Earth-like atmosphere around a M-dwarf (Méndez & Rivera-Valentín, 2017; and Méndez et al., 2019 in preparation).
(3) The Earth Similarity Index (ESI) as defined by Dirk Schulze-Makuch et al. (2011) and explained here.

Additional Links

Figures



Fig. #1. Top 19 potentially habitable exoplanets, sorted by distance from Earth.



Fig. #2. Top 19 potentially habitable exoplanets, sorted by similar size and insolation to Earth.



FIg. #3. The planetary system around Teegarden’s Star.



Fig. #4. Planets in the habitable zone.


Fig. #5. Map with the stars with potentially habitable exoplanets.


Table #1. Top potentially habitable planets listed in the Habitable Exoplanets Catalog, sorted by the Earth Similarity Index (ESI). These are small planets with a radius less than 1.5 Earth radii or minimum mass less than 5 Earth masses, orbiting within the habitable zone of their star. They are more likely to be rocky but this is more uncertain for planets with only known minimum mass.

NameTypeMass
(ME)
Radius
(RE)
Flux
(SE)
Teq
(K)
Period
(days)
Distance
(ly)
ESI
001. Teegarden b (N)M-Warm Terran≥1.051.152644.9120.95
002. K2-72 eM-Warm Terran1.291.1126124.22170.90
003. GJ 3323 bM-Warm Terran≥2.021.232655.4170.90
004. TRAPPIST-1 dM-Warm Subterran0.410.771.212674.0390.89
005. TRAPPIST-1 eM-Warm Terran0.620.920.702336.1390.87
006. GJ 667 C fM-Warm Terran≥2.540.8524539.0220.87
007. Proxima Cen bM-Warm Terran≥1.270.6922711.24.20.87
008. Kepler-442 bK-Warm Terran1.350.72235112.311150.85
009. GJ 273 bM-Warm Terran≥2.891.1926618.6120.84
010. Wolf 1061 cM-Warm Terran≥3.411.3627517.9140.79
011. GJ 667 C cM-Warm Terran≥3.811.3327428.1220.78
012. tau Cet eG-Warm Terran≥3.931.61285162.9120.74
013. Kepler-1229 bM-Warm Terran1.400.4921386.87690.73
014. GJ 667 C eM-Warm Terran≥2.540.4621062.2220.71
015. TRAPPIST-1 fM-Warm Terran0.681.040.402039.2390.70
016. Kepler-62 fK-Warm Terran1.410.42205267.312000.69
017. Teegarden c (N)M-Warm Terran≥1.110.3719911.4120.68
018. TRAPPIST-1 gM-Warm Terran1.341.130.2718412.4390.59
019. Kepler-186 fM-Warm Terran1.170.26182129.95610.58

Table #2. An additional sample of potentially habitable planets listed in the Habitable Exoplanets Catalog, sorted by the Earth Similarity Index (ESI). These are bigger planets with a radius between 1.5 to 2.5 Earth radii or minimum mass between 5 and 10 Earth masses orbiting within the habitable zone of their star. There are less likely to be rocky and the bigger ones could be water worlds or mini-Neptunes instead.

NameTypeMass
(ME)
Radius
(RE)
Flux
(SE)
Teq
(K)
Period
(days)
Distance
(ly)
ESI
001. Kepler-452 bG-Warm Superterran1.631.11261384.817860.83
002. Kepler-62 eK-Warm Superterran1.611.18266122.412000.82
003. Kepler-1652 bM-Warm Superterran1.600.8324338.18220.82
004. Kepler-1544 bK-Warm Superterran1.780.90248168.811380.80
005. K2-3 dM-Warm Superterran1.511.5028244.61440.80
006. Kepler-296 eM-Warm Superterran1.521.5027634.17370.80
007. Kepler-283 cK-Warm Superterran1.820.9024892.714770.79
008. Kepler-1410 bK-Warm Superterran1.781.3427460.911960.78
009. Kepler-1638 bG-Warm Superterran1.871.39276259.328660.76
010. K2-296 b (N)M-Warm Superterran1.871.4027728.25220.76
011. Kepler-296 fM-Warm Superterran1.800.6622563.37370.75
012. Kepler-705 bM-Warm Superterran2.110.8324356.18180.74
013. Kepler-440 bK-Warm Superterran1.911.49275101.18510.74
014. Kepler-1653 bK-Warm Superterran2.171.03257140.324610.74
015. GJ 832 cM-Warm Superterran≥5.401.2226635.7160.73
016. Kepler-1606 bG-Warm Superterran2.071.41277196.428690.73
017. Kepler-1090 bG-Warm Superterran2.251.20267198.722890.72
018. Kepler-61 bK-Warm Superterran2.151.3927359.910240.72
019. Kepler-443 bK-Warm Superterran2.350.92249177.725400.71
020. K2-18 bM-Warm Superterran8.922.371.0825732.91110.71
021. Kepler-22 bG-Warm Superterran2.381.11261289.96190.71
022. K2-9 bM-Warm Superterran2.251.3727618.42710.71
023. Kepler-26 eM-Warm Superterran2.411.1326346.811050.70
024. Kepler-1552 bK-Warm Superterran2.471.10261184.820150.70
025. Kepler-1540 bK-Warm Superterran2.490.92250125.48540.70
026. LHS 1140 bM-Warm Superterran6.981.730.4821224.7410.69
027. Kepler-1632 bF-Warm Superterran2.471.27270448.319040.69
028. HD 40307 gK-Warm Superterran≥7.091.12258197.8420.69
029. GJ 163 cM-Warm Superterran≥6.801.2526925.6490.69
030. Kepler-298 dK-Warm Superterran2.501.2927177.516430.68
031. K2-288 B bM-Warm Superterran1.910.4320631.42140.64
032. GJ 3293 dM-Warm Superterran≥7.600.5521948.1660.62
033. Kepler-174 dK-Warm Superterran2.190.43206247.412090.61