Gliese 832 c has a minimum mass of 5.4 and an estimated radius of 1.75 Earths, the latter based on the same density. Since the planet orbits near its host star which is a cold red dwarf (half the size and 3% the solar luminosity), it receives about the same stellar flux than Earth. At a distance of 0.162AU, c resides inside the habitable zone and has an equilibrium temperature of estimated -20°C, absence of an atmosphere provided. However, the planet has a relatively high eccentricity (0.18), taking it very near to the predicted inner edge of the habitable zone in that temperatures may vary between -40°C to +7°C when closest to the star. The planet is likely tidally locked and, if so, it has a hot and a cold hemisphere and a narrow habitable stripe at the terminator. A much larger area of the planet may be habitable if it has an atmosphere capable of heat transfer. A too thick atmosphere however could render the planet somewhat Venus-like. A year on Gliese 832 c is 35.68 days short. A second known planet, b, orbits at 3.4AU once in 9.4 years and has a mass of 0.65 Jupiters.
Image credit: NASA/JPL Caltech (modified)
Planet Designation | Title | Constellation | Distance | SMA | Period | Mass | Radius | Year | |
---|---|---|---|---|---|---|---|---|---|
1 | Proxima b | Nearest Known Exoplanet | Centaurus | 4.24ly | 0.04856AU | 11.1868d | 1.27⊕ | 2016 | |
2 | Barnard b | Second Closest Known Exoplanet | Ophiuchus | 5.9ly | AU | d | 3.23⊕ | ||
3 | Epsilon Eridani b | Asteroid Belts and Controversal Planets | Eridanus | 10.48ly | 3.53AU | 2671d | 245⊕ | 2000 | |
4 | Ross 128 b | Third Closest Known Exoplanet | Virgo | 11.03ly | 0.0496AU | 9.8658d | 1.35⊕ | 2017 | |
5 | Tau Ceti e | Planets Needing Confirmation | Cetus | 11.91ly | 0.538AU | 162.87d | 3.29⊕ | 2017 | |
6 | Luyten's Star b | Only 1.2 Light-Years Away from Procyon | Canis Minor | 12.2ly | 0.091101AU | 18.6498d | 2.89⊕ | 2017 | |
7 | Kapteyn's Star c | Oldest-known Cold Exoplanet | Pictor | 12.76ly | 0.311AU | 121.54d | 4.8⊕ | 2014 | |
8 | Wolf 1061 c | Temperate Super-Earth or Super-Mars | Ophiuchus | 14.04ly | 0.089AU | 17.8719d | 3.41⊕ | 2015 | |
9 | Gliese 832 c | Large Planet as Temperate as Earth | Grus | 16.1ly | AU | d | 5.4⊕ | ||
10 | 40 Eridani b | Hot Super-Earth in Triple Star System | Eridanus | 16.26ly | 0AU | 42.378d | 8.47⊕ | 2018 | |
11 | Gliese 3323 b | Little Known in Habitable Zone | Eridanus | 17.54ly | 0.03282AU | 5.3636d | 2.02⊕ | 2017 | |
12 | LTT 1445A b | Planet in Triple Red Dwarf System | Eridanus | 22.5ly | 0.022AU | 5.35876d | 2.2⊕ | 1.18⊕ | 2019 |
13 | Gliese 667C c | Earth-like Planet in Triple Star System | Scorpius | 23.6ly | 0.125AU | 28.14d | 3.71⊕ | 2013 | |
14 | HD 85512 b | Bordering the Habitable Zone | Vela | 36.4ly | 0.26AU | 58.43d | 3.6⊕ | 2011 | |
15 | Gliese 1132 b | Heat Planet with Atmosphere | Vela | 39.3ly | 0.0153AU | 1.62893d | 1.66⊕ | 1.13⊕ | 2015 |
16 | Trappist-1 d | Small but Most Earth-like Known Planet | Aquarius | 39.5ly | 0.02227AU | 4.04922d | 0.297⊕ | 0.78⊕ | 2016 |
17 | LHS 1140 b | A Massive Super-Earth Inside Habitable Zone | Cetus | 40.67ly | 0.0946AU | 24.7372d | 6.64⊕ | 1.72⊕ | 2017 |
18 | Gliese 143 b | A Huge Neptunian Around a K-Star | Reticulum | 53.2ly | 0.1915AU | 35.6125d | 30.63⊕ | 2.61⊕ | 2019 |
19 | TOI-270 b | Nearby M-Dwarf Planets | Dorado | 73.23ly | AU | d | 1.9⊕ | ||
20 | Gliese 3470 b | Evaporating Planet | Cancer | 95.5ly | 0.0355AU | 3.33665d | 13.4⊕ | 4.57⊕ | 2012 |
21 | K2-3 b | Super-Earths Trio in Leo | Leo | 143.9ly | 0.0747AU | 10.0547d | 2.7⊕ | 2.07⊕ | 2015 |
22 | HIP 11915 b | A Twin of Jupiter | Cetus | 175ly | AU | d | 0.99⊕ | ||
23 | K2-288B b | Detected by Citizen Scientists | Taurus | 226ly | 0.164AU | 31.3935d | 4⊕ | 1.90⊕ | 2018 |
24 | Kepler-186 f | Earth-sized Cold Kepler Planet | Cygnus | 582ly | 0.432AU | 129.944d | 1.4⊕ | 1.16⊕ | 2014 |
Most of the stars introduced on this page are 'Red Dwarfs'. Actually they represent the most common type of stars. About 73% of all stars in the Milky Way galaxy are dim red dwarfs, featuring less than half the solar surface temperature and low luminosity, but in turn high stellar activity, such as flares and hazardous radiation that can hit red dwarf planets hard potentially prohibiting formation of known lifeforms.
Given its minute energy emission, the habitable zone (HBZ, an imaginary ring where temperatures support liquid water) of a red dwarf is situated near the star, as are planets orbiting inside this zone. The gravitational pull of the star can tidally lock a nearby planet which then faces one hemisphere to the star while the other is enshrouded in darkness - like the Earth moon - the axial rotation period equals the orbital period.
Some densely populated systems, such as TRAPPIST-1, have several planets orbiting in close proximity in that an observer on a planet could see other planets larger than our moon in the sky. Also, the planet may have one or multiple moons themselves. In any case a truly impressive spectacle with fast changes.
Due to their low visual luminosity no known red dwarf is visible by the naked eye, not even the nearest such as Proxima Centauri or the solitary Barnard's Star. Others, such as Gliese 667, are triple star systems but anywhere near visual magnitude
Image Credit: NASA/ESA/STScl