LHS 1140 b
A Massive Super-Earth Inside Habitable Zone
LHS 1140, or Gliese 3053, is an over 5 billion years old inactive red dwarf star with 15% of the mass and 19% of the radius of the Sun. It hosts two known planets plus another unconfirmed candidate. Planet b has about 6.7 times the mass of Earth and orbits close to the outer edge of the habitable zone at a distance to the star of 0.0875AU with an orbital period of 24.74 days. Measuring 1.28 Earth radii, the planet transits the star on the line of sight from Earth. Given its mass and radius, b has a high density of around 12.5 g/cm³, hence a surface gravity about 3.25 that of Earth resulting in an escape velocity of 24km/s. It is of rocky, iron-rich composition, while its iron-nickle core may take up to 75% of the planet's total mass beating Earth's core four times. At its distance to the star the planet receives merely 41% the stellar flux of Earth while its high orbit eccentricity of 0.3 causes significant temperature variations over its year. Assuming absence of a thick atmosphere and greenhouse effects, the equilibrium temperature of LHS 1140 b is estimated −43°C, as cold as Earth's polar regions. If it has some kind of heat collector, which cannot entirely be ruled out because of its high mass, the temperature could as well be comfortable 25°C.
Image credit: ESO/spaceengine.orgPosted on: 2018-12-08
Overview
| 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 | 0.02294AU | 3.1533d | 3.23⊕ | 2024 | |
| 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 | Planet 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 3323 b | Little Known in Habitable Zone | Eridanus | 17.54ly | 0.03282AU | 5.3636d | 2.02⊕ | 2017 | |
| 10 | LTT 1445A b | Planet in Triple Red Dwarf System | Eridanus | 22.5ly | 0.022AU | 5.35876d | 2.2⊕ | 1.18⊕ | 2019 |
| 11 | Gliese 667C c | Earth-like Planet in Triple Star System | Scorpius | 23.6ly | 0.125AU | 28.14d | 3.71⊕ | 2013 | |
| 12 | Gliese 1132 b | Heat Planet with Atmosphere | Vela | 39.3ly | 0.0157AU | 1.62893d | 1.66⊕ | 1.19⊕ | 2015 |
| 13 | Trappist-1 d | Small but Most Earth-like Known Planet | Aquarius | 39.5ly | 0.02227AU | 4.04922d | 0.297⊕ | 0.78⊕ | 2016 |
| 14 | LHS 1140 b | A Massive Super-Earth Inside Habitable Zone | Cetus | 40.67ly | 0.0946AU | 24.7372d | 6.64⊕ | 1.72⊕ | 2017 |
| 15 | Gliese 143 b | A Huge Neptunian Around a K-Star | Reticulum | 53.2ly | 0.1915AU | 35.6125d | 30.63⊕ | 2.61⊕ | 2019 |
| 16 | TOI-270 b | Nearby M-Dwarf Planets | Dorado | 73.23ly | 0.03197AU | 3.36015d | 1.9⊕ | 1.21⊕ | 2019 |
| 17 | Gliese 3470 b | Evaporating Planet | Cancer | 95.5ly | 0.0355AU | 3.33665d | 13.4⊕ | 4.57⊕ | 2012 |
| 18 | K2-3 b | Super-Earths Trio in Leo | Leo | 143.9ly | 0.0747AU | 10.0547d | 2.7⊕ | 2.07⊕ | 2015 |
| 19 | K2-288B b | Detected by Citizen Scientists | Taurus | 226ly | 0.164AU | 31.3935d | 4⊕ | 1.90⊕ | 2018 |
| 20 | Kepler-186 f | Earth-sized Cold Kepler Planet | Cygnus | 582ly | 0.432AU | 129.944d | 1.4⊕ | 1.16⊕ | 2014 |
Red Dwarfs in a Nutshell
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.
Likelihood of life low because:
- Low stellar energy flux
- Tidal lock, tidal heating
- Narrow habitable zone
- Stellar variations, flares, stellar 'wind' of charged particles
On the other hand, if conditions are favorable:
- A red dwarf is aged, known for longevity while some are rather inactive.
- The lower the mass of a red dwarf the longer it will 'live', potentially trillions of years.
- A planet mass big enough to hold an atmosphere capable of heat transfer.
- A low orbit eccentricity for stable meteorological conditions.
- Planets at the outer edge of the HBZ can retain water.
- Planet may have a solid core and a magnetic field shield.
- Lots of known lifeforms on Earth developed and are living under brutal conditions.
Observation
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
