LHS 1140 b

LHS 1140 b orbits a small red dwarf, LHS 1140. It is 18.4% the mass and 21.6% the radius of the Sun with a spectral type of M4.5V. The temperature of LHS 1140 is , and it has a luminosity of 0.0038 times that of the Sun. It is at least 5 billion years old. For comparison, the Sun is 1 solar mass and radius, has a temperature of with 1 solar luminosity, is 4.5 billion years old, and has the spectral type of G2V. In addition, LHS 1140 is a very inactive star, with no major flare events found by the discovery team of its planet. Unlike most stars its size, LHS 1140 has low amounts of activity and rotates every 130 days. ==Characteristics==

Mass and radius LHS 1140 b has been detected using both the radial velocity method (which measures the mass of a companion object) and transit photometry (which determines radius). Because of this, LHS 1140 b is one of very few potentially habitable exoplanets with a determined mass and radius, the others all being those around TRAPPIST-1. The planet's radius is well-constrained at , equivalent to about 11,000 km. == Habitability ==

LHS 1140 b orbits close to the outer edge of the habitable zone, a region around a star where temperatures are just right for liquid water to pool on the surface of orbiting planets, given sufficient atmospheric pressure. The equilibrium temperature of LHS 1140 b is rather low, at , as cold as the polar regions on Earth. However, this is the calculated temperature excluding the impact of a thick atmosphere. With an Earth-like greenhouse effect, the surface temperature is about , but since the planet is so massive, the greenhouse effect may be even higher. At twice the greenhouse effect of Earth, LHS 1140 b would have a comfortable surface temperature of . In addition, the host star is so inactive that atmospheric erosion will not be very high, suggesting the planet should be able to retain its atmosphere over long timescales. In this case, it could receive enough radiogenic heating and tidal heating for significant amounts of liquid water to be transported through the ice shell to its surface via cryovolcanic venting of water-rich geysers. ==See also==