Habitability and sub glacial liquid water on planets of M-dwarf stars

Abstract

A long-standing issue in astrobiology is whether planets orbiting the most abundant type of stars, M-dwarfs, can support liquid water and eventually life. A new study shows that subglacial melting may provide an answer, significantly extending the habitability region, in particular around M-dwarf stars, which are also the most promising for biosignature detection with the present and near-future technology.

Extended Habitability of Exoplanets Due to Subglacial Water

“…The extended habitability region described above, in particular around the abundant M dwarfs, may significantly enhance the number of biotic planets. Wandel (2023) estimated that considering planets of M dwarfs and an extended HZ may increase the abundance of potentially habitable worlds by a factor of up to ∼100, compared to only G-type stars with a conservative HZ. This estimate is based on the known relative abundances of M-, K-, and G-type stars and the Kepler statistics of Earth-size planets in the HZ depending on the star type (Bryson et al 2020), combined with the enhancement of the HZ.…”

“…Hence compared to a conservative HZ the extended HZ would enhance the number of potentially habitable planets by at least another factor of 5, which together with the above factor of 20 due to stellar population gives a factor of 100. Figure 2 of Wandel (2023) shows the number of expected habitable planets as a function of the distance from Earth for various star types and HZ models. For example, within 30 pc from Earth about 100 habitable planets are expected with the most conservative assumptions (only G-type stars and a conservative HZ), while for the most optimistic assumptions (including M-type stars and an extended HZ) their number could be as high as 10,000.…”

“…They modeled the evolution of ice sheets and the conditions that allow liquid water to be produced and maintained at temperatures above freezing on Earth-like exoplanets. Applying their results Wandel (2023) enhanced the definition of habitability by including subglacial liquid water, suggesting a more extended circumstellar habitable region with a potential for liquid water. In colder planets, outside the traditional HZ geothermal heat may suffice to maintain basal melting.…”

“…In this work we extend the model of Wandel (2023) and apply it to recent observations, obtaining two important new results: (i) the detection of water vapor in GJ 486 b is used as empirical support for the capability of closely orbiting rocky planets of M stars to maintain or renew water and atmosphere, contrary to previous suggestions that stellar activity during the early evolutionary stage of M dwarfs erode the atmosphere and destroy eventual water on such planets (Section 4); and (ii) the extended HZ boundaries due to subglacial water are combined with the analytical climate model of Wandel (2018) to demonstrate that habitable surface temperatures are consistent with a fairly wide range of atmospheric properties for several representative well-known HZ Earth-and super-Earth-sized planets of M stars (Section 6).…”