While we know that yellow dwarf stars like our sun are capable of supporting life, there’s another star type that is a prime hunting ground for potentially habitable exoplanets.
M-dwarf stars are extremely common in the Universe and a typical one is relatively small and dim, making it easy for astronomers to detect a passing planet. If orbiting planets huddle close enough to an M-dwarf, in theory they could fall within the habitable zone where surface liquid water, and thus life, is possible.
Yet, an M-dwarf’s habitable zone is poorly understood. It is not clear how far away the planets need to be orbiting from the star for surface liquid water to be possible. Because planets in this range orbit so close to an M-dwarf they may be tidally locked, said Ravi Kumar Kopparapu, an assistant research scientist at the NASA Goddard Space Flight Center in Maryland.
“They’re always facing the same side of the star, just like the Moon does around the Earth,” he said.
This position could potentially stabilize the climate for life, but on the other hand, the side facing the star might be very hot while the side facing away is very cold.
Kopparapu said a better understanding of habitable zones around M-dwarfs needs to come quickly because of upcoming missions in exoplanet research. NASA’s Transiting Exoplanet Survey Satellite (TESS) is scheduled to launch next year to observe more planets and to serve as a guidepost for NASA’s James Webb Space Telescope in 2018. James Webb can provide higher resolution data that can tell us about what kind of gases are present in the atmosphere of a planet orbiting an M-dwarf star. This data can bring out details such as a planet’s temperature, revealing the potential for the right conditions to exist for life.
A paper based on Kopparapu’s research, “The inner edge of the habitable zone for synchronously rotating planets around low-mass stars using general circulation models,” was recently published in The Astrophysical Journal.