A pair of planets orbiting a nearby star called Teegarden’s star may be just right for liquid water, and perhaps even life. The planets, discovered in June 2019, could support water on their surfaces if they have very thin atmospheres or relatively thick ones.
Teegarden’s star – named after Bonnard Teegarden, the leader of the team that discovered it – is about 12.5 light years away, and it has two planets called Teegarden’s star b and c. It is a small and dim star, and its planets have tight and fast orbits, circling it about every 5 and 11 days, respectively. They are both slightly more massive than Earth.
Because the planets are so close to their star, they are likely tidally locked, meaning that the same side of the planet is facing the sun at all times. If they don’t have atmospheres, each planet would have a hot side and a cold side, but if they do then winds could transport heat around the globe.
Advertisement
Amri Wandel at the Hebrew University of Jerusalem and Lev Tal-Or at Tel Aviv University calculated what sort of atmosphere would be required for Teegarden’s planets to maintain liquid oceans on their surfaces. They found that if the atmosphere is between a third as dense as Earth’s and seventeen times as dense, there is likely some region on at least one of the planets that could have water.
It may actually make it more likely that liquid water and life can exist on a planet if it is tidally locked, says Wandel. Temperatures do vary from equator to poles on Earth, but over a relatively short range. On a tidally locked planet, temperatures can vary to a greater degree from region to region. “This gives a wider range of possible atmospheres that allow for life,” says Wandel.
There are some potential issues with finding life on a tidally locked world, says Jessie Christiansen at the NASA Exoplanet Science Institute at the California Institute of Technology, including that some astrobiologists believe that a day-night cycle is important for life. Also, tidal locking may suppress the planets’ magnetic fields, which would make them more susceptible to harmful charged particles from their star.
Nevertheless, “the two planets orbiting Teegarden’s star are incredibly tantalising,” she says. “These new planets will remain under scrutiny for some time while we explore these possibilities.”
The Astrophysical Journal Letters
