New exoplanet appears ripe for atmosphere observations

Astronomers have discovered a new exoplanet about 25 light-years away, and they say it should be the first target when the next-generation James Webb Space Telescope launches later this year (Science 2021, DOI: 10.1126/science.abd7645). Trifon Trifonov of the Max Planck Institute for Astronomy and colleagues found the exoplanet, Gliese 486 b, during a survey of about 350 red dwarf stars. They predict it is rocky, a little larger than Earth, and about as hot as Venus. Their observations also suggest that Gliese 486 b has a metal core, like Earth, but that it is tidally locked to its star, Gliese 486, similar to the way the moon is locked to Earth. It orbits Gliese 486 once every day and a half. Gliese 486 b is attractive for telescope observations; because it’s so close to Gliese 486, a bright star, it should offer astronomers good transit spectroscopy, which relies on the star’s light passing through the exoplanet’s atmosphere. Gliese 486 b is hot enough that scientists will also be able to do emission spectroscopy based on radiation from the exoplanet itself. Trifonov says that compared with other rocky exoplanets, Gliese 486 b appears to have the best characteristics for emission spectroscopy and the second-best for transit spectroscopy. But that all depends on Gliese 486 b’s having an atmosphere; Trifonov says his team’s models put the exoplanet on a knife’s edge, with enough gravity to retain an atmosphere but enough stellar radiation to blow it away.