The star TRAPPIST-1, first discovered in 1999, is an ultracool red dwarf (or M dwarf). These are the most common type of star in the Milky Way, and, presumably, the universe. Due to their diminutive size, such stars put out much less energy than stars like the Sun. But red dwarfs are also known to sport strong stellar winds and violent flares, which has raised questions about how likely it is for planets around them to be hospitable to life.
“There are ten times as many [red dwarfs] in the Milky Way as there are stars like the Sun, and they are twice as likely to have rocky planets as stars like the Sun,” said Thomas Greene, an astrophysicist at NASA’s Ames Research Center and lead author of the study. “But they are also very active — they are very bright when they’re young, and they give off flares and X-rays that can wipe out an atmosphere.”
Previous observations of TRAPPIST-1 b taken by both the Hubble Space Telescope and the Spitzer Space Telescope found no evidence of a puffy atmosphere around the world. But these observations also couldn’t rule out the possibility that the planet was cloaked in a dense, thinner one.
One way to shed more light on whether TRAPPIST-1 b has an atmosphere or not is to measure the planet’s temperature. “This planet is tidally locked, with one side facing the star at all times and the other in permanent darkness,” said Lagage. “If it has an atmosphere to circulate and redistribute the heat, the dayside will be cooler than if there is no atmosphere.”