Webb telescope finds evidence of atmosphere on hot rocky planet HD 3167 b

Researchers led by University of Chicago scientist Brandon Park Coy reported evidence of an atmosphere surrounding HD 3167 b, a rocky super-Earth located 154 light-years away in the constellation Pisces. The study was published in The Astrophysical Journal Letters, according to ScienceDaily. The planet is classified as a "lava world" and completes an orbit around its star in only one Earth day.

"What's so surprising is that the closer a rocky planet orbits its star, the harder it should be to have an atmosphere, because it's bombarded by stellar wind and gets more high-energy photons from the star. But it seems that many of these lava worlds do," said Edwin Kite, UChicago associate professor of geophysical sciences and co-author of the study. Kite said these planets are too hot for life, but that studying them can say something about the processes that matter for other rocky worlds.

Coy said the James Webb Space Telescope is being used to detect light in the mid-infrared wavelength range to estimate the temperature of exoplanets, which can indicate whether they might have atmospheres. For this study, the team used a method called secondary eclipse, when the planet passes behind its star and researchers measure how much light is lost. Coy said that difference shows how much mid-infrared light comes from the planet itself, which tells researchers how hot the planet is.

Coy said most terrestrial planets orbiting stars much smaller than the sun appear to be bare rock, but that researchers have found evidence the majority of lava worlds might have atmospheres. He said five terrestrial planets found with atmospheres, including this one, have been ultra-hot, and that this planet is the coldest lava world found so far with evidence of an atmosphere. The result is the first from a program led by Megan Weiner Mansfield, PhD'21, now at the University of Maryland, which is looking at 10 ultra-hot lava worlds to see if there is a critical temperature over which planets start having atmospheres.

Coy said directly looking at Earth-like planets for signs of life is out of reach. He said researchers are interested in these planets because they think early Earth might have looked a lot like a lava world.