For scientists searching for life beyond Earth, rocky planets with atmospheres are among the most promising places to investigate. An atmosphere is essential for maintaining liquid water on a planet's surface. Yet among the more than 6,300 exoplanets cataloged thus far, most are not rocky, and only a small number of known rocky planets appear to possess atmospheres.
Now, researchers have added another world to that short list. In a study published in The Astrophysical Journal Letters, a team led by University of Chicago scientist Brandon Park Coy reports evidence of an atmosphere surrounding HD 3167 b, a rocky super-Earth located 154 light-years away in the constellation Pisces. The intensely hot planet, classified as a "lava world," 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," explained Edwin Kite, UChicago associate professor of geophysical sciences and co-author of the study. "These planets are too hot for life, but by studying them, we can say something about the processes that matter for other rocky worlds." In the Q&A below,Coy, a graduate student in Kite's group and first author on the study, explains why atmospheres on lava worlds are scientifically valuable, how researchers detected evidence for this one, and what they hope to learn next.
What was the goal of the survey that found this atmosphere-bearing exoplanet? One of the driving questions that the James Webb Space Telescope is being used to answer is whether planets orbiting stars much smaller than the sun have atmospheres. It appears that most of those terrestrial planets don't -- they're just bare rock.
But surprisingly, we've found evidence that the majority of lava worlds -- similar in composition to Earth and Venus but much, much hotter -- might have atmospheres. Five terrestrial planets found with atmospheres, including the one described in this study, have been ultra-hot. This planet, however, is the coldest lava world found so far with evidence of an atmosphere.
This is interesting because we're trying to understand the temperature transition between planets with and without atmospheres. The result is the first from a program led by Megan Weiner Mansfield, PhD'21, who's now at the University of Maryland. The goal of the program, which is looking at 10 ultra-hot lava worlds, is to see if there's a critical temperature over which you start seeing planets with atmospheres.
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