Astronomers have discovered an unusual exoplanet that combines seemingly incompatible properties: its surface is covered in lava, but the temperature turned out to be significantly lower than expected. According to researchers, the discovery will help better understand what Earth looked like in the first millions of years of its existence.
An international group of astronomers has discovered an unusual exoplanet HD 3167 b, which has become the coldest known lava planet with an atmosphere. The study shows that even in extreme conditions, such worlds can retain an atmosphere, and their study may help scientists better understand the early stages of Earth's formation.
HD 3167 b is located about 154 light-years from our planet and belongs to the class of super-Earths — rocky planets whose mass exceeds that of Earth. It orbits so close to its star that it completes a full revolution around it in just one Earth day.
Due to this positioning, one side of the planet is constantly facing the star, while the other remains in darkness. This state is called tidal locking and is characteristic of many lava worlds.
The discovery was a surprise for researchers. According to existing models, such a close rocky planet should have heated up to maximum possible temperatures and have virtually no atmosphere.
"The closer a rocky planet is to its star, the harder it is for it to retain an atmosphere. However, it seems that many such lava worlds do possess an atmosphere," noted co-author of the study, Edwin Kite, an assistant professor at the University of Chicago.
Measurements were made using the MIRI instrument of the James Webb Space Telescope, which operates in the mid-infrared range. Observations were conducted during a secondary eclipse — the moment when the planet hides behind its star. The analysis of infrared radiation allowed for the estimation of the surface temperature and the detection of signs of an atmosphere.
The data obtained showed that the daytime side of HD 3167 b is significantly colder than predicted by calculations.
According to lead author Brandon Park Koy, the atmosphere likely reflects some of the starlight and transfers heat from the illuminated side to the dark side. This is what allows the planet to remain a lava world while being significantly "cooler" than other known objects of this type.
The discovery is part of a large-scale program in which scientists are studying ten lava worlds using the James Webb Telescope. The main goal of the project is to understand under what conditions such planets can retain an atmosphere.
Researchers believe that the results are important not only for the study of exoplanets. According to modern concepts, shortly after its formation, Earth also underwent a stage of a magma ocean, when its surface was completely molten.
"These planets are too hot for life, but their study helps to understand processes important for other rocky worlds," emphasized Edwin Kite.
Brandon Park Koy added that such objects allow scientists to glimpse into the distant past of our own planet and better understand the conditions that existed in the first millions of years of Earth's history.
The results of the study are published in the scientific journal The Astrophysical Journal Letters.
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