Astronomers have found that TOI-561 b, a planet covered in molten rock, has retained a dense atmosphere. This contradicts earlier assumptions: because of the extreme conditions and its proximity to its star, the planet was thought to have lost its gaseous envelope billions of years ago. The discovery was made by an international team of scientists using the James Webb Space Telescope, and their findings were published in the journal The Astronomical Journal.
TOI-561 b lies 280 light-years from Earth. Observations over 37 hours showed that it reflects about 75 percent of the starlight that falls on it, almost as much as Venus. Scientists believe that such a "sunscreen" may be created by clouds of silicate minerals, such as silicon dioxide. These clouds keep the surface from heating to temperatures one would expect on an exposed rocky planet.
The measurements also showed that the atmosphere carries heat from the dayside, which permanently faces the star, to the nightside. This explains why the dayside is cooler than the models predicted. At the same time, the nightside turned out to be too warm for the heat redistribution alone to account for everything, and this led researchers to suspect the planet's high reflectivity.
It remains unclear how the planet manages to hold on to its atmosphere. One hypothesis is that the gaseous envelope is constantly replenished by evaporation from a global magma ocean. According to Angelica Pietta, an astrophysicist at the University of Birmingham, this ocean may act as one giant volcano, continuously feeding the atmosphere.
The exact composition of the atmosphere is still unknown. It could be a dense layer of carbon dioxide, as on Venus, but under far hotter conditions. Another possibility is an envelope of sulfur dioxide, the gas expelled by the volcanoes of Jupiter's moon Io. Further observations will help determine which of these worlds TOI-561 b more closely resembles.
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