"Wet lava ball" exoplanet may have an atmosphere, evidence shows

A rocky exoplanet outside the Earth's solar system may have an atmosphere, according to new evidence gathered by NASA researchers.

The exoplanet, known as super-Earth TOI-561b, was discovered in 2020, according to NASA. Scientists have determined that the planet is ultra-hot, with a low density. It is about 1.4 times wider than Earth and orbits the sun in about 11 hours. Its host star is similar to Earth's sun in size and temperature, but the exoplanet is 40 times closer to that star than Mercury is to the sun, NASA said in a news release. Observations suggest the exoplanet has a global magma ocean and that it is surrounded by a thick layer of gas.

The exoplanet's low density has surprised and baffled scientists, NASA said. It may have an unusual composition from planets in Earth's solar system. It could also be surrounded by a thick atmosphere, which would not be expected on an exoplanet with these features. But the James Webb Space Telescope helped scientists gather data that showed that unlikely scenario might be the case.

Researchers used the telescope's Near-Infrared Spectrograph to measure the exoplanet's dayside temperature. If the exoplanet has no atmosphere, scientists estimated its dayside temperature would be about 4,900 degrees Fahrenheit. But the spectrograph found TOI-561b's temperature closer to 3,200 degrees Fahrenheit, far cooler than expected.

Just determining the temperature of the exoplanet doesn't confirm if there is an atmosphere there, NASA said. The magma ocean could cause heat to circulate, or a thin layer of rock vapor could help cool the planet. But neither of those options is likely to account for the difference between the measured temperatures and what scientists expected.

"We really need a thick volatile-rich atmosphere to explain all the observations," said Anjali Piette, a researcher from England's University of Birmingham and a co-author of a study published Thursday that detailed the discoveries.

Piette said an atmosphere would allow gases like water vapor to absorb some wavelengths of light, keeping the telescope's spectrograph from measuring them actually. The exoplanet may also have bright silicate clouds that can reflect starlight to cool the atmosphere, Piette said.

Scientists suspect there may be some form of equilibrium between the exoplanet's atmosphere and its magma ocean, said study co-author Tim Lichtenberg, a researcher from the University of Groningen in the Netherlands.

"At the same time that gases are coming out of the planet to feed the atmosphere, the magma ocean is sucking them back into the interior," Lichtenberg said. "This planet must be much, much more volatile-rich than Earth to explain the observations. It's really like a wet lava ball."

Scientists will learn more about TOI-561b as they study a data set gathered by the Webb telescope after it observed the exoplanet for more than 37 hours. The work will involve mapping the exoplanet's temperature and learning what its atmosphere may be made of.

"What's really exciting is that this new data set is opening up even more questions than it's answering," said Johanna Teske, the paper's lead author and a staff scientist at the Carnegie Science Earth and Planets Laboratory.

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