Astronomers have found evidence that TOI-561 b, a scorching rocky exoplanet about 280 light-years from Earth, may retain a substantial atmosphere despite receiving intense radiation from its star. Observations from the James Webb Space Telescope (JWST) suggest that reflective silicate clouds could act like a global sunscreen, bouncing much of the starlight back into space while the atmosphere redistributes heat from the permanently illuminated day side to the night side.
An international team of researchers, including astrophysicist Dr Anjali Piett of the University of Birmingham, studied TOI-561 b over 37 hours and observed nearly four complete orbits around its host star.
The observations indicate that the planet may have a significant atmosphere, although its conditions are far too harsh for life as we know it. The atmosphere could help reflect much of the radiation reaching the planet. One possible explanation is a layer of highly reflective silicate clouds that prevents the surface from reaching the extreme temperatures expected on an exposed rocky world.
A lava planet with an atmosphere that should have disappeared
Scientists do not yet know which gases make up TOI-561 b’s atmosphere. One possibility is a thick layer of carbon dioxide, similar to Venus’s atmosphere but under much hotter conditions. Another is an atmosphere like that of Jupiter’s moon Io, which consists mainly of sulfur dioxide released by volcanic activity.
Dr Anjali Piett, assistant professor of astronomy at the University of Birmingham, said: “Our discovery challenges current theory. A rocky planet like TOI-561 b, exposed to large amounts of radiation, would be expected to have lost its atmosphere billions of years ago.”
“Instead, the evidence suggests that the planet still has a significant atmosphere. This raises big questions, such as whether the planet started out with an unusually large supply of gas, or whether oceans of lava covering the surface act as planet-wide volcanoes, constantly feeding the atmosphere.”
James Webb reveals why TOI-561 b is so reflective
Early measurements revealed that TOI-561 b’s dayside was much cooler than expected for a dark, rocky planet orbiting so close to its star. The unexpected temperature suggested that much of the incoming energy was either transferred to the night side or reflected into space before it could heat the surface.
To investigate, the team observed the planet’s entire orbit, enabling researchers to examine its night side for the first time. The same side of TOI-561 b always faces its star, leaving the night side unilluminated by direct starlight. However, measurements showed that the dark hemisphere was not warm enough to account for all the heat lost from the dayside.
Instead, the findings indicate that TOI-561 b reflects about 75% of the starlight that reaches it, a proportion comparable to Venus’s reflectivity.
To determine what could produce such strong reflectance, the researchers compared telescope measurements with computer models of the planet’s climate. The simulations suggest that clouds containing silicate minerals such as silicon dioxide (SiO2) and magnesium silicate (MgSiO3) could form across the dayside. These clouds could act as a natural sunscreen by reflecting incoming radiation before it reaches the planet’s surface.
Professor Lisa Dunn, who led the project at the University of Waterloo in Ontario, Canada, said: “We measured how the planet’s brightness and heat changed throughout its orbit. This technique, known as phase curving, revealed that the planet reflected a large amount of light from the star, redistributing heat around the planet rather than just on the sunlit side. Together, these points to the presence of an atmosphere.”
Can global lava oceans keep the atmosphere alive?
The discovery strengthens earlier evidence collected by Professor Lisa Dunn, Dr Anjali Piette and their collaborators that TOI-561 b has a thick atmosphere that may be continuously replenished by gases escaping from its molten interior.
This process could help explain how some planets maintain atmospheres while enduring intense stellar radiation for billions of years. Rather than simply being lost to space, material from the planet’s vast lava reservoirs may continually replenish its atmosphere.
Researchers now want to determine whether TOI-561 b more closely resembles extremely hot Venus or a more powerful version of the volcanic moon Io. Observations with JWST at longer wavelengths could reveal details about the atmosphere’s chemical composition and help explain how it has survived for so long.
Professor Dunn added: “The next big question we will try to answer is whether TOI-561 b’s atmosphere is similar to Venus, or an extreme version of Venus. Observing the planet at longer wavelengths with JWST may provide insight and help explain how such a hot planet has managed to maintain an atmosphere for billions of years.”
Source: www.sciencedaily.com
