James Webb discovers a scorching lava planet with a “giant sunscreen”

An international team of researchers, including Dr. Anjali Piette, an astrophysicist at the University of Birmingham, reported the findings in The Astronomical Journal. Using the James Webb Space Telescope (JWST), the scientists monitored a rocky exoplanet called TOI-561 b, located approximately 280 light-years from Earth. Over 37 hours, they observed nearly four complete orbits around its host star.

The observations indicate that TOI-561 b may be surrounded by a substantial atmosphere, although its conditions would be far too hostile for life as we know it. This atmosphere appears to help the planet reflect much of the radiation coming from its star. 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 planet. The atmosphere also appears to move heat from the permanently illuminated dayside toward the nightside, further reducing temperatures on the star-facing side.

A Lava Planet With an Atmosphere That Should Have Disappeared

Scientists still do not know exactly which gases make up the atmosphere of TOI-561 b. One possibility is a thick layer of carbon dioxide, resembling the atmosphere of Venus but under much hotter conditions. Another is an atmosphere dominated by sulfur dioxide, a gas released by volcanic activity on Jupiter's moon Io.

Dr. Anjali Piette, Assistant Professor in Astronomy at the University of Birmingham, said: "Our discovery challenges current theories. We would expect a heavily irradiated rocky planet like TOI-561 b to have lost its atmosphere billions of years ago.

"Instead, the evidence suggests it still has a significant atmosphere today. This raises major questions such as whether the planet started with an unusually large supply of gases or if the ocean of molten rock covering its surface, acts as a planet-wide volcano that is constantly feeding its atmosphere."

James Webb Reveals Why the Planet Is So Reflective

Earlier measurements revealed something puzzling about TOI-561 b. Its dayside was significantly cooler than researchers predicted for a dark, rocky planet orbiting so close to its star. That unexpected temperature suggested that much of the incoming energy was either being transferred to the nightside or reflected back into space before it could heat the surface.

To investigate, the team observed the planet throughout its orbit, allowing them to examine its nightside for the first time. Because the same side of TOI-561 b always faces its star, the nightside receives no direct starlight. However, the measurements showed that this darker hemisphere was not warm enough to explain all the missing heat.

The findings instead indicate that TOI-561 b reflects approximately 75% of the starlight reaching it, a remarkably high proportion comparable to Venus.

To determine what could produce such strong reflectivity, the researchers compared the telescope measurements with computer models of the planet's climate. Their simulations suggest that clouds containing silicate minerals, including silicon dioxide (SiO2) and magnesium silicate (MgSiO3), may form over the dayside. If present, these clouds could reflect incoming radiation before it reaches the surface, functioning as a natural sunscreen.

Professor Lisa Dang, 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 a phase curve, revealed that the planet reflects a significant amount of light from its star, and that heat is being redistributed around the planet instead of only on the sunlit side. Together, these point to the presence of an atmosphere."

Could a Global Ocean of Lava Keep the Atmosphere Alive?

The new findings strengthen earlier evidence gathered by Professor Lisa Dang, Dr. Anjali Piette, and their collaborators that TOI-561 b has a thick atmosphere that may be continually replenished by gases escaping from its molten interior.

That possibility could help explain how the planet has maintained an atmosphere despite enduring intense radiation from its star for billions of years. Rather than simply losing its gases to space, the planet's vast reservoir of molten rock may be constantly releasing new material into the atmosphere.

Researchers now hope to determine whether TOI-561 b is more like an extremely hot Venus or a much more intense version of the volcanic moon Io. Additional observations with JWST at longer wavelengths could reveal important details about the atmosphere's chemical composition and help resolve the mystery of its long-term survival.

Professor Dang added: "The next big question we will seek to answer is whether TOI-561 b's atmosphere resembles Venus or an extreme version of lo. Observing the planet at longer wavelengths with JWST could give us insights and help explain how a planet this hot has held on to an atmosphere for billions of years."