James Webb images lava exoplanet

On May 4, a team led by Sebastian Zieba of the Center for Astrophysics | Harvard & Smithsonian and Laura Kreidberg of the Max Planck Institute for Astronomy reported the clearest surface-level evidence yet for a rocky exoplanet observed with the James Webb Space Telescope. The planet, LHS 3844 b, lies about 49 light-years from Earth and is about 30% larger than Earth, according to the researchers. Webb’s mid-infrared observations pointed to a dark, hot and likely airless surface rather than a thick atmosphere. The findings were published in Nature Astronomy and described by the researchers as a step from studying exoplanet atmospheres toward studying exoplanet geology. ### Which planet did Webb examine so closely? LHS 3844 b is a rocky “super-Earth” orbiting a cool red dwarf star once every roughly 11 hours, the research team said. The planet sits extremely close to its star and is believed to be tidally locked, meaning one side permanently faces the star while the other remains in darkness. At about 48.5 to 49 light-years away, the planet is close enough and hot enough for Webb to measure thermal emission from its dayside surface. (nature.com) Earlier work had already found no evidence for a thick atmosphere on LHS 3844 b, making it an unusually favorable target for direct surface characterization. ### What exactly did Webb detect? The James Webb Space Telescope used its Mid-Infrared Instrument, or MIRI, to collect a thermal emission spectrum across wavelengths from 5 to 12 microns, according to the Nature Astronomy paper. (mpia.de) The spectrum was best matched by a dark, low-silica surface such as basalt or other olivine-rich material, the paper said. The Max Planck Institute for Astronomy said the data ruled out a surface like Earth’s silicate-rich crust. (nature.com) The researchers also placed tight limits on carbon dioxide and sulfur dioxide, which the paper said ruled out a substantial atmosphere and recent widespread volcanism. ### Why are some reports calling it a lava world? Reuters and other media reports described the planet as a possible lava world because LHS 3844 b is intensely heated by its star and its dayside is extremely hot. (nature.com) But the research paper itself points more specifically to a dark basalt-like surface shaped by space weathering, not direct confirmation of global surface lava. (mpia.de) The Center for Astrophysics | Harvard & Smithsonian said the surface could resemble basalt or mantle rock, while the lack of volcanic gases argues against recent widespread volcanism. That leaves the picture of a scorched, barren rocky world, with interpretation of any active molten regions remaining limited by the available data. (gmanetwork.com) ### Why is this different from earlier exoplanet work? Nature Astronomy said the result came from the planet’s thermal emission spectrum rather than from atmospheric measurements alone. That matters because most previous detailed exoplanet studies have focused on gases surrounding larger planets or a small number of rocky planets with atmosphere-related constraints. (cfa.harvard.edu) Laura Kreidberg said in the CfA release that deciphering the geological properties of planets orbiting distant stars is the next step in understanding their nature. The result gives astronomers a way to compare distant rocky worlds with familiar bodies such as Mercury, the Moon and basalt-rich terrains in the solar system. (nature.com) ### How firm are the conclusions? The Nature Astronomy paper said the best fit is a dark, featureless, basalt-like surface, but it framed that as an interpretation of the measured infrared spectrum. The same paper tied that interpretation to space-weathered rock and to the absence of strong atmospheric signatures in the data. May 4 marked publication of the study, and subsequent coverage on May 8 and May 17 highlighted the result as the best look yet at a rocky exoplanet’s surface. (cfa.harvard.edu) Future Webb observations by exoplanet teams will test whether similar surface characterization can be extended to other nearby rocky planets. (nature.com 1) (nature.com 2)