James Webb images lava world exoplanet

Astronomers using the James Webb Space Telescope have produced one of the clearest infrared looks yet at the surface of a rocky exoplanet, concluding that LHS 3844 b is a dark, hot and likely airless world. A paper published in *Nature Astronomy* reported that the planet's 5-12 micron thermal emission spectrum is best matched by a dark, low-silica surface such as basalt or other olivine-rich material. The data also set tight limits on carbon dioxide and sulfur dioxide, ruling out a substantial atmosphere, according to the paper. LHS 3844 b is about 48.5 light-years from Earth and about 30% larger than Earth, according to the Max Planck Institute for Astronomy and NASA. ### Which planet did Webb study, and how extreme is it? LHS 3844 b orbits a red dwarf star and completes one orbit in about 0.5 days, according to NASA's exoplanet catalog. NASA lists the planet's radius at 1.286 times Earth's and its mass at 2.37 Earth masses, placing it in the super-Earth category. The Max Planck Institute for Astronomy said the planet circles its star once in roughly 11 hours and is tidally locked, so the same hemisphere always faces the star. (nature.com) That permanent dayside reaches about 1,000 Kelvin, or roughly 725 degrees Celsius, the institute said. ### What exactly did Webb detect? The *Nature Astronomy* paper reported a 5-12 micron thermal emission spectrum for LHS 3844 b. (science.nasa.gov) The authors said the spectrum is best explained by a dark, basalt-like surface rather than by a thick atmosphere. Sebastian Zieba, the study's lead author, and Laura Kreidberg, the principal investigator, analyzed the planet with Webb's Mid-Infrared Instrument, or MIRI, according to the Max Planck Institute for Astronomy. (mpia.de) The institute said the observations revealed "a dark, hot surface without an atmosphere" and indicated a surface likely composed of basalt or mantle rock. (nature.com) ### Why are researchers calling it a lava world? The planet's temperature and proximity to its star put it in the class of rocky worlds often described as lava planets, where the dayside is intensely heated. The new result did not report a global ocean of molten rock observed directly, but it did show a hot rocky surface whose infrared signature matches materials associated with volcanic rock. (mpia.de) Nature's exoplanet coverage said the JWST spectrum points to a dark, basalt-like surface shaped by space weathering. It also said the measurements rule out recent widespread volcanism, because the data place tight limits on gases such as CO2 and SO2 that would be expected in a substantial atmosphere. ### How does this differ from earlier Webb exoplanet results? (mpia.de) NASA says Webb's exoplanet work has largely focused on atmospheres, including water vapor, carbon dioxide and sulfur dioxide around larger planets and thermal emission from small rocky worlds. In earlier observations, Webb found evidence that some rocky planets such as 55 Cancri e may have an atmosphere, while other rocky planets such as TRAPPIST-1 b appear to lack a significant one. (nature.com) LHS 3844 b adds a different kind of measurement: a direct constraint on surface composition for a rocky exoplanet. The Max Planck Institute for Astronomy said this pushes Webb beyond atmospheric studies toward probing the geology of distant rocky planets. ### What comes next for this line of research? Laura Kreidberg said in the institute's release, "We see a dark, hot, barren rock, devoid of any atmosphere." (esa.int) The paper appears in *Nature Astronomy*, where researchers described the result as a thermal emission spectrum of a rocky exoplanet's surface rather than an atmospheric detection. NASA's exoplanet catalog continues to list LHS 3844 b as a confirmed planet discovered in 2019, with an orbital period of about 0.5 days and a radius of 1.286 Earth radii. (mpia.de) Future Webb studies of similarly hot rocky planets are likely to test whether LHS 3844 b is unusual or one example of a broader class of dark, airless super-Earths. (science.nasa.gov)