James Webb finds LHS 3844 b 725°C

Science & Vie reported on May 18 that James Webb Space Telescope observations have characterized the surface of LHS 3844 b, a rocky exoplanet about 48.5 light-years from Earth. The report described a dayside temperature of about 1,000 Kelvin, or roughly 725 degrees Celsius, on a world that circles its red-dwarf star once every 11 hours. The findings match a Nature Astronomy paper and a May 4 release from the Center for Astrophysics | Harvard & Smithsonian that said the planet appears dark, airless and basalt-like. ### Why are astronomers paying attention to this one planet? LHS 3844 b stands out because it is a rocky planet, not a gas giant, and James Webb was able to probe the composition of its surface rather than just search for atmospheric gases. The Center for Astrophysics said the work was led by Sebastian Zieba, a NASA Sagan Fellow at the Center for Astrophysics | Harvard & Smithsonian, and Laura Kreidberg, director at the Max Planck Institute for Astronomy. (science-et-vie.com) Nature Astronomy described the result as a thermal-emission spectrum from 5 to 12 micrometers, measured with Webb’s Mid-Infrared Instrument, or MIRI. That spectrum was best matched by a dark, low-silica surface such as basalt or other olivine-rich rock, according to the paper abstract and the CfA release. ### How hot is 725°C in practical terms? The reported average dayside temperature is about 1,000 Kelvin, equivalent to roughly 725 degrees Celsius or 1,340 degrees Fahrenheit. (cfa.harvard.edu) Science & Vie said that is hot enough to melt pure aluminum, underscoring that this is not a temperate rocky world. (nature.com) The same report said the planet is tidally locked, meaning one hemisphere always faces the star. That produces a permanent dayside under constant heating and a permanent nightside that does not receive starlight. (science-et-vie.com) ### What did Webb actually detect? Webb did not photograph the ground directly. The Center for Astrophysics said researchers inferred the surface from infrared light emitted by the hot dayside and from repeated changes in the combined brightness of the star and planet. Science & Vie said the spectrum showed a smooth emission pattern without strong bands, consistent with a very dark surface. (science-et-vie.com) The article said the statistical analysis pointed to basalt or magnesium- and iron-rich igneous rock, possibly dominated by olivine. (cfa.harvard.edu) ### Does the planet have air, clouds or active volcanism? The Center for Astrophysics release said Kreidberg described LHS 3844 b as “a dark, hot, barren rock, devoid of any atmosphere.” The Nature Astronomy abstract said the data also set tight upper limits on carbon dioxide and sulfur dioxide, disfavoring a substantial atmosphere. (science-et-vie.com) The Nature Astronomy abstract added that the measurements were consistent with an old, space-weathered surface and showed no evidence of accumulated volcanic gases. Science & Vie similarly reported no sign of a habitable environment and described the surface as more like frozen basaltic lava than anything resembling Earth’s crust. ### How unusual is this result for exoplanet science? (cfa.harvard.edu) Science & Vie said this was the first time a telescope had directly described the mineral surface of a distant rocky world. The CfA release said moving from atmospheric characterization to geological characterization is the next step in understanding rocky planets around other stars. (nature.com) The paper is now published in Nature Astronomy, and the named researchers on the reported study are Sebastian Zieba and Laura Kreidberg. Further follow-up will likely come from the same teams and from additional Webb observations of other nearby rocky planets. (nature.com) (science-et-vie.com)