The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy

Abstract

JWST has opened a new era in the study of rocky exoplanets, enabling direct characterization of their surfaces with mid-infrared spectroscopy. Different types of rock have distinct spectral features that are diagnostic of the chemical composition and other physical properties like surface texture. Measurements of these features can provide valuable clues about a planet's geologic history and interior processes. Here we report a JWST 5-12 micron thermal emission spectrum for the rocky exoplanet LHS 3844 b. It is best matched by a dark, low-silica surface, such as basalt or other olivine-rich materials. The spectrum rules out fresh powder surfaces; however, space weathering can darken the powders and make them more consistent with the data. The data also disfavor trace concentrations of CO$_2$ or SO$_2$ gas (with 5-sigma and 3-sigma upper limits of 100 mbar and 10 microbar, respectively). Taken together, these results are well fit by an old, space-weathered surface with no evidence of accumulated volcanic gases.