Astronomers Analyze Surface of Nearby Super-Earth LHS 3844 b

Astronomers have analyzed the surface composition of the rocky exoplanet LHS 3844 b using the Mid-Infrared Instrument (MIRI) on the James Webb Space Telescope (JWST). This super-Earth is 30% larger than Earth. It orbits a cool red dwarf star approximately 48.5 light-years away.

LHS 3844 b completes an orbit in about eleven hours. It is tidally locked, meaning one side always faces its star. This creates a constant dayside with an average temperature of about 725 degrees Celsius. Researchers observed infrared radiation from this hot dayside. They found the planet is a dark, hot, barren rock without an atmosphere.

The infrared spectrum data was compared with models of rocks and minerals. This ruled out a composition similar to Earth's crust, which is rich in silicates like granite. Earth's silicate-rich crust forms through prolonged refinement, tectonic activity, and water. The absence of such a crust on LHS 3844 b suggests a lack of Earth-like plate tectonics or water.

The dark surface indicates a composition similar to terrestrial or lunar basalt, or Earth's mantle material. These materials are rich in magnesium and iron. Statistical analysis showed that solid areas of basalt or magmatic rock best fit the observations. Crushed material like rocks or gravel also fit the data. Grains or powders were inconsistent due to their brighter appearance.

Without an atmosphere, planets undergo space weathering from stellar radiation and meteorite impacts. This process can darken the surface by adding iron and carbon. Two scenarios emerged: a fresh surface from recent geological activity like volcanism, or a weathered surface with a dark regolith layer. The absence of sulfur dioxide, a gas linked to volcanism, suggests the latter. This indicates LHS 3844 b may resemble Mercury, with a surface altered by long periods of geological inactivity and space weathering.