JWST Mid‑Infrared Spectrum Indicates Basaltic Surface, Little Atmosphere on Rocky Exoplanet LHS 3844 b

NASA’s James Webb Space Telescope has produced a mid-infrared spectrum of the rocky exoplanet LHS 3844 b that points to a dark surface made of low-silica rock, consistent with basalt or olivine-rich material, while finding no evidence for a substantial accumulated atmosphere. The result marks an important early step beyond simply detecting rocky worlds and toward directly probing what their surfaces are made of.

The finding appears in a paper, “The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy,” posted to arXiv on April 30, 2026, as arXiv:2605.00100. The arXiv entry says the paper was accepted for publication in Nature Astronomy on April 8, 2026. The first authors listed on arXiv are Sebastian Zieba and Laura Kreidberg.

The study reports a JWST thermal-emission spectrum spanning about 5 to 12 microns, a mid-infrared range that contains diagnostic features from rock-forming minerals. That makes it especially useful for asking not just whether a rocky exoplanet has an atmosphere, but what kind of surface lies below. In the paper’s abstract, the authors say the spectrum is “best matched by a dark, low-silica surface, such as basalt or other olivine-rich materials.” They also say the data rule out fresh powder surfaces, though space weathering — the gradual alteration of exposed material by radiation and micrometeorite impacts — could darken powdery rock and make it more consistent with the observations. As the abstract puts it, “Taken together, these results are well fit by an old, space-weathered surface with no evidence of accumulated volcanic gases.”

The atmospheric constraints are more limited and need careful wording. According to the abstract, the data disfavor carbon dioxide and sulfur dioxide gas, with an upper limit of 100 millibars for CO2 at 5-sigma significance and 10 microbars for SO2 at 3-sigma. Under the authors’ modeling assumptions, that means the observations are inconsistent with CO2 atmospheres at or above about 0.1 bar. It does not mean the planet is proven to have no atmosphere at all, but rather that the team found no evidence of accumulated volcanic gases in the spectrum they measured.

LHS 3844 b has been a high-priority target for this kind of work since its discovery in 2018. The planet is rocky and about 1.3 times Earth’s radius. It orbits its star in just 11.1 hours and lies about 14.9 parsecs, or 48.5 light-years, from Earth. Earlier observations suggested it was probably airless or nearly airless, which is important because a thick atmosphere can mask the thermal signal from the surface below.

That background came from a 2019 Spitzer phase-curve study, which measured a very large temperature difference between the planet’s day and night sides and concluded that LHS 3844 b likely lacks a thick atmosphere. The new JWST result builds on that picture. Rather than stopping at the question of whether the planet has a substantial atmosphere, it uses mid-infrared data to begin distinguishing among possible rocky surfaces — a notable demonstration of how exoplanet science is moving toward direct surface characterization.