JWST Peers at a Rocky Super-Earth's Surface for the First Time, Finding a Dark, Airless World That Looks Like Mercury
Astronomers used JWST's MIRI to directly study the surface geology of LHS 3844 b, a super-Earth 48.5 light-years away, revealing a basaltic, atmosphere-free world resembling Mercury — a first for exoplanet science.
Overview
For the first time, astronomers have used the James Webb Space Telescope to directly study the surface geology of a rocky exoplanet beyond our solar system — and what they found is a world that more closely resembles Mercury than Earth. The target, a planet called LHS 3844 b located 48.5 light-years away, is a dark, airless super-Earth with a basaltic surface devoid of any detectable atmosphere. The findings, published May 4, 2026 in Nature Astronomy, mark a shift in exoplanet science from studying atmospheres to reading the geology of distant rocky worlds directly.
What Astronomers Found
LHS 3844 b is a super-Earth roughly 30% larger than Earth, orbiting a cool red dwarf star every 11 hours at a distance of only about three stellar diameters from the star’s surface, according to ScienceDaily. Because it orbits so close to its host star, the planet is tidally locked, with one hemisphere permanently bathed in starlight and the other perpetually dark. Its sunlit side bakes at approximately 1,000 Kelvin — around 725 degrees Celsius or 1,340 degrees Fahrenheit.
The research team, led by Sebastian Zieba of the Center for Astrophysics | Harvard & Smithsonian and principal investigator Laura Kreidberg, Director of the Max Planck Institute for Astronomy, analyzed infrared light emitted from the planet’s dayside using JWST’s Mid-Infrared Instrument (MIRI), measuring emission between 5 and 12 micrometers across three separate secondary eclipses observed in 2023 and 2024, as reported by Space.com. By comparing those readings against spectral models of rocks from Earth, the Moon, and Mars, the team characterized the planet’s surface composition for the first time, according to Phys.org.
The results were unambiguous. As Kreidberg described in the EurekAlert press release: “Thanks to the amazing sensitivity of JWST, we can detect light coming directly from the surface of this distant rocky planet. We see a dark, hot, barren rock, devoid of any atmosphere.”
The data pointed to a basaltic surface rich in magnesium and iron — potentially containing olivine — rather than the granite-like, silica-rich crust found on Earth, according to SciTechDaily. Zieba noted in the same press release that the absence of such a silicate crust has broader implications: “Since LHS 3844 b lacks such a silicate crust, one may conclude that Earth-like plate tectonics does not apply to this planet, or it is ineffective. This planet likely only contains little water.”
Why the Surface Is So Dark
The team considered two competing explanations for the planet’s dark appearance, as described by Astrobiology.com. The first scenario is that the planet’s surface is covered in geologically fresh, dark basaltic rock from widespread recent volcanic activity. The second is that the surface has been darkened over billions of years by space weathering — the same process that darkens regolith on Mercury and the Moon — indicating a world that is geologically inactive.
The absence of any detectable sulfur dioxide in the infrared spectrum argues against active volcanism, according to Phys.org. The research team favors the second scenario: that LHS 3844 b is an old, geologically quiet world whose surface has been darkened by prolonged exposure to space weathering, making it resemble an enlarged Mercury, as reported by SciTechDaily.
The Debrief also notes that the analysis “confidently ruled out” an Earth-like silicate-rich crust, which requires both tectonic activity and water acting as a geological lubricant.
A New Frontier for Exoplanet Science
The study, titled “The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy” and published with DOI 10.1038/s41550-026-02860-3, represents a methodological milestone for the field. Until now, exoplanet characterization focused almost exclusively on atmospheric chemistry. This is the first time mid-infrared spectroscopy has been used to read the geology of a rocky world from its surface thermal emission.
Kreidberg indicated the technique is not a one-off, telling The Debrief: “We are confident the same technique will allow us to clarify the nature of LHS 3844 b’s crust.”
The result lands at a particularly fertile moment for rocky-world exoplanet research. JWST has recently upended assumptions about what atmospheres rocky planets can and cannot retain — previously reported when the telescope found unexpected volatile signatures on worlds thought too hot and irradiated to hold one — and last week detected methane in the atmosphere of the temperate giant TOI-199b, the first such chemistry mapped for that class of world. The LHS 3844 b result adds a third dimension to that work: a planetary body where the lack of any atmosphere lets astronomers look all the way down to the rock.
What We Don’t Know
While the team favors the space weathering interpretation, the two surface scenarios cannot yet be definitively separated by current data alone, as noted by Astrobiology.com. Future JWST observations of LHS 3844 b’s nightside temperature, or additional spectral coverage, could help resolve whether the surface hosts any ongoing or recent geological activity.
The paper’s technique — reading crustal composition from mid-infrared thermal emission during secondary eclipses — is also optimized for hot, atmosphere-free worlds. Applying it to cooler or more distant rocky planets where surface temperatures are lower will require significantly longer observation times or future instruments.
Nonetheless, as Astrobiology.com observed, the ability to determine crustal composition on a rocky world nearly 50 light-years away represents a paradigm shift — from cataloguing exoplanet atmospheres to reading the geologic record of worlds far beyond our solar system.