In a groundbreaking observational study employing the Mid-Infrared Instrument (MIRI) aboard the James Webb Space Telescope (JWST), astronomers have unveiled the mysterious nature of the exoplanet LHS 3844 b, revealing it as a dark, airless rocky super-Earth with striking similarities to our Solar System’s Mercury. This discovery marks a pivotal advancement in exoplanetary science, shifting the focus from atmospheric characterization to detailed geological investigations of distant terrestrial worlds. The results, spearheaded by former Max Planck Institute for Astronomy (MPIA) doctoral researcher Sebastian Zieba and MPIA Director Laura Kreidberg, were published in Nature Astronomy on May 4, 2026.
LHS 3844 b orbits its host star — a cool red dwarf — in an extraordinarily close orbit, completing a revolution every 11 hours. This tight gravitational embrace results in tidal locking, where one hemisphere perpetually faces the star, basking in relentless daylight with surface temperatures soaring around 1000 Kelvin, approximately 725 degrees Celsius. Situated just 48.5 light-years away, this proximity offers an unparalleled glimpse into the characteristics of rocky planets outside our Solar System.
Employing JWST’s unmatched sensitivity, the researchers were able to detect the infrared emission directly emanating from the planet’s searing hot surface. Intriguingly, rather than a vibrant, atmosphere-rich world, LHS 3844 b resembles an inert, barren rock — dark and devoid of an atmosphere. This crucial insight was gleaned not by direct imaging, but through precision measurements of the combined brightness fluctuations of the star and planet system, as the planet’s position changes relative to Earth.
By dissecting the planet’s infrared radiation between 5 and 12 micrometers into finely resolved spectral bins, the team created a detailed emission spectrum. This spectrum, augmented with previous data from the Spitzer Space Telescope, enabled the astronomers to compare the observed wavelengths against laboratory models of minerals found on Earth, the Moon, and Mars. These comparisons decisively excluded compositions similar to Earth’s silicate-rich crust, such as granite, pointing towards a fundamentally different geological makeup.
Insights from terrestrial geological science suggest that Earth’s silicate crust forms through protracted tectonic and hydrological processes, requiring plate tectonics and significant water presence to recycle mantle material and generate lighter minerals at the surface. The absence of such a crust on LHS 3844 b implies a tectonically inactive world with minimal water content, indicating a geologic environment starkly contrasting with Earth’s.
The spectral data strongly favor a surface dominated by basaltic or magmatic rocks, mineralogically abundant in magnesium and iron, potentially enriched with olivine. Interestingly, the data suggest the presence of solid, extended rock formations or crushed rubble rather than fine powdery grains. The implications are profound: without an atmosphere to shield it, the surface endures relentless space weathering from intense stellar radiation and bombardment by micrometeorites, which gradually darkens and modifies surface materials.
A nuanced statistical fit to the infrared spectrum paints two plausible geological scenarios. One posits freshly exposed basaltic rock, resurfaced recently by geological activity such as widespread volcanism. The alternative scenario envisages an older, more heavily weathered regolith — a layer of dark, fine sedimentary rock fragments akin to the lunar surface — reflecting a long period of geological dormancy. Both scenarios maintain the dark and airless nature of the planet but differ in their interpretations of geological dynamism.
Further differentiating between these two models, the research team searched for signs of volcanic outgassing, particularly sulphur dioxide (SO₂), a hallmark byproduct of active volcanism. The absence of SO₂ absorption features in the MIRI data heavily favors the latter scenario — a geologically quiescent planet with a heavily weathered surface. This suggests LHS 3844 b may closely resemble Mercury, marked by an ancient crust and a surface sculpted over eons by space weathering rather than active geophysical processes.
Moving forward, the astronomers are poised to leverage additional JWST observations equipped to distinguish subtle variations in surface texture by analyzing how light is emitted or reflected from solid slabs versus powdered material. Surface roughness influences emission angles, enabling the team to refine their models and decisively identify the geological state of LHS 3844 b. This technique, adapted from asteroid studies within our Solar System, heralds a new era in exoplanetary geology with the potential to unlock the mysteries of countless rocky worlds.
This research, integrating observational astronomy with planetary geology, not only enriches our understanding of exoplanet surfaces but challenges existing paradigms about tectonic activity and planetary evolution beyond the Solar System. By revealing a barren, basalt-like world subjected to intense space weathering, the study underscores the diversity of rocky exoplanets and the myriad evolutionary paths they may follow.
The success of this study also showcased the collaborative effort behind JWST and MIRI, involving numerous institutions and international partners including NASA, the European Space Agency (ESA), and the Canadian Space Agency (CSA), alongside scientific bodies like the Max Planck Society and several universities. The groundbreaking data harnessed by JWST’s MIRI instrument reinforces its status as the premier observatory for illuminating the cosmos in unprecedented detail.
As the astronomical community anticipates forthcoming JWST observation cycles, the methodologies demonstrated in this study set a robust precedent for characterizing the geological properties of rocky exoplanets. With each successive insight, humanity edges closer to unraveling the complex histories and potential habitability of Earth-like worlds scattered across our galaxy.
Subject of Research: Not applicable
Article Title: The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy
News Publication Date: 4-May-2026
Web References: https://doi.org/10.1038/s41550-026-02860-3
References: Zieba, S., Kreidberg, L., et al. (2026). The dark and featureless surface of rocky exoplanet LHS 3844 b from JWST mid-infrared spectroscopy. Nature Astronomy.
Image Credits: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington (cropped)
Keywords
Exoplanet, LHS 3844 b, James Webb Space Telescope, MIRI, mid-infrared spectroscopy, rocky super-Earth, space weathering, basaltic surface, planetary geology, tidal locking, volcanism, sulphur dioxide
