Astronomers have read the surface of a rocky world and found something that looks nothing like Earth. Using the Mid-Infrared Instrument, or MIRI, aboard the James Webb Space Telescope, a team reports that the super-Earth LHS 3844 b is likely a dark, airless ball of basaltic or magmatic rock, closer in character to Mercury or the Moon than to the continental surface of Earth.
The finding marks one of the first direct geological readings of a planet outside our solar system. It pushes JWST beyond atmospheric chemistry into something more fundamental: what rocky exoplanets are actually made of.
A planet that should struggle to keep an atmosphere
LHS 3844 b is a brutal place. The planet orbits its red dwarf host once every 11 hours and is tidally locked, meaning the same hemisphere always faces the star. Its dayside reaches an average temperature of about 1,000 Kelvin, or roughly 725 degrees Celsius. It is about 30 percent larger in radius than Earth and sits only 48.5 light-years away.
Earlier observations with the Spitzer Space Telescope had already suggested that the planet lacked a thick atmosphere. The new JWST MIRI data strengthen the case, picking up thermal radiation from the planet’s hot dayside in a way that favors a dark, barren, atmosphere-free surface. What MIRI sees is not a temperate terrestrial cousin. It is a hot rock exposed directly to space.
Reading rock from 48 light-years away
The infrared spectrum tells a specific story. Different minerals emit infrared light differently, especially in the mid-infrared range where MIRI operates. By splitting the planet’s thermal emission between roughly 5 and 12 micrometers, astronomers can compare the signal against laboratory and model spectra of rocks and minerals known from Earth, the Moon and Mars.
Earth’s continental crust is strongly associated with granitic, chemically evolved material produced by a long history of water-assisted melting, recycling and tectonic processing. LHS 3844 b’s spectrum does not match that kind of Earth-like crust.
Instead, the data point toward basaltic or magmatic rock: dark, iron- and magnesium-rich material closer to terrestrial basalt, lunar basalt or mantle-derived rock. The best-fitting models include extended solid areas of basaltic or magmatic minerals, potentially rich in magnesium and iron and including minerals such as olivine.
What the darkness rules out
The absence of an Earth-like granitic crust carries a heavy implication. On Earth, continents are downstream products of plate tectonics, water and repeated chemical differentiation. Subduction recycles crust. Water helps the system operate. Melting and solidifying separate lighter minerals toward the surface.
Strip away that kind of crust and you strip away one of the signatures of Earth-like geological machinery. The researchers argue that Earth-like plate tectonics either does not operate on LHS 3844 b or is ineffective there. They also suggest the planet likely contains little water.
That matters beyond a single exoplanet. Plate tectonics is widely discussed as one possible ingredient in long-term climate regulation and, perhaps, planetary habitability. LHS 3844 b is far too hot and close to its star to be Earth-like. But it gives astronomers a rare look at what can happen to rocky worlds around red dwarfs when atmosphere, water and surface recycling are stripped out of the story.
Two stories, one surface
The spectrum points to a dark surface, but it does not fully settle how that surface got dark. Two different histories can produce similar light.
In the first, the surface is relatively young and geologically active. Recent or ongoing volcanism could have repaved the dayside with fresh basaltic material, leaving broad areas of dark solid rock.
In the second, the surface is old and has spent a long time being altered by stellar radiation, particles and micrometeorite impacts. Planetary scientists call this space weathering. The Moon’s regolith is the familiar case. These processes can break down rock into finer material and darken the upper layer by adding iron and carbon, making the surface look more like what MIRI observes.
The team cannot completely separate the two possibilities from the current data. But one result tilts the interpretation. Sulfur dioxide is often associated with volcanic outgassing, and MIRI did not detect it in amounts the researchers expected would be visible if recent volcanism were strong. That makes the old, space-weathered surface the favored explanation for now.
A new mode of exoplanet science
Until recently, exoplanet characterization usually meant transit spectroscopy: watching how starlight filters through a planet’s atmosphere. That approach fails when there is no atmosphere to read. MIRI’s sensitivity in the mid-infrared opens a second channel: the planet’s own thermal emission.
The same instrument has been used to measure the dayside temperature of TRAPPIST-1 b, another rocky world orbiting a red dwarf. What LHS 3844 b adds is the possibility of reading the surface itself. Geology, not just meteorology.
The result also fits into a wider push in exoplanet science. Recent work in Nature Astronomy has argued that JWST’s mid-infrared observations can, in principle, distinguish between different kinds of rocky surfaces, including basaltic materials and minerals that could point to past or present water. LHS 3844 b is now one of the clearest test cases for that emerging field.
The longer arc
Red dwarfs host many of the rocky planets astronomers can study most easily, partly because their small size makes orbiting planets easier to detect. But close-in worlds around red dwarfs face a harsh environment: intense irradiation, tidal locking, atmospheric erosion and frequent stellar activity in many systems.
LHS 3844 b is an extreme example. It is not a habitable-zone planet and should not be treated as a direct stand-in for every rocky world around a red dwarf. But it does show one possible endpoint: a hot, dark, likely airless rocky planet whose surface has been exposed to space long enough to become more Mercury-like than Earth-like.
The next generation of observatories will push the question further. NASA’s planned Habitable Worlds Observatory is being designed to study Earth-sized planets in the habitable zones of nearby stars and search for signs of atmospheres, oceans and potentially life.
That mission will inherit a question LHS 3844 b sharpens: how often does a rocky planet end up like Earth, with continents, oceans and a churning interior, and how often does it end up like this, a sun-baked basalt sphere holding its silence?
For related coverage, see Space Daily’s reporting on a nearby super-Earth discovered by IAC astronomers, an earlier super-Earth in a promising habitable zone, and analysis of how JWST is being used to study Earth-like worlds.
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