NASA’s James Webb Space Telescope (JWST) has observed the distant exoplanet LHS 3844 b in unprecedented detail, revealing a scorched, airless world that closely resembles Mercury or the Moon rather than Earth. Located about 48.5 light-years away, the rocky planet is roughly 30% larger than Earth and orbits a cool red dwarf star at an extremely close distance, completing a full revolution in just under 11 hours.

Because of its proximity to its host star—just about 0.006 AU away, or roughly one-fortieth the distance between Mercury and the Sun—LHS 3844 b is believed to be tidally locked. This means one hemisphere permanently faces the star, enduring constant daylight, while the opposite side remains in perpetual darkness. The dayside experiences extreme heat, with average surface temperatures reaching around 725°C (1,340°F), making it an inhospitable environment.

Using JWST’s Mid-Infrared Instrument (MIRI), researchers measured the heat emitted directly from the planet’s surface. The data suggests a dark, rocky composition dominated by basalt or olivine-rich material, similar to Mercury and the lunar maria. Scientists noted that the spectral readings do not support the presence of an Earth-like silica-rich crust, effectively ruling out geological conditions similar to those on our planet.

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The observations also indicate that LHS 3844 b lacks a significant atmosphere. No evidence of gases such as carbon dioxide or sulfur dioxide was detected, suggesting that even if volcanic activity exists, it is not sufficient to sustain a protective atmospheric layer. As a result, the surface is continuously exposed to intense stellar radiation and micrometeorite impacts, which gradually break down the rock into fine regolith through space weathering.

Researchers emphasized that the planet was not directly imaged. Instead, JWST detected subtle changes in infrared light as the planet orbited its star. When the hot dayside came into view, it slightly increased the total infrared emission; when the nightside faced Earth, that signal disappeared. By analyzing these variations across different wavelengths, scientists constructed a thermal emission profile of the planet.

Published in Nature Astronomy on May 4, 2026, the study highlights JWST’s growing capability to characterize rocky exoplanets beyond the solar system. Scientists described LHS 3844 b as a “hot, barren rock,” underscoring how diverse planetary systems can be, and how unlike Earth many of them truly are.

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