The Airless Basalt Crust and Thermal Extremes of Super-Earth LHS 3844 b

Located approximately 48.5 light-years from Earth in the southern constellation of Indus, the exoplanet LHS 3844 b stands as one of the most physically revealing terrestrial targets discovered in modern observational astronomy. Detected in 2018 by NASA’s Transiting Exoplanet Survey Satellite (TESS) and subsequently characterized through high-precision thermal photometry by the Spitzer Space Telescope, this rocky world belongs to the class of extrasolar bodies known as Super-Earths—planets possessing a mass greater than Earth but substantially below that of icy giants like Uranus or Neptune. Measuring roughly 1.32 times the radius of Earth and containing an estimated 2.25 Earth masses, LHS 3844 b orbits an M-dwarf red star at an exceptionally close distance, completing a full revolution in just 11.1 hours.

Unlike many exoplanets whose surfaces are masked beneath dense, opaque atmospheric envelopes, LHS 3844 b offers direct access to its bare, solid crust. Multi-wavelength infrared observations have confirmed that the planet lacks a volatile atmosphere of any significant density. Free from cloud cover, atmospheric scattering, or greenhouse heat retention, LHS 3844 b functions as a pure, unshielded natural laboratory for studying the mineralogy, geodynamics, and thermal physics of massive terrestrial worlds exposed to intense stellar radiation.

Orbital Dynamics and Extreme Tidal Locking

The proximity of LHS 3844 b to its parent star, LHS 3844, defines every facet of its environment. Orbits at a semi-major axis of approximately 0.0062 astronomical units—less than one percent of the distance between Mercury and the Sun—subject the planet to colossal gravitational stress. Over millions of years, tidal dissipation has slowed the planet's rotation into a state of synchronous equilibrium. As a result, LHS 3844 b is tidally locked, permanently presenting the exact same hemisphere toward its host star while the opposing side faces perpetual deep space.

This tidal lock creates a permanent, non-uniform energy balance across the planet's surface. The sub-stellar point—the location on the day side where the host star hangs motionless directly overhead—receives a continuous, unrelenting flux of stellar radiation. Because there is no atmospheric medium to advect thermal energy from the day side to the night side, the heat remains localized. Photometric measurements indicate that the day side reaches peak surface temperatures around 1,040 Kelvin (767°C / 1,410°F), high enough to melt certain metals and scorch silicate rock. Conversely, the night side drops precipitously toward absolute zero, plunging to temperature regimes near 20 Kelvin (-253°C), creating one of the most severe surface thermal gradients recorded on a rocky planetary body.

Geological Composition and Bare Volcanic Basalts

Thermal mapping conducted via Spitzer's Infrared Array Camera (IRAC) at 4.5 microns provided critical constraints on the composition of the planet’s bare surface. The measured phase curve amplitude—the variation in heat emitted by the planet as it reveals different faces to terrestrial telescopes—matches theoretical models of low-albedo, highly absorbent materials. The surface reflects only a small fraction of incident light, yielding an optical albedo comparable to the dark basaltic seas (maria) of Earth's Moon or the dark, carbonaceous regolith of Mercury.

Astronomers infer that the crust of LHS 3844 b is predominantly composed of dark volcanic basalt, high in iron and magnesium silicates. The intense heat on the day side, combined with past periods of gravitational heating during tidal circularization, likely fueled extensive volcanism. Lacking atmospheric weathering agents such as wind or liquid flow, ancient volcanic features—including expansive lava plains, volcanic vents, and solidified effusive flow fields—remain preserved in their primitive state. However, the extreme thermal stress caused by the stark divide between the blazing dayside and frozen nightside generates immense structural fatigue, driving mechanical fracturing, spallation, and tectonic faulting along the twilight terminator region.

Stellar Weathering and Core Density Mechanics

With an average bulk density estimated at 5.4 grams per cubic centimeter—closely mirroring Earth's overall density—LHS 3844 b possesses an internal architecture dominated by a dense, metallic iron-nickel core surrounded by a silicate mantle. Given the planet's elevated mass and higher central pressure, the mantle is expected to undergo vigorous solid-state convection, potentially generating localized thermal plumes that punch through the outer lithosphere.

Without a substantial magnetosphere or protective atmospheric shield, the surface of LHS 3844 b is directly battered by high-energy stellar phenomena. M-dwarf stars like LHS 3844 routinely release intense ultraviolet radiation, X-ray emissions, and energetic coronal mass ejections. Over gigayears, this relentless stellar wind has stripped away any primordial gaseous envelope the planet may have once gathered from its protoplanetary disk. Today, cosmic rays and charged stellar particles slam directly into the exposed silicate regolith, driving space weathering processes that alter the crystal structures of surface minerals and ionize outer atomic layers. LHS 3844 b remains a paramount benchmark object, offering an unprecedented, clear view into the raw, unshielded geology of rocky worlds orbiting low-mass stars throughout the galaxy.