The Bare Volcanic Plains of Tidally Locked Exoplanet LHS 3844b

Orbiting a dim M-dwarf star just 48 light-years away, LHS 3844b presents a rare opportunity for planetary science. Unlike many exoplanets that mask their true character behind thick, insulating blankets of gas, this world has been stripped bare. It is a testament to the brutal efficiency of stellar radiation when a planet orbits too close to its host, leaving its surface exposed to the raw vacuum of space and the unyielding glare of a nearby sun.

LHS 3844b is a super-Earth, roughly 1.3 times the radius of our own planet, but it possesses a density profile suggesting a composition dominated by rock and iron. Due to its extreme proximity to its star—completing a full orbit in just 11 hours—it has succumbed to tidal locking. This gravitational synchronization ensures that one hemisphere is perpetually scorched by a noon-day sun that never sets, while the other is trapped in a permanent, starless winter.

The Absence of an Atmospheric Shield

Data from secondary eclipse observations confirm the most striking feature of this world: the lack of a substantial atmosphere. On most planets, winds redistribute heat from the day-side to the night-side, moderating temperatures. On LHS 3844b, the heat remains locked precisely where it falls. The day-side registers temperatures soaring to over 1,000 degrees Kelvin, while the night-side plunges into a cryogenic void. Without an atmosphere to transport this thermal energy, the planet acts as a static heat map of stellar flux.

The Bare Volcanic Plains of Tidally Locked Exoplanet LHS 3844b - Section 2 overview

Geologically, the surface is expected to be basaltic, similar to the solidified lava plains of the lunar maria or the plains of Mercury. The intense, consistent heating of the sub-stellar point likely drives profound tectonic stress. As the rock expands under extreme temperatures, the crust may fracture, creating deep thermal basins and ridges that define the geography of the day-side. There is no weather, no erosion from wind, and no hydrological cycle; the landscape is carved only by the slow, grinding influence of geological cooling and radiant heat.

The Surface Perspective

Standing on the surface of this world, the experience is defined by the stark, unforgiving contrast between light and dark. The ground consists of jagged, vitrified rock, darkened by eons of solar wind interaction. Because there is no atmosphere to scatter light, the sky is a deep, absolute black, populated by sharp, unblinking points of light that represent distant background stars. There is no diffuse glow, no horizon haze, and no transition from blue to black; the shadow cast by a rock is a crisp, impenetrable void of darkness.

The Bare Volcanic Plains of Tidally Locked Exoplanet LHS 3844b - Section 3 overview

The ground beneath is composed of vast fields of cooling basaltic glass and pulverized volcanic dust. The lack of air means that every micro-impact from micrometeorites remains preserved indefinitely, scarring the ground in a static, timeless tapestry of cratering. As one moves toward the terminator line—the region between day and night—the temperature gradient steepens dramatically, resulting in a zone of extreme thermal contraction and stress fractures, where the basalt crust has buckled under the localized strain of extreme, uneven expansion.

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