The Dense Iron Core and Scorched Surface of GJ 367 b

Orbiting the red dwarf star GJ 367 in the constellation Vela, the exoplanet GJ 367 b represents one of the most extreme examples of planetary density discovered to date. Situated a mere 31 light-years from Earth, this sub-Earth-sized world is defined by its extraordinary composition, which suggests a massive, exposed metallic core left behind by the stripping of a primordial outer mantle. With an orbital period of just 7.7 hours, the planet is locked in a rapid, high-energy dance with its host star, enduring constant stellar flux that keeps its dayside surface at temperatures exceeding 1,500 degrees Celsius.

The physical profile of GJ 367 b is dominated by its iron content. Astronomical data indicates that this planet possesses a density significantly higher than that of Earth. Models suggest that GJ 367 b is composed of approximately 85 percent iron by mass. This extreme interior architecture dictates the planet’s geological reality: it is a world devoid of thick volatile atmospheres, as the intense heat and stellar wind from its parent star have long since evaporated any light gases that might have once clung to its surface. What remains is a rugged, cratered, and thermally reactive landscape of solidified silicates and iron-rich crust.

The Dynamics of Extreme Tidal Coupling

Due to its extreme proximity to its host star, GJ 367 b is tidally locked, meaning one hemisphere faces the star in perpetual, blistering daylight while the other remains cast in eternal shade. This atmospheric asymmetry creates a thermal gradient of immense proportions. On the dayside, the surface is essentially a global lava ocean or a superheated regolith, where incident radiation keeps the surface temperature high enough to maintain rocky material in a molten or semi-molten state.

Conversely, the nightside of GJ 367 b experiences a sharp drop in temperature. Although the planet’s high thermal inertia prevents the nightside from plummeting to absolute zero, the lack of a substantial atmosphere to redistribute this heat ensures a persistent, cold, and solid dark-side environment. This bifurcation creates a distinct geological boundary between the illuminated and shadowed hemispheres, characterized by rapid expansion and contraction of crustal material near the terminator line, where the planet’s day meets its night.

Surface Morphology and Crustal Composition

At the microscopic level, the surface of GJ 367 b is a mosaic of basaltic plains and iron-oxide dust. Lacking the buffering effects of a thick atmosphere, the surface is continuously bombarded by cosmic rays and stellar particles, which chemically alter the mineralogy of the crust over time.

High-resolution spectroscopic signatures imply a surface lacking in light elements such as hydrogen or helium. Instead, the terrain is likely composed of complex metallic salts and refractory oxides that can withstand the intense thermal environment. The surface roughness is governed by the cooling rates of these materials; where volcanic activity persists, slow-cooling flows create expansive, flat basaltic sheets. In regions of extreme temperature fluctuations, the surface exhibits signs of thermal cracking, with deep fissures revealing the dense, iron-rich interior of the planet. This world serves as a testament to the extremes of planetary evolution, providing a glimpse into the skeletal remains of worlds that have been reduced to their most essential metallic components.