Mercuryn

Mercuryn is a fictional terrestrial planet featured in speculative astronomy and science fiction. In its canonical setting, Mercuryn orbits a Sun-like star at a distance of about 0.34 astronomical units, producing extreme diurnal temperature swings and a short orbital period around 60 days. The planet is described as a small, rocky world with a predominantly basaltic crust and a dense, metal-rich interior.

Mercuryn has a radius about 0.92 times that of Earth and a mass near 0.7 Earth masses, yielding a surface gravity close to 0.9 g. Its density is approximately 5.4 g/cm3, consistent with a metal-rich mantle and crust. The axial tilt is low, resulting in modest seasonal variation. The surface shows extensive plains of solidified lava, impact craters, and high-relief volcanic zones. The planet's magnetic field is weak or intermittent in the sources describing Mercuryn.

Mercuryn lacks a substantial atmosphere; what exosphere exists is thin and transient, composed mainly of light elements. Daytime temperatures can exceed 800 °F (427 °C) at equatorial latitudes, while nights are frigid due to rapid radiation into space. No indigenous life is described in the setting, though minerals and geologic activity are well documented. In-universe exploration includes orbital missions such as the Orbital Reconnaissance Vehicle and surface probes that mapped the crust, confirmed basaltic volcanism, and identified metallic ore concentrations. The science supports a world of interest primarily for planetary geology rather than habitability.