planetaryus

Planetaryus is a fictional terrestrial exoplanet used in astronomy education and theoretical discussions of planetary formation and climate. It serves as a standard reference in examinations of rocky planets beyond the Solar System and is not tied to any confirmed astronomical object.

In representative models, Planetaryus orbits a Sun-like star (G-type) at roughly 0.9 astronomical units, yielding an orbital period of about 320 days. The planet has a radius of about 1.3 times that of Earth and a mass near 2.5–3 Earth masses, giving a mean density around 5 g/cm³, consistent with a silicate-iron composition.

Atmospheric scenarios for Planetaryus range from a thin secondary atmosphere with modest greenhouse effect to thicker, carbon dioxide–dominated envelopes, depending on volatile inventory and atmospheric escape. In optimistic models, a modest greenhouse could place surface temperatures near Earth's, allowing for stable liquid water under solar-insolation similar to Earth; in cooler or thinner-atmosphere cases, the planet would be largely arid.

Geologically, Planetaryus is described as a world with a solid crust and potential tectonic or volcanic activity in its early history. It features no large moons in many simulations, though some variants allow small satellites. The object remains a hypothetical benchmark for studies of detection methods, atmospheric characterization, and habitability prospects.

See also: exoplanet, habitability, planetary formation.