Definition
A rocky planet without an atmosphere is a body mainly composed of minerals and rocks, lacking a stable gaseous envelope. Its surface is in direct contact with the cosmic vacuum.
Structure
It has a solid crust made of silicates and metals, often covered with craters. Beneath lies a rigid mantle and sometimes a metallic core, reflecting its planetary origin.
Surface and conditions
The absence of an atmosphere causes extreme temperature variations between illuminated and dark regions. Micrometeorite impacts and solar wind strike the surface directly, slowly breaking it down.
Evolution
Without an atmosphere, there are no erosion processes, winds, or rains. The appearance remains almost unchanged except for new impacts. Such a planet may be an ancient remnant of a stellar system.
Observation and limits
These worlds display the primitive forms of planetary terrain. Their study helps understand the formation of solid crusts, but their conditions exclude the presence of surface liquid or life.