Definition
Mercury is the smallest and innermost rocky planet of the Solar System. It orbits very close to the Sun, receiving intense energy that strongly affects its surface and surrounding space.
Structure
Its interior contains a dense metallic core occupying much of its volume, surrounded by a mantle and a thin silicate crust. This composition reflects rapid formation and a lack of volatile materials.
Surface and relief
Mercury's surface is covered with craters, smooth plains, and tectonic fractures. The lack of a significant atmosphere leaves the traces of ancient collisions almost untouched.
Rotation and orbit
Its rotation is in a 3:2 spin-orbit resonance with its orbit, meaning it rotates three times for every two orbits around the Sun. This results in a solar day lasting 176 Earth days, with extreme temperature differences between day and night.
Atmosphere and environment
Mercury has only a very thin exosphere made of traces of helium, sodium, and oxygen. This tenuous gaseous layer originates from the solar wind and the breakdown of its surface.
Observation and exploration
Its visible brightness from Earth varies according to its position relative to the Sun. Space missions have mapped its surface and confirmed the presence of metallic elements and ice in the shaded polar regions.