Terrestrial Planet

Mercury

Mercury is the smallest planet in our solar system and the closest to the Sun. With virtually no atmosphere to retain heat, it experiences the greatest temperature variations of any planet, from scorching hot to freezing cold.

Equatorial Diameter

4,879 km

Temperature

473°C (day) / -183°C (night)

Mass

$3.3 \times 10^{23} \text{ kg}$

Surface Gravity

$3.7 \text{ m/s}^2$

Rotation Period

59 Earth Days

Solar Day

176 Earth Days

Planetary Structure & Atmosphere

Mercury is the smallest planet in the Solar System and the closest to the Sun. It has a metallic core that occupies about 85% of the planet's radius, surrounded by a silicate mantle and crust. Its atmosphere is extremely thin, composed of atoms blasted off the surface by solar wind and micrometeoroid impacts, creating a transient exosphere.

Exosphere Composition

Oxygen ($O_2$)42.0%

Sodium ($Na$)29.0%

Hydrogen ($H_2$)22.0%

Helium ($He$) & Potassium7.0%

Cosmic Weight & Age Matrix

70 kg Human Weight

26.6 kg

0.38x Earth Gravity

20 Earth Years Equivalent

83.0 Years

Mercury Orbital Years (88 Days)

Escape Velocity

4.25 km/s

0.38x Earth Escape Velocity

Scientific Discoveries

Orbits the Sun at a mean distance of 60.3 million km.
Completes an orbit around the Sun in just 88 Earth days, the fastest of all planets.
The surface features numerous narrow ridges, which may have formed as Mercury's core and mantle cooled and contracted after the crust had solidified.
Despite its proximity to the Sun, water ice exists in permanently shadowed craters at its poles.
From Earth, Mercury appears as a morning or evening star, but it can be hard to see. It is best observed twice a year: in spring at dusk and in autumn before dawn.
It has a very thin atmosphere, called an exosphere, composed mostly of oxygen, sodium, and hydrogen.