Mercury, as seen by MESSENGER.
Mercury is the first planet in the Solar System. It is also the smallest and most eccentric of the eight planets.
Orbit and Rotation
Mercury orbits the sun in about 88 days. However, the planet takes 58 days, 15 hours, and 30 minutes to rotate once, the second slowest day on any planet in the Solar System!
Mercury's Thin Atmosphere
Mercury's atmosphere is 42% molecular oxygen, 29% sodium, 22% hydrogen, 6% helium, and 0.5% potassium, with traces of other gases.
Mercury's "Weird Terrain"
Mercury has a rocky surface with many craters, resembling Earth's moon. These craters came from asteroids and comets blasting into the planet's surface during the Solar System's formation 4.6 billion years ago.