Planet
Mercury
The swiftest planet, spinning three times every two laps around the Sun.
Mercury races around the Sun every 88 days on the most stretched-out orbit of any planet. It spins slowly, exactly three times for every two orbits, so one sunrise-to-sunrise day lasts about 176 Earth days. Its axis stands almost perfectly upright, so Mercury has no seasons from tilt.
How it moves
- Mercury completes an orbit every 87.97 days at an average speed of 47.36 km/s, faster than any other planet.
- Its orbit is the most eccentric of the planets (0.2056), swinging between about 46 and 70 million km from the Sun.
- Mercury spins once every 58.6 Earth days, exactly 3 rotations for every 2 orbits.
- Because of that 3:2 rhythm, one full solar day (noon to noon) lasts 4,222.6 hours, about 176 Earth days.
- Near perihelion, parts of the surface see the Sun rise briefly, set, and rise again.
- Seen from Earth, Mercury laps us every 115.88 days (its synodic period) and briefly loops backward in our sky.
Facts
- Mean radius
- 2,439.7 km
- Mass
- 3.301e+23 kg
- Surface gravity
- 3.7 m/s²
- Rotation period
- 1407.6 hours
- Orbital period
- 87.969 days
- Average distance from the Sun
- 0.38709893 AU
- Eccentricity
- 0.2056
- Axial tilt
- 0.034°
- Mean orbital speed
- 47.36 km/s
- Known moons
- 0
- Discovered
- Known since antiquity
From some spots on Mercury, the morning Sun rises, sets again, and then rises a second time.
Sources: nssdc.gsfc.nasa.gov, science.nasa.gov