Planet

Mercury

The smallest planet and the closest to the Sun, with the most eccentric planetary orbit.

NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

The smallest planet, where one day from sunrise to sunrise lasts two whole Mercury years.

Mercury's grey, cratered horizon. — Mercury's cratered limb, seen by NASA's MESSENGER spacecraft. Credit: NASA

Mercury is a rocky world only slightly larger than our Moon. It has almost no atmosphere, so its surface swings between about 430 °C by day and −180 °C at night.

It spins exactly three times for every two orbits around the Sun, so one solar day (sunrise to sunrise) lasts two Mercury years. Its large iron core makes it the second densest planet after Earth.

Explore it in the orrery

Data sources

Key facts
Diameter	4,879 km	[1]
Mass	3.301 × 10²³ kg	[1]
Density	5.429 g/cm³	[1]
Surface gravity	3.7 m/s²	Derived from the dataset
Escape speed	4.25 km/s	Derived from the dataset
Rotation (sidereal)	58.6 days	[1]
Length of day	176 days	[2]
Orbital period	88 days	[3]
Axial tilt	0.034°	[2]
Mean temperature	167°C	[2]
Known moons	0	[2]
Average distance from the Sun (semi-major axis)	0.3871 au	[3]

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