Mercury

Mercury

Planet· orbits the Sun

Mercury is the smallest planet and the closest to the Sun. Airless and heavily cratered, it swings through extreme temperatures and has the most eccentric orbit of the eight planets.

Open in 3D viewSee Mercury in the live, interactive 3D map

Key facts

Mass
3.30 × 10²³ kg
0.0553 M⊕
Radius
2,440 km
38% of Earth's radius
Surface gravity
3.7 m/s²
38% of Earth's
Day length
58.6 days
Year
87.97 Earth days
Distance from Sun
0.387 AU
Moons
None

Science

Physical

Mass
3.30 × 10²³ kg · 0.0553 M⊕
Radius
2,440 km · 38% of Earth's radius
Density
5,427 kg/m³ · 5.4× water
Surface gravity
3.7 m/s² · 38% of Earth's
Escape velocity
4.25 km/s · 38% of Earth's
Axial tilt
0.03 °

Orbital

Distance from the Sun
0.317 AU
Semi-major axis
0.387 AU
Eccentricity
0.2056
Inclination
28.55 °
Orbital period
88.0 days
Perihelion
0.307 AU
Aphelion
0.467 AU
Mean orbital velocity
47.9 km/s

Rotation

Rotation period
58.6 days

Atmosphere

Composition
Tenuous exosphere (O, Na, H, He, K)
Surface pressure
1.0 × 10-10 Pa

Temperature

Minimum
100 K (-173 °C)
Mean
440 K (167 °C)
Maximum
700 K (427 °C)

Composition

Bulk composition
Large iron core (~85% of the radius), thin silicate mantle and crust

Radiation & temperature

Insolation
6.67 S⊕ · 6.67× the sunlight Earth receives
Bond albedo
0.09 · reflects 9% of incoming sunlight
Equilibrium temperature
437 K (164 °C)
Measured mean temperature
440 K (167 °C)
Surface magnetic field
300 nT · 1% of Earth's

Discovery & history

First known
Known since antiquity
Name
The Roman messenger god, for its swift motion across the sky.

Mercury has been known since at least Sumerian times, recorded over 3,000 years ago. Because it never strays far from the Sun it is hard to see, and ancient Greeks at first thought the morning and evening apparitions were two different objects. It was named for the fleet-footed messenger of the gods. Its true nature — a cratered, airless world — was revealed only by Mariner 10 in 1974–75 and mapped fully by MESSENGER after 2011.

  1. 1974Mariner 10Flyby

    First spacecraft to visit Mercury; three flybys in 1974–75 revealed a cratered world with a magnetic field.

Images

Mercury in enhanced colour, imaged by MESSENGER
NASA / Johns Hopkins APL / Carnegie Institution (public domain) · Wikimedia Commons
Happy Little Crater on Mercury
NASA/GSFC · NASA Image Library
From Orbit, Looking toward Mercury's Horizon
NASA/GSFC · NASA Image Library
On the Edge of Mercury
NASA/GSFC · NASA Image Library
Smooth Plains in Mercury's North
NASA/GSFC · NASA Image Library
Spectacular Color . . . with Better Yet to Come
NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington · NASA Image Library
MESSENGER View of Mercury's Caloris Basin
NASA/GSFC · NASA Image Library
A Terminator View from Mercury Flyby 2
NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington · NASA Image Library

Images from open archives · credit shown per image