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Mercury - Rotating Model
Credit: Almond/NASA

Mercury is the closest planet to the Sun. It is also the smallest planet in the Solar System.

Mercury is made mainly of heavy metals, most iron with a rocky crust (mantle). After Earth it is the second most dense planet in our Solar System.

Like the Moon, Mercury has lots of craters but it has no moon of its own. Most of Mercury’s craters were caused by comets and asteroids hitting the planet in the early years of the Solar System being formed. Unlike other planets, Mercury surface is not renewed through volcanic activity so it will always have these ancient craters.

A relief map of Mercury's surface
Credit: NASA

Because Mercury is small and it has little gravity it cannot hold on an atmosphere. As it is so close to the Sun, the solar winds quickly blow away any gases that are released from Mercury. As there is no atmosphere to help control the temperature there are big differences in day-time and night-time temperatures. The surface that faces the Sun can reach about 427 °C with temperatures on the night-time side drop to almost -173 °C.

The first spacecraft to visit Mercury was Mariner 10 in 1974 and it mapped just under half of the planet’s surface. A second mission, MESSENGER, was launched in 2004. During its mission it mapped the surface of Mercury's northern hemisphere in great detail. The image on the left is the map created from the images. The lowest areas are shown in purple, and the highest areas are shown in red.

Planet Data Sheet show »« hide
Facts and FiguresMercuryVenus EarthMarsJupiter SaturnUranusNeptune
Orbital Distance (AU)10.380.72 1.01.525.2 9.4519.230.06
Radius (KM)2,4406,052 6,3783,39771,492 60,26825,55924,746
Mass (Earth Masses)20.0550.82 1.00.11318 95.214.517.1
Year Length
(Earth Days)
88225 365.2568711.9
Day Length
(Earth Days)
176117 0.430.750.67
Surface Gravity (g)30.380.91 1.00.382.34 0.930.921.12
Surface Temperature-200 to
400 °C
460 °C -80 to
50 °C
-150 to
20 °C
-110 °C -140 °C-190 °C-200 °C
Number of moons00 1263 602713
Notes: 1 1 AU (or Astronomical Unit) = 149,600,000 KM and is the mean distance from the Earth to the Sun
2 1 Earth Mass = 5,980,000,000,000,000,000,000,000 KG : 3 1 g = 9.8 m/s2