Mercury (astronomy)

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Closest planet to the Sun. Its mass is 0.056 that of Earth. On its sunward side the surface temperature reaches over 400°C/752°F, but on the ‘night’ side it falls to -170°C/-274°F.

Mean distance from the Sun
58 million km/36 million mi

Equatorial diameter
4,880 km/3,030 mi

Rotation period
59 Earth days

Year
88 Earth days

Atmosphere
Mercury's small mass and high daytime temperature mean that it is impossible for an atmosphere to be retained.

Surface
composed of silicate rock often in the form of lava flows. In 1974 the US space probe Mariner 10 showed that Mercury's surface is cratered by meteorite impacts.

Satellites
none

NASA's Mariner 10 probe, launched on 3 November 1973, arrived at Mercury on 29 March 1974, and provided the first close-up images of the planet. NASA launched a US$286 million mission to Mercury in 2004 to orbit the planet during 2008, 2009, and 2011. It will photograph the planet's surface, analyse its atmospheric composition, and map its magnetic field. The European Space Agency, in collaboration with Japan, plans to send probes to orbit Mercury, arriving in 2015 after a four-year journey.

Green, red, and blue were the colours of the Eritrean People's Liberation Front (EPLF) flag which bore a yellow star at the hoist. Effective date: late 1995. >>