The surface of Mercury

The amazing pictures returned from the Mariner 10 spacecraft showed a world that resembles a moon. It is pocked with craters, contains huge multi-ring basins, and many lava flows. The craters range in size from 100 meters (the smallest resolvable feature on Mariner 10 images) to 1,300 kilometers. They are in various stages of preservation. Some are young with sharp rims and bright rays extending from them. Others are highly degraded, with rims that have been smoothed from the bombardment of meteorites. The largest crater on Mercury is the Caloris basin. A basin was defined by Hartmann and Kuiper (1962) as a "large circular depression with distinctive concentric rings and radial lineaments." Others consider any crater larger than 200 kilometers a basin. The Caloris basin is 1,300 kilometers in diameter, and was probably caused by a projectile larger than 100 kilometers in size. The impact produced concentric mountain rings three kilometers high and sent ejecta 600 to 800 kilometers across the planet. (Another good example of a basin showing concentric rings is the Valhalla region on Jupiter's moon Callisto). The seismic waves produced from the Caloris impact focused onto the other side of the planet and produced a region of chaotic terrain. After the impact the crater was partially filled with lava flows.

Some plains in Mercury are not so heavily cratered. Scientist have named these plains intercrater plains and smooth plains.

Mercuries Atmosphere

Mercury has only trace (very little) amount of the atmosphere it has. The atmosphere of Mercury is extremely thin; indeed, gas molecules in Mercury's atmosphere collide with the surface of the planet more frequently than they collide with each other; for most purposes Mercury can be considered to lack an atmosphere. The "atmosphere" is primarily composed of oxygen, potassium, and sodium.

The atoms that compose Mercury's atmosphere are continually being lost to space, with the average "lifespan" of a potassium or sodium atom being approximately 3 hours (during the Mercurian day—and only half that at perihelion). The lost atmosphere is continually replenished by several mechanisms; solar wind captured by the planetary magnetic field, vapor produced by micrometeor impacts, direct thermal evaporation of the polar ice, and/or outgassing.

Mercuries Temperature

Mercury has temperature ranges from over 400°C at noon (hot enough to melt solid zinc) to less than -150°C at night.

Tough at these temperatures you think you could find ice. Though scorched by the burning heat of the Sun any exposed frozen water would instantly be evaporated.

Recently however, a lunar probe found evidence that ice is stored in craters in the north and south poles on the Moon. This data suggests that deep craters near Mercury's poles may also contain ice deposits.

Mercury The Panet

In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky.

Mercury has been known since at least the time of the Sumerians (3rd millennium BC). It was given two names by the Greeks: Apollo for its apparition as a morning star and Hermes as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Heraclitus even believed that Mercury and Venus orbit the Sun, not the Earth.

Since it is closer to the Sun than the Earth, the illumination of Mercury's disk varies when viewed with a telescope from our perspective. Galileo's telescope was too small to see Mercury's phases but he did see the phases of Venus.

Mercury has been visited by only one spacecraft, Mariner 10. It flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). A new discovery-class mission to Mercury, MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys.

Images from Mariner 10 all pieced together to form a mosaic.
Smooth areas are locations that are unavailable.