• The images returned by the space probe Mariner 10 in 1974 and 1975, revealed that Mercury has a cratered, rocky, surface, rather like the Moon's but without the larger, smoother areas. It has an enormous crater, the Caloris Basin, which is over 813 miles (1,300 km) across.



• Until 1974 almost nothing was known about the surface of Mercury. Whenever it is visible from Earth it is never far from the Sun, low down in the sky. That makes it very difficult to get a good view of Mercury in a telescope.



• In 1974 the American space probe Mariner 10 passed within a few hundred miles of the surface of Mercury and relayed back to Earth thousands of images. This first flyby was in March 1974. It was followed by two more, in September 1974 and March 1975. The images returned during these encounters have been used to map about 35% of Mercury's surface.



• Mercury is the second smallest planet after Pluto, which is half its size. It is the planet nearest the Sun, orbiting faster than any other. A complete journey around the Sun takes Mercury only 88 days at an average speed of about 107,000 mph (172,000 km/h). Earth travels at about two-thirds this speed and Pluto at only about one-tenth.



• Astronomers think Mercury has an iron core accounting for about 70% of its mass and 75% of its diameter. This core is a little bigger than our Moon.



• The mantle surrounding the core is thought to be a layer of rock about 400 miles(640km) thick.



• Mariner 10 detected atoms of sodium and tiny amounts of helium and hydrogen near the surface of Mercury, but this gas can hardly be called an atmosphere: the best vacuum that can be made in a laboratory on earth has more gas in it.



• During a day on Mercury, Mercury's distance from the Sun varies between 43 million miles (70 million km) and 35 million miles (56 million km). An observer on Mercury would see the Sun increase in size and then decrease again.



• At midday on Mercury, with the Sun overhead, the temperature reaches around 800�F(420�C). Three Earth months after sunrise, the Sun sets and the cold night begins. With no atmosphere to act like a blanket and hold in the warmth, the temperature plunges to -300�F(-180�C).

Mercury Facts

This page hosted by � Get your own Free Home Page