On a journey outwards from the Sun at the centre of our solar system, the first planet we encounter is Mercury, a small, tortured ball of lifeless rock, with no atmosphere to protect it from the deadly radiation of the Sun. No atmosphere as well for meteors to burn up in, subjecting the surface of Mercury to constant pounding from countless bits of cosmic rubble pulled in by the intense gravity well of the Sun. From Mercury, the Sun appears three times as large as it does from Earth, for Mercury is a scant 36 million miles from the blazing solar inferno (compared to our 93 million miles), and the side of the planet facing the Sun is heated to 427 ° C. However, with no atmosphere to hold that heat in, the side of the planet in shadow, facing away from the Sun, drops down to -173 ° C.

Because Mercury is between us and the Sun, we never get to see the entire planet, because we can only see that part of the planet lit by the Sun. When Mercury is between Earth and the Sun, we can't see it at all, unless the alignment is perfect, and we see it as a tiny speck of black moving across the face of the Sun. As it moves to the side, we see a slim crescent that gradually grows larger, like the moon. But before Mercury becomes "full" it passes behind the Sun, and is lost to view. Photo above taken by NASA's Mariner 10 spacecraft.

Mercury is the fastest planet in the solar system. Its year (one complete solar orbit) only lasts 88 Earth days, as it speeds around the Sun at 140,000 miles per hour, compared to Earth's speed of 67,000 mph. This speed is accentuated by the fact that the small size of its orbit so close to the Sun makes it appear to dart back and forth in the sky much quicker than the other planets. So it was only natural for the planet to be named after the fleet footed Roman god Mercury, with wings on his feet, known to the Greeks as the god Hermes, speedy messenger of Zeus. Painting above of Mercury and Athena by Bartholomeus Spranger, circa 1585.

Mercury has no moons. It also has no seasons. Unlike Earth, which is tilted 23 degrees on its axis, Mercury is perpendicular to the plane of its orbit, so the Sun beats down mercilessly on the planet's equator, day after day. The planet's north and south poles, on the other hand, since they are never tilted towards the Sun, are actually believed to contain ice in the bottom of some deep craters that the Sun can't reach.

Mercury revolves very slowly on its axis. One day on Mercury lasts 59 Earth days. Its gravity is about one third that of Earth. If you weighed 100 lbs. on Earth, you would weigh 38 lbs. on Mercury.

With a diameter of 3,032 miles (4,851 kms), Mercury used to be the second smallest planet in the solar system, but when tiny Pluto was demoted to dwarf planet status by the I.A.U. in August, 2006, Mercury officially became the smallest planet in the solar system. As a matter of fact there are four moons in the solar system that are larger than the planet Mercury. The following photo, showing the heavily cratered surface of Mercury, was taken by NASA's Mariner 10 spacecraft in 1975. Click on photo for larger image.

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