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THE SOLAR SYSTEM
| SOL | MERCURY | VENUS | EARTH | METEORS | MOON | MARS | ASTEROIDS | JUPITER | SATURN | URANUS | NEPTUNE | PLUTO | COMETS |
(Click on image to enlarge)
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| SOL | MERCURY | VENUS | EARTH | METEORS | MOON | MARS | ASTEROIDS | JUPITER | SATURN | URANUS | NEPTUNE | PLUTO | COMETS |
On our journey outwards from the Sun, the first planet we encounter is Mercury, a small, tortured ball of rock, mostly iron, with no atmosphere to protect it from the deadly radiation of the Sun, and as far as we can tell, completely lifeless. 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. The story is told by the planet's heavily cratered surface, seen in the photo above, taken by NASA's MESSENGER spacecraft.
With a diameter of only 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. In fact there are two moons in the solar system that are larger than the planet Mercury,as illustrated below.
Since Mercury is between us and the Sun, we never get to see the entire planet, because, just as in the case of the Moon and Venus, we can only see that part of the planet lit by the Sun. When Mercury is between Earth and the Sun, 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, just like the crescent Moon. But before Mercury becomes "full" it passes behind the Sun, and is lost to view.
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 below of Mercury and Athena by Bartholomeus Spranger, circa 1585.
The painting shows Mercury holding his Caduceus, a staff with two entwined serpents, surmounted by wings. Throughout history, the staff has symbolized commerce and trade, and traditionally carried by messengers, as Mercury himself was the messenger of the gods, and the protector of merchants, shepherds, gamblers, liars and thieves. Unfortunately, in modern times, the Caduceus has been confused with the staff of the famous Greek healer Asclepius (represented by the constellation Ophiuchus), which has only one serpent and no wings, and from ancient times has been the symbol of healing and medicine.
When the Sun rises on Mercury, the temperature almost immediately jumps to a blistering 427 ° C, and stays there, no matter what time of year it is, for Mercury 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. When you jump out of bed you land ten feet away, because you weigh only about a third of what you would weigh on Earth. Most of your waking hours are spent trying to dodge space debris falling from the sky, since there is no atmosphere for it to burn up in. The gravity of the Sun is like a magnet, slowly but surely drawing in all the loose rocky debris in the solar system, and poor little Mercury is right in the line of fire.
Because Mercury's poles are never tilted towards the Sun, if you can make your way to the top or bottom of the planet, you might find some shade, and maybe even some ice inside one of the pole's deep impact craters that the Sun can never reach. For almost three months (Earth-time) an enormous Sun, three times larger than it is on Earth, slowly creeps across the sky. At such a close distance, the Sun's powerful gravity constantly pulling on the tiny planet has slowed its rotation to a crawl, so the Sun stays up in the sky for 88 Earth-days. However, with no atmosphere to hold in the heat, when the Sun finally sets on Mercury, the temperature immediately drops down to -173 ° C, and you had better find a way to keep warm, because the Sun won't rise again for another three months.
A few times a year, Mercury strays far enough away from the Sun in our sky that it can be briefly viewed just before sunrise, or just after sunset, as in the photo below where it shares the sky with Jupiter (the brighter planet on the left), captured March 16, 2011, at the Mexican Skies Observatory, Santa Elena, Oaxaca, Mexico.
Mercury has no moons to light up the night sky, but it has something else. Something no Human eyes have ever seen. It has a light in its sky that we don't. A dazzling blue white light, brighter than any star. For star gazers on Mercury have the planet Earth in their sky, and it is sure to be a dazzling sight. But even closer and brighter than Earth, will be the brilliant cloud covered Venus, the next planet out from the Sun, and the next stop on our journey through the solar system.
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