Jeannette Williams, age 11, of Winston Salem, N.C., for her question:
What are asteroids?
Once in a great while, a space traveling asteroid comes close enough to be seen by human eyes. In the dim distant past, a few may have come crashing down like giant boulders from the sky. But such horrible happenings are very rare. In the meantime, countless asteroids zoom merrily around the solar system, keeping in safe and orderly traffic lanes.
The asteroids are mini relatives of the sun's big bulky planets. When one chances to come close enough to be seen, it looks somewhat like a bright star and the word asteroid means a star type object. However, its golden face merely shines with reflected glory from the .sun. Actually, it is a cold object, ranging in size from a pebble to a massive mountain. A few are several hundred miles wide, though none can be compared with the stupendous blazing stars.
Some astronomers call them planetoids, meaning minor planets, which is closer to the truth. The thousands of asteroids that belong to our solar system should be classed with the planets because they travel in planet type orbits. Each one circles the sun along its own path at its own speed. A satellite moon, of course, orbits around a parent planet as the two of them orbit the sun.
For reasons unknown, our teeming planetoids travel through the solar system in two wide belts of their own. One so called asteroid belt is out there at the rim of the solar system near the orbit of the planet Pluto. The asteroid belt we know best is much closer to home, between the orbits of Mars and Jupiter.
When we consider the orbits of the nine planets, most of them seem to be spaced at reasonable intervals. However, the orbits of Mars and Jupiter are separated by an average distance of 340 million miles. Surely in this enormous vacancy there is room for another planet. Instead, the space is occupied by countless planetoids, swirling around the sun like a carousel of golden bees.
Several theories have been suggested to explain our local asteroid belt. Perhaps, when the solar system was formed, the small bodies failed to merge and form a normal size planet. Perhaps they plan to merge and form a planet at some future date.
The most dramatic theory suggests that the asteroids may be fragments of a shattered planet that once existed between Mars and Jupiter. That could account for the wide space between the orbits of these two planets. However, it is estimated that it would take all the material in 200 asteroid belts to make one little moon size planet. At present the asteroid history is a mystery.
Most of the. asteroids travel in fairly round orbits on a level with the sun's equator. Their yearly orbits range from three to six years. A few have eccentric, off center orbits which bring them close to the earth. A few large ones have names. The brightest one we ever see is Vesta, about 248 miles wide. The biggest one we know about is Ceres, estimated to be 488 miles wide. Several others are 50 miles wide but most of them are no bigger than large and smallish boulders.