Elizabeth Girady, age 10, of Alvadore, Oregon, for her question:
Where did the comet begin?
Kohoutek failed to show us a golden comet tail, as promised. But the little visitor from space gave astronomers a golden opportunity to study it. The evidence they gathered points to where it came from, way out beyond the farthest planet. It also points to where, when and how it began, along with billions of other space traveling comets.
More than 200 years ago, Edmund Halley figured out where many comets come from and where they go. Though without computers or a powerful telescope he had the help of the great Isaac Newton who had explained how gravity governs the paths of heavenly bodies. Halley scanned old records to learn how often certain bright comets had returned and predicted their repeat performances.
These were periodic comets that return to swing around the sun on regular schedules. Between visits they chug around long oval orbits out among the planets. Some return on schedule every few years, others have periods of decades and even centuries. However, Kohoutek was a different sort of comet.
Astronomers now know that there are billions of comets and most of them are way out in space beyond the farthest planets of the Solar System. The orbit of little Pluto is about 3,670 million miles from the sun. It is estimated that comet Kohoutek started its journey to the sun from five million million miles out in space. Perhaps its last visit was five million years ago and maybe it will return in about 90,000 years.
Most astronomers think that Kohoutek and billions of other comets were born way out there in the bleak cold realms beyond the farthest planets. They seem to be smallish, hazy bodies that froze around the edges of an enormous cloud of dusty gases. Gradually this cosmic cloud condensed to form the starry sun, the solid planets and other members of the Solar System.
Most of Kohoutek's teeming relatives stayed out beyond the planets.
But all of them move with the Solar System through the Galaxy. Sometimes an outer comet is nudged off course. Then the combined gravity of the sun and the planets urge it toward the center of the Solar System.
This happened when Kohoutek began its long journey to visit the sun. It dawdled past the orbits of Neptune and Pluto, Uranus and Saturn. Gradually, its speed increased and in January 1973 it passed Jupiter. In early December it was hurtling toward the sun at 100,000 miles per hour. On December 28, when only 13 million miles from the blazing sun, it rushed around a U turn at 250,000 miles per hour. Now its speed is slowing down as it departs for the other end of its long orbit.
Astronomers are almost certain that Kohoutek began five billion years ago, when gases way out beyond the Solar System froze to form billions of covets. They also think that it visited the sun five million years in the distant past. This time, however, the gravity of the planets most likely changed its old path. Its new orbit is smaller and a return visit to the sun is predicted to occur after about 90,000 years.