Comet?
Annotation category:
Chapter 7
Comets are, indeed, the remnants of material left over from the formation of
the Solar System 4.54 billion years ago. They range in size from hundreds of
meters to 100 km and are aptly described as dirty snowballs, being composed of
water and other ices with embedded rock-like debris and dust. It is estimated
that more than a trillion of them reside in orbits many billions of miles from
the Sun, far beyond the outermost planets. Occasionally, passing stars or the
interaction among several comets will fling one in toward the Sun. Their
orbits are thus highly elliptical -- they swing very close to the Sun and then are flung back toward the outer reaches of
the Solar System. These we see only once, as their orbital periods are measured
in thousands to millions of years. But in the trip through the planets on the
way to the Sun, the gravitational attraction of a nearby planet can perturb the
comet's orbit such that it gets trapped in the inner solar system, orbiting
once every few to few hundred years. Halley's comet is perhaps the most famous
example, returning as it does every 76 years (it last appeared in 1986, so
you should have a chance to see it after you retire).
