|Matter | Pages 64-65 ||
The Sun's strong gravitational pull dooms comets to return again and again to the inner solar system. Each time they lose more mass and shine a bit less brightly. Some comets fizzle after hundreds or thousands of such orbits and drift like small asteroids among the inner planets. Others split into pieces like poorly packed snowballs if they wander too close to the Sun. Still others plunge into the Sun and melt in a flash--the ultimate in solar system recycling.
As for Comet Hale-Bopp, our descendants will see it again in the year 4380. Its return trip will be much faster, thanks to a gravitational tweak in its orbit when the comet passed Jupiter in 1995. Between now and then hundreds of other bright comets will streak across the sky. Each will remind its admirers of how easily matter can transform from ancient ice to a mist that vanishes into space on the breath of the solar wind.MATTER'S Many Guises
Comets are beautiful examples of a rule of thumb that applies to most matter in the universe: Sooner or later it changes into something else. Consider the wooden furniture in your home, which seems permanent enough. But not long ago the furniture was a tree, and before that it was a seedling that grew by using sunlight to convert water, carbon (continued)