Mike Griffin, age 11, of Montgomery, Alabama, for his question:

How can a comet burn without air?

Fire, as we know it, requires a supply of air. Actually it requires the oxygen in the air. However, our everyday type of fire is not the only blazing, glowing process in the universe. The sun itself burns without air or oxygen. Its blazing furnace is a continuous process of nuclear activity powered by the energy of fusing atoms. A comet does not burn like an earthly campfire either. But neither does it glow by its own radiant nuclear energy. Actually, it is not burning at all.

As the little space traveler comes within range of the sun, its dark dead form is bathed in golden sunbeams. Its fragile solids also feel the pressure of the sun's mighty radiation and it is bombarded by zooming particles of the solar wind. Fragments of the comet are torn loose, gas molecules evaporate from its frozen ices  ¬and all this material is pushed away from the sun. The comet grows a long, filmy tail. Its fine fragments catch and reflect the sunshine. The comet and its tail merely borrow the golden radiance of the sun.