Steven Swetz, age 11, of Bridgeport, Connecticut, for his question:

Why doesn't gravity pull the earth into the sun?

The sun's enormous gravity would pull the earth and all the other planets into its fiery flames    if it could. Gravity, of course, is a cosmic force, built into every massive object, large or small. A speck of dust has its tiny quota, more massive objects have larger quotas. The mighty gravity of the sun reaches out in all directions. It gets weaker as it goes, but it certainly is strong enough to pull down even the outer planets of the Solar System.

However, speed and motion work against it. The speed of the orbiting earth off¬sets the sun's gravity. Instead of pulling us straight down to the fiery surface, it pulls us around in a curved orbital path. Our orbital speed is just right to match the sun's pull. This balanced tug of war keeps the earth at the same distance. Similar ratios of mass, speed and motion keep all the other planets eternally circling around their separate orbits.