Lynn Selburg, age 10, of Peoria, Ill., For her question:

What exactly is a satellite?

Both a planet and a satellite are solid balls of minerals. Both a planet and a satellite circle the sun. We cannot tell a satellite from a planet by size, for two of Jupiter's moons are bigger than the planet Mercury. The difference lies in their orbits.

A planet circles in a curved line around the sun, while a satellite is the captive of a Planet. The parent planet is a larger body, arid. The satellite cannot escape the pull of its gravity. The satellite must orbit the planet as the planet must orbit the sun. The earth and its satellite, the moon, orbit the sun together. But as they go, the moon is making smaller orbits around the earth, its parent planet.