asteroid: A large piece of rock that was formed at the same time as the Sun and the planets.

atmosphere: The various gases that surround a planet or other body in space. A denser atmosphere better protects the planet from outside factors.

axis: The imaginary line running from pole to pole through a planet's center. A planet spins (rotates) along its axis.

belt: One of the darker bands of clouds in Jupiter's atmosphere.

comet: A small ball of rock and ice that orbits the Sun. When it gets close to the Sun, some of the ice melts and releases gases. These gases form a tail behind the comet.

core: The centermost part of a planet.

crater: An irregular oval-shaped hole created by a collision with another objection, usually a meteorite.

density: An object's mass divided by its volume.

gravitational field: The area of space affected by a planet's gravity.

gravity: The force that pulls objects toward the center of a planet or other body in space.

magnetic field: The area surrounding a planet in which magnetic force is felt.

magnetosphere: The area of space around a planet that is affected by he planet's magnetic field.

mass: The amount of matter or material in an object.

meteorite: A particle of dust or rock that hits the surface of another object, such as a moon or planet.

orbit: The curved path followed by one body going around another body in space.

radiation belt: A region around Jupiter where the electrically charged particles that make up solar wind congregate. The particles are trapped by Jupiter's magnetic field.

solar system: The Sun and all the objects that orbit it, such as planets, moons, asteroids, and comets.

solar wind: A stream of particles that are given off by the Sun.

space probe: An unmanned spacecraft carrying scientific instruments that orbits the Sun on its way to one or more planets. It may fly past a planet it has been aimed at, orbit the planet, or even land on the planet.

terrain: The physical features of a piece of land.

volume: The total amount of space an object occupies.

zone: One of the lighter bands of clouds in Jupiter's atmosphere.