Page 7 - Curriculum Visions Dynamic Book

The giant planets have two types of moons orbiting them. There are those that follow a more or less circular orbit in the same plane as the planet’s equator and revolve in the same direction as their parent planet. They are called the regular satellites. They were probably formed from
gas and dust at the same time as the planet. But there are others that do not fit into the general pattern. Most of these moons are small and orbit far away from their parent. They have different orbits and often rotate in the opposite direction from their parents. They are known as irregular satellites. They are probably small bodies that were captured by the planets after they had formed elsewhere in the solar system.
The moons are enveloped in thin, flat rings. The rings themselves are made of countless billions of tiny rocky bodies. They might be the debris left over after the planet and larger moons formed. Alternatively, they might be debris left over after collisions of meteoroids with a former moon or moons. In the former case the rings would be as old as the planets, but in the latter case the rings would be younger. At the moment, we simply have no measurements to tell us which of these alternatives is true.
asteroid belt The collection of asteroids that orbit the Sun between the orbits of Mars and Jupiter.
boiling point The change of state of a substance in which a liquid rapidly turns into a gas without a change in temperature.
compound A substance made from two or more elements that have chemically combined.
condensation The change of state from a gas or vapor to a liquid.
core The central region of a body.
element A substance that cannot be decomposed into simpler substances by chemical means.
equator The ring drawn around a body midway between the poles.
gravity The force of attraction between bodies.
meteoroid A small body moving in the solar system that becomes a meteor if it enters the Earth’s atmosphere.
radiation The transfer of energy in the form of waves (such as light and heat) or particles (such as from radioactive decay of a material).
satellite An object that is in an orbit around another object, usually a planet.
space Everything beyond the Earth’s atmosphere.
 An artist’s impression
of what it might look like from the moon Enceladus (see page 42) looking toward Saturn and its rings of dust and moons.
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