Chapter 7: Survey of the Solar System

Accretion (229)

addition of matter to a body. Examples are gas falling onto a star and asteroids colliding and sticking together.

asteroid belt (222)

a region between the orbits of Mars and Jupiter in which most of the Solar System’s asteroids are located.

asteroids (222)

a small, generally rocky, solid body orbiting the Sun and ranging in diameter from a few meters to hundreds of kilometers.

Bode’s law (224)

a numerical expression for the approximate distances of most of the planets from the Sun.

Comets (222)

a small body in orbit around the Sun, consisting of a tiny, icy core and a tail of gas and dust. The tail forms only when the comet is near the Sun.

Condensation (228)

the change from gas to liquid. This occurs when a gas cools and its molecules stick together to form liquid or solid particles.

inner planets (220)

a planet orbiting in the inner part of the Solar System. Sometimes taken to mean Mercury, Venus, Earth, and Mars.

interstellar cloud (227)

a cloud of gas and dust in between the stars. Such clouds may be many light years in diameter.

interstellar grains (227)

microscopic solid dust particles in interstellar space. These grains absorb starlight, making distant stars appear dimmer than they truly are.

Jovian planets (221)

one of the giant, gaseous planets: Jupiter, Saturn, Uranus, and Neptune. The name Jovian was chosen because Jupiter’s structure is representative of the other three.

Oort cloud (222)

a vast region in which comet nuclei orbit. This cloud lies far beyond the orbit of Pluto.

outer planets (220)

a planet whose orbit lies in the outer part of the Solar System. Jupiter, Saturn, Uranus, Neptune, and Pluto are outer planets.

planetesimal (230)

one of the numerous small, solid bodies that, when gathered together, form a planet.

solar nebula (228)

the rotating disk of gas and dust from which the Sun and planets formed.

solar nebula hypothesis (227)

the hypothesis that the Solar System formed from a rotating cloud of gas and dust, the solar nebula

Solar System (219)

the Sun, planets, their moons, and other bodies that orbit the Sun.

terrestrial planets (221)

a rocky planet similar to the Earth in size and structure. The terrestrial planets are Mercury, Venus, Earth, and Mars.