Earth Science Chapter 28 Vocab

retrograde motion

a planet's apparent back- ward movement in the sky.

meteorite

a small frag- ment of an orbiting body that has fallen to Earth, generating heat; does not completely burn up in Earth's atmosphere and strikes Earth's surface, sometimes causing an impact crater.

dwarf planet

an object that, due to its own gravity, is spherical in shape, orbits the Sun, is not a satellite, and has not cleared the area of its orbit of smaller debris.

ellipse

an oval that is centered on two points called foci; the shape of planets' orbits.

scarp

cliff on Mercury; similar to those on Earth but much higher.

liquid metallic hydrogen

form of hydrogen with both liquid and metallic properties that exists as a layer in the Jovian atmosphere.

zone

high, cool, light-colored cloud that rises and flows rapidly in the Jovian atmosphere.

gas giant planet

large, gaseous planet that is very cold at its surface; has ring systems, many moons, and lacks solid surfaces—Jupiter, Saturn, Uranus, and Neptune.

belt

low, warm, dark-colored cloud that sinks and flows rapidly in the Jovian atmosphere.

meteor shower

occurs when Earth intersects a cometary orbit and comet particles burn up as they enter Earth's upper atmosphere.

terrestrial planet

one of the rocky-surfaced, relatively small, dense inner planets closest to the Sun—Mercury, Venus, Earth, and Mars.

meteoroid

piece of interplanetary material that falls toward Earth and enters its atmosphere.

eccentricity

ratio of the distance between the foci to the length of the major axis; defines the shape of a planet's elliptical orbit.

Kuiper belt

small solar system bod- ies that are mostly rock and ice, lies outside the orbit of Neptune, 30 to 50 AU from the Sun, most probably formed in this region.

comet

small, eccentrically orbiting body made of rock and ice which consists of a nucleus, a coma, and one or more tails that point away from the Sun.

planetesimal

space object built of solid parti- cles that can form planets through collisions and mergers.

meteor

streak of light produced when a meteoroid falls toward Earth and burns up in Earth's atmosphere.

astronomical unit

the average distance between the Sun and Earth, 1.496 × 108 km or 1 AU.