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.