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15 Cards in this Set

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accretion
the gradual accumulation of matter by an astronomical body, usually caused by gravity
asteroid
any of the rocky objects larger than a few hundred meters in diameter that orbits the sun
asteroid belt
the 1 1/2 astronomical-unit-wide region between the orbits of Mars and Jupiter in which most of the asteroids are found
average density
the mass of an object divided by its volume
comet
a small body of ice and dust in orbit about the sun
crater
a circular depression on a celestial body caused by the impact of a meteoroid, asteroid, comet, or volcano
meteoroid
a small rock in interplanetary space
orbital inclination
the tilt or angle of an object's orbital plane around the sun compared to the ecliptic
planetesimal
primordial asteroidlike object from which the planets accreted
protoplanet
the embryonic stage of a planet when it is growing because of collisions with planetesimals
protoplanetary disks
a disk of material encircling a protostar or a newborn star.
protosun
the sun prior to the time when hydrogen fusion began in its core
solar nebula
the cloud of gas and dust from which the sun and the rest of the solar system formed
solar system
the sun, planets, their satellites, asteroids, comets, and related objects that orbit the sun
terrestrial planet
any of the planets Mercury, Venus, Earth, or Mars; a planet with a composition and density similar to Earth