Summary of Key Ideas

Asteroids

Comets

Meteoroids, Meteors, and Meteorites

WHAT DID YOU THINK?

  • Are the asteroids a former planet that was somehow destroyed? Why or why not? No. The gravitational pull from Jupiter prevented a planet from ever forming in the asteroid belt. Also, the present-day total mass of the asteroids is much less than even the mass of tiny Pluto, a dwarf planet.
  • How far apart are the asteroids on average? The distance between asteroids averages 1 million km.
  • How are comet tails formed? Of what are they made? Ices in comet nuclei are turned into gas by absorbing energy from the Sun. Debris is released in this process. Sunlight and the solar wind push on the gas and dust, creating the tails.
  • In which directions do a comet’s tails point? The gas tails of comets point directly away from the Sun; their dust-sized debris tails make arcs pointing away from the Sun.
  • What is a shooting star? A shooting star is a piece of space debris plunging through Earth’s atmosphere—a meteor. It is not a star.