Chapter 12

Question 1

ejecta (from an impact)

Answer 1

Debris ejected by the blast of an impact.

Question 2

Kirkwood gaps

Answer 2

On a plot of asteroid semimajor axes, regions with few asteroids as a result of orbital resonances with Jupiter.

Question 3

Martian meteorites

Answer 3

Meteorites found on Earth that are thought to have originated on Mars.

Question 4

Kuiper belt

Answer 4

The comet-rich region of our solar system that spans distances of about 30–100 AU from the Sun. Kuiper belt comets have orbits that lie fairly close to the plane of planetary orbits and travel around the Sun in the same direction as the planets.

Question 5

K–T event (or impact)

Answer 5

The collision of an asteroid or comet 65 million years ago that caused the mass extinction best known for wiping out the dinosaurs. K and T stand for the geological layers above and below the event.

Question 6

meteor shower

Answer 6

A period during which many more meteors than usual can be seen.

Question 7

plasma tail (of a comet)

Answer 7

One of two tails seen when a comet passes near the Sun (the other is the dust tail). It is composed of ionized gas blown away from the Sun by the solar wind.

Question 8

comet

Answer 8

A relatively small, icy object that orbits a star. Like asteroids, comets are officially considered part of a category known as “small solar system bodies.”

Question 9

chondrites

Answer 9

Another name for primitive meteorites. The name comes from the round chodrules within them. Achondrites, meaning “without chondrules,” is another name for processed meteorites.

Question 10

meteor

Answer 10

A flash of light caused when a particle from space burns up in our atmosphere.

Question 11

dust tail (of a comet)

Answer 11

One of two tails seen when a comet passes near the Sun (the other is the plasma tail). It is composed of small solid particles pushed away from the Sun by the radiation pressure of sunlight.

Question 12

coma (of a comet)

Answer 12

The dusty atmosphere of a comet, created by sublimation of ices in the nucleus when the comet is near the Sun.

Question 13

fireball

Answer 13

A particularly bright meteor.

Question 14

primitive meteorites

Answer 14

Meteorites that formed at the same time as the solar system itself, about 4.6 billion years ago. Primitive meteorites from the inner asteroid belt are usually stony, and those from the outer belt are usually carbon-rich.

Question 15

processed meteorites

Answer 15

Meteorites that apparently once were part of a larger object that “processed” the original material of the solar nebula into another form. Processed meteorites can be rocky if chipped from the surface or mantle, or metallic if blasted from the core.

Question 16

Kuiper belt object

Answer 16

Any object orbiting the Sun within the region of the Kuiper belt, although the term is most often used for relatively large objects. For example, Pluto and Eris are considered large Kuiper belt objects.

Question 17

mass extinction

Answer 17

An event in which a large fraction of the species living on Earth go extinct, such as the event in which the dinosaurs died out about 65 million years ago.