Chapter 24: Meteorites, Asteroids, and Comets

falls

A meteorite seen to fall.

find

A meteorite that is found but was not seen to fall.

Iron meteorites

A meteorite composed mainly of iron–nickel alloy.

Stony-iron meteorites

A meteorite that is a mixture of stone and iron.

Stony meteorites

A meteorite composed of silicate (rocky) material.

Carbonaceous chondrites

Stony meteorite that contains both chondrules and volatiles. These may be the least altered remains of the solar nebula still present in the Solar System.

selection effect

An influence on the probability that certain phenomena will be detected or selected, which can alter the outcome of a survey.

Widmanstätten patterns

Bands in iron meteorites large crystals of nickel–iron alloys.

chondrites

A stony meteorite that contains chondrules.

achondrites

Stony meteorite containing no chondrules or volatiles.

chondrules

Round, glassy body in some stony meteorites; thought to have solidified very quickly from molten drops of silicate material.

CAIs

Calcium–aluminum-rich inclusions found in some meteorites.

meteor showers

An event lasting for hours or days in which the number of meteors entering Earth’s atmosphere suddenly increases. The meteors in a shower have a common origin and are traveling through space on nearly parallel paths.

radiant

The point in the sky from which meteors in a shower seem to come.

sporadic meteors

A meteor not part of a meteor shower.

S-type asteroids

A type of asteroid common in the inner asteroid belt, with relatively high reflectivity and reddish color, probably composed of rocky material.

M-type asteroids

A type of asteroid with relatively high reflectivity and grayish color, probably composed primarily of metal.

C-type asteroids

A type of asteroid common in the outer asteroid belt, with very low reflectivity and grayish color, probably composed of carbonaceous material.

Kirkwood gaps

Regions in the asteroid belt in which there are very few asteroids; caused by orbital resonances with Jupiter.

Apollo–Amor objects

Asteroid whose orbit crosses that of Earth (Apollo) and Mars (Amor).

Near-Earth Objects (NEOs)

An asteroid or comet in an orbit that passes near or intersects Earth’s orbit that could potentially collide with Earth.

Trojan asteroids

Small, rocky body caught in Jupiter’s orbit at the Lagrange points, 60 degrees ahead of and behind the planet.

centaurs

An outer Solar System body with an orbit entirely within the region of the Jovian planets, for example Chiron, that orbits between Saturn and Uranus.

Hirayama families

Family of asteroids with or bits of similar size, shape, and orientation; thought to be fragments of larger bodies.

gas tail

The tail of a comet produced by gas blown outward by the solar wind.

nucleus

The central core of an atom containing protons and neutrons; carries a net positive charge.

dust tail

The tail of a comet formed of dust blown outward by the pressure of sunlight.

Oort Cloud

The cloud of icy bodies—-extending from the outer part of our Solar System out to roughly 100,000 from the Sun—that acts as the source of most comets.

Chicxulub

The buried crater associated with the mass extinction event at the end of the age of dinosaurs, named after the town in the coastal region of Mexico’s Yucatán peninsula near the center of the crater.

coma

The glowing head of a comet.