Chapter 14 Solar System Debris

Kuiper belt

a region in the plane of the solar system outside the orbit of Neptune where most short-period comets are thought to originate

comet

a small body, composed mainly of ice and dust, in an elliptical orbit about the Sun; as it comes close to the sun, some of its material is vaporized to form a gaseous head and extended tail

trans-Neptunian object

a small, icy body orbiting beyond the orbit of Neptune; Pluto and Eris are the largest currently known examples

Earth-crossing asteroid

an asteroid whose orbit crosses that of Earth; these are also called Apollo asteroids, after the first asteroid of this type discovered

coma

an effect occurring during the formation of an off-axis image in a telescope; stars whose light enters the telescope at a large angle acquire comet-like tails on their images; the brightest part of a comet, often referred to as the "head"

hydrogen envelope

an invisible sheath of gas engulfing the coma of a comet, usually distorted by the solar wind and extending across millions of kilometers of space

meteorite

any part of a meteoroid that survives passage through the atmosphere and lands on the surface of Earth

asteroid

one of thousands of very small members of the solar system orbiting the Sun between the orbits of Mars and Jupiter; often referred to as "minor planets"

Trojan asteroid

one of two groups of asteroids which orbit at the same distance from the Sun as Jupiter, 60 degrees ahead of and behind the planet

meteoroid swarm

pebble-sized cometary fragments dislodged from the main body, moving in nearly the same orbit as the parent comet

asteroid belt

region of the solar system, between the orbits of Mars and Jupiter, in which most asteroids are found

micrometeoroid

relatively small chunk of interplanetary debris ranging in size from a dust particle to a pebble

Kuiper-belt object

small icy body orbiting in the Kuiper belt

Oort cloud

spherical halo of material surrounding the solar system out to a distance of about 50,000 AU; where most comets reside

dust tail

the component of a comet's tail that is composed of dust particles

nucleus

the solid region of ice and dust that composes the central region of the head of a comet

ion tail

thin stream of ionized gas that is pushed away from the head of a comet by the solar wind; it extends directly away from the Sun; often referred to as a plasma tail

plutoid

a dwarf planet orbiting beyond Neptune

dwarf planet

a body that orbits the Sun and is massive enough that its own gravity has caused its shape to be approximately spherical, but which is insufficiently massive to have cleared other bodies from "the neighborhood" of its orbit

meteor

bright streak in the sky, often referred to as a "shooting star," resulting from a small piece of interplanetary debris entering Earth's atmosphere and heating air molecules, which emit light as they return to their ground states

meteoroid

chunk of interplanetary debris prior to encountering Earth's atmosphere

tail

component of a comet that consists of material streaming away from the main body, sometimes spanning hundreds of millions of kilometers; may be composed of dust or ionized gases

meteor shower

event during which many meteors can be seen each hour, caused by the yearly passage of Earth through the debris spread along the orbit of a comet

Kirkwood gaps

gaps in the spacing of orbital semimajor axes of asteroids in the asteroid belt, produced by dynamical resonances with nearby planets, especially Jupiter