Asteroid
An asteroid is a rocky, airless remnant left over from the early formation of the Solar System about 4.6 billion years ago. Most asteroids in our Solar System are found in the Main Asteroid Belt, a region between the orbits of Mars and Jupiter. They range in size from Ceres (about 940 km in diameter, classified as a dwarf planet) to bodies less than 1 metre across, and are composed primarily of rock, metal, and carbon compounds.
Classification of Asteroids by Composition
| Type | Composition | Location | Percentage of Belt |
|---|---|---|---|
| C-type (Carbonaceous) | Carbon-rich, dark | Outer Belt | ~75% |
| S-type (Silicaceous) | Silicate and metal | Inner Belt | ~17% |
| M-type (Metallic) | Iron and nickel | Middle Belt | ~8% |
| V-type (Vestoids) | Volcanic basalt | Near Vesta | Rare |
| NEA (Near-Earth) | Various | Near Earth orbit | Special group |
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Related Terms
Solar System
The Solar System is the gravitationally bound system comprising the Sun and all the objects that orbit it, including eight planets, their moons, dwarf planets, asteroids, comets, and interplanetary dust. It formed approximately 4.6 billion years ago from the gravitational collapse of a giant molecular cloud. The Solar System extends from the Sun to the Oort Cloud, spanning distances of up to 100,000 astronomical units.
Comet
A comet is an icy small Solar System body that, when passing close to the Sun, warms up and begins to release gases and dust in a process called outgassing, producing a visible atmosphere (coma) and sometimes a bright tail that can extend millions of kilometres into space. Comets originate from two main regions: the Kuiper Belt (short-period comets) and the Oort Cloud (long-period comets). They are time capsules from the early Solar System, composed of frozen water, carbon dioxide, methane, and dust.
Meteor
A meteor is the visible streak of light produced when a meteoroid — a small rocky or metallic body in outer space — enters Earth's atmosphere at high speed and burns up due to friction with air molecules. Commonly called a "shooting star" or "falling star", a meteor is the luminous phenomenon itself, not the physical object. If a meteoroid survives its passage through the atmosphere and lands on the surface, it is then called a meteorite.
From Greek "asteroeides" (star-like), coined by astronomer William Herschel in 1802 from "aster" (star) + "-oeides" (having the form of). The name was given because asteroids appeared as points of light (like stars) through early telescopes, unlike planets which showed discs.