Asteroids

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Resources: аImagesImpact: Earth

Terminology:аmeteor, meteoroid, meteorite, impactor

Tutorials: аnone

Background

Asteroids are rocky or metallic bodies that orbit the Sun and are generally smaller than most moons. аThey are found throughout the Solar System, with a higher concentration between the orbits of Mars and Jupiter, and a likely much larger number past the orbit of Neptune. These objects are most likely remnants from the formation of the Solar System that were not absorbed by the large planets as they formed. Thus, a better term for these objects as a whole is "minor planets", while "asteroids" has come to refer specifically to the objects orbiting between Mars and Jupiter.

The physical composition of asteroids is varied and in most cases poorly understood. Ceres appears to be composed of a rocky core covered by an icy mantle, where Vesta is thought to have a nickel-iron core, olivine mantle, and basaltic crust. 10 Hygiea, however, which appears to have a uniformly primitive composition of carbonaceous chondrite, is thought to be the largest undifferentiated asteroid. Most of the smaller asteroids are thought to be piles of rubble held together loosely by gravity, though the largest are probably solid. Some asteroids have moons or are co-orbiting binaries: Rubble piles, moons, binaries, and scattered asteroid families are believed to be the results of collisions that disrupted a parent asteroid.

Albedoаis a measure of the percentage of light that an object reflects. Specifically, theаgeometric albedoаis a measure of the reflectivity of an object when the source of light is directly behind the observer - like when viewing an asteroid at opposition. Albedo is measured on a scale of zero to one, zero representing a surface that reflects no light, and one representing an object that reflects all incoming light.аAsteroids typically have very low albedos, and many cannot be seen without the use of binoculars or a telescope.

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