Descriptive Astronomy 101
Asteroids and Meteoroids


Rocks in Space

Asteroids - large rocky or metallic bodies generally greater than a few meters in diameter
Meteoroid - small rocky or metallic bodies generally less than a few meters diameter to microscopic in size
Meteor - a meteoroid that is passing through a planetary atmosphere.
Meteorite - a meteoroid that has survived passage through the atmosphere and impacted on the surface. (Falls and Finds)

Asteroids

More than 150,000 asteroids have been identified
Largest: Ceres, 1000 km diameter
If all asteroids were gathered together, they would form a body only 2000 km in diameter.
Asteroids and meteoroids are the left over debris from the accretion process which formed the planets.
Asteroids originally formed throughout the solar nebula with a uniform distribution.

Asteroid Belt

Within 100 million years almost all asteroids were cleaned out of the inner Solar System.
Most of the remaining asteroids are now found in a zone between Mars and Jupiter

Trojan Asteroids:
Amor Asteroids:
Apollo Asteroids:
Aten Asteroids:

Types of Asteroids

Classification of asteroids is primarily based on the reflectance spectrum and albedo.
14 different classes have been proposed: A, B, C, D, E, F, G, M, P, Q, R, S, T, V
C-class asteroid: very dark and non-reflective asteroid, gray in color, with a composition believed to be similar to that of carbonaceous chondrites
M-class asteroid: relatively bright and reflective asteroid, made mainly of metallic iron and nickel
S-class asteroid: moderately bright, slightly reddish type of asteroid believed to be composed largely of silicate minerals

Primitive Asteroids

Unaltered remnants of the accretion process.
They are large planetesimals that accreted in the solar nebula - unchanged since formation

Processed Asteroids

Compositions that are similar to the cores, mantles, or crusts of the terrestrial worlds.
Fragments of larger asteroids that underwent differentiation - planetary processes
The interior melted so that metals sank to the center and rocks rose to the surface.
Meteoroids are produced by impact collisions.

Meteorites

3 Classes
Stony
Iron
Stony-Iron

Stony Meteorites

Chondrites
Contain chondrules
3 Types:
Ordinary Chondrites
Enstatite Chondrites - enstatite-rich
Carbonaceous Chondrites - contain carbon and organic molecules (including amino acids)
- most primitive meteorites
- form at greater than 3 AU

Achondrites - stony meteorites without chondrules
Formed closer than 3 AU
Formed as the result of planetary processes - melting and crystallization - in a very large asteroid large
12 types - Acapulcoits, Angrite, Aubrites, Brachinite, Diogenites, Eucrites, Howardites, Lodranite, Lunar, SNC, Ureilites, Winonaite

Stony-Iron Meteorites

Combination of stony and iron materials
Pallasites
Formed when core material mixed with silicate magma
Mesosiderites

Iron Meteorites

Composed of iron and nickel
Formed as the core of a planetary body
Widmanstatten Pattern

Tektites

Silica-rich impact generated glass objects