Rocks – Classes

• orbit the Sun inside Earth’s orbit, crossing our planet’s orbit no less than once per year.
• Daily List Of Aten Minor Planets (by designation)
• Plot of the Innermost Solar System

• cross Earth’s orbit with a period greater than one year.

• Mars crossing rocks. For example, Eros, see Mission NEAR Shoemaker, human’s first machine to orbit an asteroid.

• orbit the sun ~ 5.1-5.2 AU.

• orbit the Sun between Jupiter and Neptune, typically 5 to 30 astronomical units (AU) away.
• orbits are very elliptical and cross the orbits of Jupiter and Neptune
• related to Comets but never produce a coma and tail
• Plot of the Inner Solar System

• orbit the sun at a distance of at least 38 AU

Rare, (est. only 5%) characterized by the presence of two nickel-iron alloy metals: kamacite and taenite, combined with minor amounts of non-metallic phases and sulfide minerals, form three basic subdivisions of irons. Depending upon the percentage of nickel to iron, these subdivisions are classified as:
     hexahedrites (4-6% Ni)
     octahedrites (6-12% Ni)
     ataxites (12+% Ni)
Octahedrites, which are the most common type of iron meteorite, exhibit a unique structural feature called the Widmanstatten pattern when etched with a weak acid. This unique crystal pattern is the result of the combination of the two nickel-iron minerals
kamacite and taenite being present in approximately equal amounts.

Consist of almost equal amounts of nickel-iron alloy and silicate minerals. Although all stony-irons may not be genetically related or have similar composition, they are combined into one group and divided into two subgroups for convenient classification. The Pallasite group is characterized by olivine crystals surrounded by a nickel-iron structure which forms a continuous enclosing network around the silicate portion. Mesosiderites, on the other hand, consist mainly of plagioclase and pyroxene silicates in the form of heterogeneous aggregates intermixed with the metal alloy. No distinct separation between the metal and silicate phases is readily apparent as it is with the Pallasites.

The most abundant of the three meteorite groups and come closest to resembling earth rocks in their appearance and composition. The major portion of these meteorites consists of the silicate minerals olivine, pyroxene, and plagioclase feldspars. Metallic nickel-iron occurs in varying percentages and is accompanied by an iron-sulfide mineral. Aside from
being the most abundant meteorite type, stony meteorites have the greatest variety in composition, color, and structure. One particular structural feature called chondrules divides the group into two main subgroups:
     Chrondrites, those with chondrules
     Achondrites, those without chondrules
Many scientists believe that these small, rounded, nearly spherical chondrules may represent the most primitive material in the solar system.