A significant area of exobiological research is the investigation of a
special class of stony meteorites known as "carbonaceous chondrites." It
is increasingly apparent that almost all life-detection concepts rely on
the eventual analysis of the solid materials that may be available on
Mars and other planetary surfaces. Cosmic dust and meteorites are two
classes of material bodies that reach the Earth from outer space. The
carbonaceous chondrites are the only extraterrestrial materials known to
contain organic carbon.
The study of meteorites has generated an astonishing diversity of
hypotheses. There is agreement at only one point: that meteorites are
preserved chunks of very ancient, perhaps primordial, planetary matter
and that when we are able to understand the curious structures and
chemical and isotopic variations in the meteorites, we will also know a
great deal about early planetary (and perhaps preplanetary) history.
Meteorites provide a more representative sample of average planetary
matter than the highly differentiated crust of the Earth. Although it is
known that the meteorite parent bodies ceased to be geochemically active
shortly after their formation, some 4½ billion years ago, there is no
consensus on the nature of the meteorite parent bodies, not even on such
basic properties as size, location, and multiplicity. This is not
surprising because the meteorite samples commonly available for study
represent only about 10⁻²³ to 10⁻²⁶ of the parent body.