RECENT PROGRESS ON GENETIC TESTING OF ASTEROID DYNAMICAL GROUPS

In this paper we will discuss recent progress on constraining genetic relationships between asteroids in dynamical clusters or families. The presence and nature of collisionally-produced asteroid families provide important constraints on the processes involved in the disruptions of large (~100-1000 km diameter) planetesimals, on the collisional lifetime of asteroids as a function of size and composition, on the thermal history and internal compositional structure of their parent bodies, and on the rate of orbital diffusion in the asteroid belt.

A dynamical asteroid family is a group of asteroids that follow similar orbits about the Sun. There are disagreements on both the total number of dynamical families and their memberships. In addition, physical studies of asteroids and meteorites suggest that there is a problem with both the number of families identified to date and the inferred homogeneity within these families.

A genetic asteroid family is one in which the members were derived from a common parent body. Genetic families provide glimpses of the interiors of small planetary objects whose compositions, thermal evolutions, and geochemical processes were established by the ambient conditions present during the formation epoch of the solar system. Thus asteroids provide the only in situ record from the earliest part of solar system history for the mainbelt region.

The most reliable way of testing the reality of asteroid families is by deriving the mineralogy of individual members by remote sensing techniques. However, significant progress can be made by using meteorites as validity checks on asteroid compositional interpretations derived from remote sensing data. That is a primary goal of the Family Asteroid Compositional Evaluation Survey, which was established to fill gaps in existing family asteroid spectroscopic databases and to obtain new data on additional family members.

In order to accurately derive the mineralogy of asteroid from ground-based, remotely-sensed data, it is essential to remove atmospheric contamination effects from the spectra as completely as possible. This is particularly important with respect to near-infrared data (~7.2-2.5 microns) because absorption features due to atmospheric water vapor occur in mineralogically critical portions of this spectral region.