Details of Recent Collisions of Asteroids 832 Karin and 158 Koronis
Abstract
We present analysis of the membership and dynamics of two recently formed asteroid clusters: 832 Karin (5.72 My) and 158 Koronis (15.0 My). The unprecedented detail of both collisions (one catastrophic and one not) provides rigorous tests of asteroid collision models.
We use the AstDyS catalog of analytic proper elements to identify asteroids with high quality orbits that are dynamically near the Karin cluster (873 objects), and use the OrbFit software to compute precise synthetic proper elements. We define a cut in five dimensional phase space to determine Karin membership. The key to an effective cut is the use of two linear combinations of elements: a combination of the longitudes that is independent of the Yarkovsky drift and a combination of eccentricity and driftcorrected semimajor axis.
Karin cluster membership is increased to 387 objects, four times the previously published number. Highlights of analysis include a sizefrequency distribution with significant curvature, and two clusters in the histogram of spin obliquities (inferred from the Yarkovsky drift of the longitudes). The latter is consistent with capture of the smallest members (diameters less than 2 km) in Slivan states.
Removal of the Karin members from the sample reveals a previously unknown cluster of 151 objects resulting from a recent noncatastrophic collision with Koronis (which has 98.7% of the total mass). With an age of 15 My, individual longitudes have drifted by as much as 540 degrees due to the Yarkovsky effect, yet it remains possible to unwrap the angles and determine membership. Highlights of the analysis include final speeds relative to Koronis less than the escape speed and a pronounced preference for outflow directions in a small cone. The mass of the material launched below escape speed likely exceeds that of the escaped objects.
Funded by a Kuiper endowment and a Calvin Research Fellowship.
 Publication:

AAS/Division for Planetary Sciences Meeting Abstracts #41
 Pub Date:
 September 2009
 Bibcode:
 2009DPS....41.2705M