The young Adelaide family: Possible sibling to Datura?

Abstract

Very young asteroid families may record processes that accompanied their formation in the most pristine way. This makes analysis of this special class particularly interesting. We studied the very young Adelaide family in the inner part of the main belt. This cluster is extremely close to the previously known Datura family in the space of proper orbital elements and their ages overlap. As a result, we investigated the possibility of a causal relationship between the two families. We identified Adelaide family members in the up-to-date catalogue of asteroids. By computing their proper orbital elements we inferred the family structure. Backward orbital integration of selected members allowed us to determine the age of the family. The largest fragment (525) Adelaide, an S-type asteroid about $10$ km in size, is accompanied by 50 sub-kilometre fragments. This family is a typical example of a cratering event. The very tiny extent in the semi-major axis minimises chances that some significant mean motion resonances influence the dynamics of its members, though we recognise that part of the Adelaide family is affected by weak, three-body resonances. Weak chaos is also produced by distant encounters with Mars. Simultaneous convergence of longitude of node for the orbits of six selected members to that of (525) Adelaide constrains the Adelaide family age to $536\pm 12$ kyr (formal solution). While suspiciously overlapping with the age of the Datura family, we find it unlikely that the formation events of the two families are causally linked. In all likelihood, the similarity of their ages is just a coincidence.