On the age of the Beagle secundary asteroid family

Abstract

The Beagle family is a C-type subgroup of the Themis family, in the outer main belt. Previous works suggested that it could be younger than 20 Myr and a possible source for the dust in the i≃1.4∘ α zodiacal dust band. Here we took advantage of a much larger database for Beagle family members to revisit previous age estimates of this group. Standard dating techniques based on the family V-shape or on Monte Carlo methods of Yarkovsky and YORP mobility suggest that i) there might be a dichotomy for the inner and outer part of the Beagle family, which may be either two separate families or the product of an anisotropic ejection velocity field and that ii) the age of the possibly younger outer part of the Beagle family should be 35−35 +65 Myr. The past convergence of Beagle longitude of the node is compatible with a family age of ≃14 Myr, when (1678) Glarona is used as a reference orbit. Without further information on Beagle members spin states, however, only very lower limits on the family age can be currently obtained when the Yarkovksy force is accounted for.