On relative velocity in very young asteroid families

Abstract

Asteroid families are groups of minor planets that have a common origin in catastrophic breakup events. The very young compact asteroid clusters are a natural laboratory in which to study impact processes and the dynamics of asteroid orbits.In the first part of the paper, we define the term very young asteroid families (VYF), that is to say, younger than 1.6 Myrs, and explain why we have defined this group as being separate from young families (younger than 100 Myr), due to specific characteristics, in particularly, non-gravitational forces which have a very small effect (which could be negligible) on their dynamics and the role of the initial conditions in VYFs as being more significant. Due to these facts, the way we study VYFs may be different relative to young families.For the most part, the calculation of VYFs’ normal component of relative velocity using backward numerical integration, exhibited a clear, deep minimum, which was close to the breakup epoch. The age estimations found while employing this method were in excellent agreement with the established age estimations used by other authors. We confirmed our results with the established age estimation of the Hobson family (365 ± 67 kyrs). Concerning the Emilkowalsky family, we confirmed the results of Nesvorný and Vokrouhlický (2006) (220 ± 30 kyrs), obtaining a far clearer result using the relative velocity method rather than single-orbital element convergence. The case of the Datura family is more complex to study, mainly due to its 9:16 resonance with Mars.We have exemplified that the z-component of relative velocity may prove to be a powerful and useful criterion for VYF age estimations. The studied value of relative velocity may contain information about the ejection velocity.As an additional outcome of this paper, we have introduced two new members of two different VYFs; one new member of the Emilkowalsky family and one of the Hobson family.