Dynamics of Large Fragments in the Tail of Active Asteroid P/2010 A2

TL;DR

This study tracks large fragments from active asteroid P/2010 A2's tail, revealing their ejection velocities and directions, which suggest the asteroid's breakup was likely due to rotational instability.

Contribution

It provides detailed measurements of fragment velocities and trajectories, supporting the hypothesis of rotational break-up as the cause of the asteroid's disruption.

Findings

Fragments ejected at velocities near the escape speed.

Ejection directions are opposite to the asteroid's motion.

Ejection velocities lie in a plane including the nucleus.

Abstract

We examine the motions of large fragments at the head of the dust tail of active asteroid P/2010 A2. In previous work we showed that these fragments were ejected from the primary nucleus in early 2009, either following a hypervelocity impact or by rotationally induced break-up. Here, we follow their positions through a series of Hubble Space Telescope images taken during the first half of 2010. The orbital evolution of each fragment allows us to constrain its velocity relative to the main nucleus after leaving its sphere of gravitational influence. We find that the fragments constituting a prominent X-shaped tail feature were emitted in a direction opposite to the motion of the asteroid and towards the south of its orbital plane. Derived emission velocities of these primary fragments range between 0.02 and 0.3 m/s, comparable to the ~0.08 m/s gravitational escape speed from the nucleus. Their sizes are on the order of decimeters or larger. We obtain the best fits to our data with ejection velocity vectors lying in a plane that includes the nucleus. This may suggest that the cause of the disruption of P/2010 A2 is rotational break-up.