Transient Fragments in Outbursting Comet 17P/Holmes

TL;DR

This study used wide-field imaging to analyze the 2007 outburst of comet 17P/Holmes, revealing multiple active fragments likely resulting from nucleus breakup, with implications for cometary fragmentation processes.

Contribution

First detailed imaging analysis of active fragments in comet 17P/Holmes, showing they are active cometesimals and providing size estimates and activity decay rates.

Findings

Sixteen active fragments identified with sizes between 10 m and 100 m.

Fragments are active, producing their own dust comae.

Fragments fade steadily at about 0.2 mag/day.

Abstract

We present results from a wide-field imaging campaign at the Canada-France-Hawaii Telescope to study the spectacular outburst of comet 17P/Holmes in late 2007. Using image-processing techniques we probe inside the spherical dust coma and find sixteen fragments having both spatial distribution and kinematics consistent with isotropic ejection from the nucleus. Photometry of the fragments is inconsistent with scattering from monolithic, inert bodies. Instead, each detected fragment appears to be an active cometesimal producing its own dust coma. By scaling from the coma of the primary nucleus of 17P/Holmes, assumed to be 1.7 km in radius, we infer that the sixteen fragments have maximum effective radii between ~ 10 m and ~ 100 m on UT 2007 Nov. 6. The fragments subsequently fade at a common rate of ~ 0.2 mag/day, consistent with steady depletion of ices from these bodies in the heat of the Sun. Our characterization of the fragments supports the hypothesis that a large piece of material broke away from the nucleus and crumbled, expelling smaller, icy shards into the larger dust coma around the nucleus.