Hubble Space Telescope Observations of Main Belt Comet (596) Scheila

TL;DR

Hubble observations of (596) Scheila during its dust outburst reveal a coma and dust ejection likely caused by an impact event, providing insights into main belt comet activity.

Contribution

This study presents detailed Hubble data on Scheila's dust outburst, suggesting impact as the cause, which is a novel explanation for such activity in main belt comets.

Findings

Coma with scattering cross-section ~2.2x10^4 km^2 observed.

Dust particles deflected by solar radiation pressure on ~2x10^4 km scale.

Mass loss inconsistent with rotational instability or electrostatic ejection.

Abstract

We present Hubble Space Telescope Observations of (596) Scheila during its recent dust outburst. The nucleus remained point-like with absolute magnitude V(1,1,0) = 8.85+/-0.02 in our data, equal to the pre-outburst value, with no secondary fragments of diameter =>100 m (for assumed albedos 0.04). We find a coma having a peak scattering cross-section ~2.2x10^4 km^2 corresponding to a mass in micron-sized particles of ~4x10^7 kg. The particles are deflected by solar radiation pressure on projected spatial scales ~2x10^4 km, in the sunward direction, and swept from the vicinity of the nucleus on timescales of weeks. The coma fades by ~30% between observations on UT 2010 December 27 and 2011 January 04. The observed mass loss is inconsistent with an origin either by rotational instability of the nucleus or by electrostatic ejection of regolith charged by sunlight. Dust ejection could be caused by the sudden but unexplained exposure of buried ice. However, the data are most simply explained by the impact, at ~5 km/s of a previously unknown asteroid ~35 m in diameter.