Outburst of Comet 17P/Holmes Observed With The Solar Mass Ejection Imager

TL;DR

This study uses the Solar Mass Ejection Imager to analyze the 2007 outburst of comet 17P/Holmes, providing detailed brightness measurements, mass loss rates, and insights into the outburst mechanism.

Contribution

First time complete time-resolved brightness data of 17P/Holmes outburst from space-based observations, linking outburst dynamics to heat conduction and ice crystallization.

Findings

Brightness rise well-described by Gaussian function

Maximum mass loss rate of 3x10^5 kg/s

Ejected mass up to 10% of nucleus mass

Abstract

We present time-resolved photometric observations of Jupiter family comet 17P/Holmes during its dramatic outburst of 2007. The observations, from the orbiting Solar Mass Ejection Imager (SMEI), provide the most complete measure of the whole-coma brightness, free from the effects of instrumental saturation and with a time-resolution well-matched to the rapid brightening of the comet. The lightcurve is divided into two distinct parts. A rapid rise between the first SMEI observation on UT 2007 October 24 06h 37m (mid-integration) and UT 2007 October 25, is followed by a slow decline until the last SMEI observation on UT 2008 April 6 22h 16m (mid-integration). We find that the rate of change of the brightness is reasonably well-described by a Gaussian function having a central time of UT 2007 October 24.54+/-0.01 and a full-width-at-half-maximum 0.44+/-0.02 days. The maximum rate of brightening occurs some 1.2 days after the onset of activity. At the peak the scattering cross-section grows at 1070+/-40 km^2/s while the (model-dependent) mass loss rates inferred from the lightcurve reach a maximum at 3+/-10^5 kg/s. The integrated mass in the coma lies in the range (2 to 90)x10^10 kg, corresponding to 0.2% to 10% of the nucleus mass, while the kinetic energy of the ejecta is (0.6 to 30) MTonnes TNT. The particulate coma mass could be contained within a shell on the nucleus of thickness ~1.5 to 60 m. This is comparable to the distance traveled by conducted heat in the century since the previous outburst of 17P/Holmes. This coincidence is consistent with, but does not prove, the idea that the outburst was triggered by the action of conducted heat, possibly through the crystallization of buried amorphous ice.