Main-Belt Comet 238P/Read Revisited

TL;DR

This study documents the recurrent activity of main-belt comet 238P/Read, confirming it as a true sublimation-driven comet through detailed observations of its activity cycle and physical properties.

Contribution

It provides the first detailed analysis of 238P's activity recurrence, supporting the sublimation-driven nature of main-belt comets.

Findings

238P's nucleus radius is approximately 0.4 km.

Activity increases observed from September 2010, reaching levels similar to 2005.

238P is confirmed as a sublimation-driven comet with recurrent activity.

Abstract

We present a series of observations of the return of activity in main-belt comet 238P/Read. Using data obtained in July and August 2010 when 238P appeared to be largely inactive, we find best-fit IAU phase function parameters of H=19.05+/-0.05 mag, corresponding to a nucleus radius of r_n ~ 0.4 km (assuming an albedo of p_R=0.05), and G=-0.03+/-0.05. Observations from September 2010 onward show a clear rise in activity, causing both a notable change in visible morphology and increasing photometric excesses beyond what would be expected based on bare nucleus observations. By the end of the observing period reported on here, the dust mass in the coma shows indications of reaching a level comparable to that observed in 2005, but further observations are highly encouraged once 238P again becomes observable from Earth in mid-2011 to confirm whether this level of activity is achieved, or if a notable decrease in activity strength compared to 2005 can be detected. Comet 238P is now the second main-belt comet (after 133P/Elst-Pizarro) observed to exhibit recurrent activity, providing strong corroboration for the conclusion that it is a true comet whose active episodes are driven by sublimation of volatile ice.