Physical Properties of Main-Belt Comet P/2005 U1 (Read)

TL;DR

This study presents detailed physical observations and modeling of the main-belt comet P/2005 U1 (Read), revealing dust emission characteristics, activity timeline, and nucleus size, supporting sublimation-driven activity over impact scenarios.

Contribution

First comprehensive physical analysis of P/2005 U1 (Read), including dust emission modeling, activity timeline estimation, and nucleus size determination, highlighting sublimation as the activity mechanism.

Findings

Dust particles larger than 10 microns dominate the coma and tail.

Mass loss rate during activity was about 0.2 kg/s.

Activity likely began at least two months before discovery.

Abstract

The main-belt comets occupy dynamically asteroidal orbits in the main asteroid belt. Here we present physical observations of the second-known member of this population, P/2005 U1 (Read), which showed vigorous cometary activity from 2005 October 24 to 2005 December 27. Monte Carlo numerical simulations of P/Read's dust emission indicate that the coma and tail are optically dominated by dust particles larger than 10 microns in size with terminal ejection velocities of 0.2 to 3 m/s. We estimate P/Read's mass loss rate during this period to be approximately 0.2 kg/s, roughly an order of magnitude larger than that calculated for 133P/Elst-Pizarro. We also find that emission likely began at least two months prior to P/Read's discovery, though we note this is a lower limit and that earlier start times are possible. Optical colors measured for P/Read while it was active are approximately solar (B-V=0.63+/-0.05, V-R=0.37+/-0.04, R-I=0.39+/-0.04) but are likely to be dominated by coma particles. Observations of P/Read in 2007 when it appears largely inactive show an extremely small nucleus with an absolute magnitude of H_R~20.1+/-0.4, corresponding to an effective radius of r~0.3 km. P/Read's activity is consistent with sublimation-driven dust emission and inconsistent with dust emission due to an impact, though the unusual strength of the 2005 outburst suggests the possibility that it could have been due to the sublimation of a freshly-exposed reservoir of volatile material.