THE PROGRESSIVE FRAGMENTATION OF 332P/IKEYA–MURAKAMI

Abstract

We describe 2016 January–April observations of the fragments of 332P/Ikeya–Murakami, a comet earlier observed in a 2010 October outburst. We present photometry of the fragments and perform simulations to infer the time of breakup. We argue that the eastern-most rapidly brightening fragment ( F 4) best corresponds to the original nucleus, rather than the initial bright fragment F 1. We compute radial and tangential nongravitational parameters, A 1  = (1.5 ± 0.4) × 10 −8 au day −2 and (7.2 ± 1.9) × 10 −9 au day −2 ; both are consistent with zero at the 4 σ level. Monte Carlo simulations indicate that the fragments were emitted on the outbound journey well after the 2010 outburst, with bright fragment F 1 splitting in early 2014 and the fainter fragments within months of the 2016 January recovery. Western fragment F 7 is the oldest, dating from 2011. We suggest that the delayed onset of the splitting is consistent with a self-propagating crystallization of water ice.