0 Assigned ID: 1414 ----- Attempting Submission 1 (Fri Mar 26 18:36:56 GMT 2021) ----- HST Phase I Proposal 1414 successfully submitted. Receipt: # 1414-1 ----- Attempting Submission 2 (Fri Apr 09 21:13:35 GMT 2021) ----- 331P/Gibbs (P/2012 F5) possesses one of the most detailed and best time-resolved datasets of any active asteroid, with Hubble data from 42 orbits obtained in Cycles 23, 24 and 25. These data are of high quality but remain unpublished. We propose to use these archival data to characterize 331P, with the science aim being to understand the cause of its activity. Several possible causes of mass loss in active asteroids exist, ranging from the sublimation of near surface ice, to asteroid-asteroid impact, rotational instability (driven by YORP, or by outgassing torques), thermal fracture and desiccation stresses. In 331P, both impact and rotational instability have been suggested, based on limited analyses of ground-based data. We will use the much higher resolution and better time-resolved Hubble data to test these mechanisms, while determining physical parameters including the rotation of the primary, the sizes and dust contents of the secondaries, the dust ejection speed, the time profile of the ejection and the size distribution of the ejected particles. Few active asteroids are known and fewer still have been observed in detail sufficient to determine their underlying physics. We should not miss this opportunity to examine a spectacular example of the active asteroids class. This team is experienced in using HST for the study of small bodies, with numerous refereed publications in the last decade. D. Jewitt is a ground- and space-based observer of small solar system bodies with a long record of publication in this area. J. Li brings expertise in data reduction and analysis as applied to the study of comets. Solar System Astronomy 0 Regular false false false false false SUPPORTED