In Search of Recent Disruption of (3200) Phaethon: Model Implication and Hubble Space Telescope Search

Abstract

Near-Earth asteroid (3200) Phaethon is notable for its association to a strong annual meteor shower, the Geminids, indicative of one or more episodes of mass ejection in the past. The mechanism of Phaethon's past activity is not yet understood. Here we present a Hubble Space Telescope (HST) search of meter-sized fragments in the vicinity of Phaethon, carried out during Phaethon's historic approach to the Earth in mid-December of 2017. Numerical simulation conducted to guide HST's pointing also show that the dynamical evolution of Phaethon-originated particles is quick, as ejected materials take no longer than $\sim250$ yr to spread to the entire orbit of Phaethon. Our search was completed down to 4-meter-class limit (assuming Phaethon-like albedo) and was expected to detect 0.035% particles ejected by Phaethon in the last several decades. The negative result of our search capped the total mass loss of Phaethon over the past few dozen orbits to be $10^{12}$ kg at $3\sigma$ level, taking the best estimates of size power-law from meteor observations and spacecraft data. Our result also implies a millimeter-sized dust flux of $<10^{-12} \mathrm{m^{-2} s^{-1}}$ within 0.1 au of Phaethon, suggesting that any Phaethon-bound mission is unlikely to encounter dense dust clouds.