Hubble Space Telescope Observations of Active Asteroid P/2020 O1 (Lemmon-PANSTARRS)

TL;DR

This study uses Hubble observations to analyze the activity of asteroid P/2020 O1, suggesting sublimation of near-surface ice as the cause of its mass loss and rapid rotation, indicating it is a main-belt comet.

Contribution

First detailed Hubble study linking sublimation-driven activity to an asteroid with rapid rotation and small size, expanding understanding of ice distribution in the asteroid belt.

Findings

Mass loss peaks at ~1 kg/s and declines over four months.

Evidence suggests rapid rotation with a period less than 2 hours.

Ejection velocities of particles are near the escape speed, supporting sublimation-driven activity.

Abstract

We present Hubble Space Telescope observations of active asteroid P/2020 O1 taken to examine its development for a year after perihelion. We find that the mass loss peaks <~1 kg/s in 2020 August and then declines to nearly zero over four months. Long-duration mass loss (~180 days) is consistent with a sublimation origin, indicating that this object is likely an ice-bearing main-belt comet. Equilibrium sublimation of water ice from an area as small as 1580 m^2 can supply the observed mass loss. Time-series photometry shows tentative evidence for extremely rapid rotation (double-peaked period < 2 hr) of the small nucleus (effective radius ~420 m). Ejection velocities of 0.1 mm particles are comparable to the 0.3 m/s gravitational escape speed from the nucleus, while larger particles are ejected at speeds less than the escape velocity. These properties are consistent with the sublimation of near-surface ice aided by centripetal acceleration. If water ice sublimation is confirmed, P/2020 O1 would be the icy asteroid with the smallest semimajor axis (highest temperature), setting new bounds on the distribution of ice in the asteroid belt.