Disintegration of Long-Period Comet C/2021 A1 (Leonard)

TL;DR

This study documents the complete disintegration of comet C/2021 A1 (Leonard), showing no surviving fragments with high-resolution imaging and attributing the breakup to rotational instability caused by outgassing torques.

Contribution

It provides detailed observational evidence of the comet's disintegration and proposes rotational instability as the primary mechanism, contrasting with other models.

Findings

No surviving fragments detected with Hubble observations.

The comet's nucleus was approximately 0.6 km in radius before disintegration.

Rotational instability is the most plausible cause of breakup.

Abstract

We present imaging observations of the disintegrating long-period comet C/2021 A1 (Leonard). High resolution observations with Hubble Space Telescope show no evidence for surviving fragments, and place a 3 sigma upper limit to their possible radius about 60 m (albedo 0.1 assumed). In contrast, wide field observations from the Swan Hill Observatory, Australia, show an extensive debris cloud, the cross-section and estimated mass of which are consistent with complete disintegration of the nucleus near mid- December 2021 (at about 0.8 au). Two methods give the pre-disruption nucleus radius, r = 0.6+/-0.2 km. Tidal, collisional, sublimation and pressure-confined explosion models provide implausible explanations of the disintegration. However, rotational instability driven by outgassing torques has a very short timescale (of order 0.1 year) given the orbit and size of the C/2021 A1 nucleus, and offers the most plausible mechanism for the disruption. Initial rotational breakup is accelerated by the exposure and strong sublimation of previously buried volatiles, leading to catastrophic destruction of the nucleus.