The Lingering Death of Periodic Near-Sun Comet 323P/SOHO

TL;DR

This study presents detailed observations of near-Sun comet 323P/SOHO, revealing its disintegration, rapid rotation, and high likelihood of colliding with the Sun within two millennia, providing new insights into its physical properties and evolution.

Contribution

First comprehensive ground and space-based observations of 323P/SOHO, uncovering its disintegration, rapid rotation, and high collision probability with the Sun, advancing understanding of near-Sun comet behavior.

Findings

Comet developed a long tail post-perihelion indicating disintegration.

Nucleus has the shortest known rotation period of 0.522 hr.

High nongravitational effects suggest a strong likelihood of Sun collision within 2000 years.

Abstract

We observed near-Sun comet 323P/SOHO for the first time using ground and space telescopes. In late December 2020, the object was recovered at Subaru showing no cometary features on its way to perihelion. However, in our postperihelion observations it developed a long narrow tail mimicking a disintegrated comet. The ejecta, comprised of at least mm-sized dust with power-law size distribution index $3.2 \pm 0.2$, was impulsively produced shortly after the perihelion passage, during which $\gtrsim$0.1-10% of the nucleus mass was shed due to excessive thermal stress and rotational disruption. Two fragments of $\sim$20 m in radius (assuming a geometric albedo of 0.15) were seen in HST observations from early March 2021. The nucleus, with an effective radius of $86 \pm 3$ m (the same albedo assumed) and an aspect ratio of $\sim$0.7, has a rotation period of 0.522 hr, which is the shortest for known comets in the solar system and implies cohesive strength $\gtrsim$10-100 Pa in the interior. The colour of the object was freakish, and how it changed temporally has never been previously observed. Using our astrometry, we found a strong nongravitational effect following a heliocentric dependency of $r_{\rm H}^{-8.5}$ in the transverse motion of the object. Our N-body integration reveals that 323P has a likelihood of 99.7% to collide with the Sun in the next two millennia driven by the $\nu_6$ secular resonance.