# Fragmented Comet 73P/Schwassmann-Wachmann 3

## TL;DR

This study analyzes archival Hubble data of comet 73P/Schwassmann-Wachmann 3 to investigate its fragmentation, finding a rotation period too long for rotational breakup and suggesting other mechanisms caused its fragmentation.

## Contribution

The paper provides the first detailed analysis of the primary fragment using archival Hubble data, constraining the rotation period and physical properties to better understand fragmentation causes.

## Key findings

- Rotation period is 10.38 hours, longer than the critical period for rotational instability.
- Detected cyclic photometric variations indicating rotational modulation of mass loss.
- Estimated nucleus radius is approximately 0.4 km.

## Abstract

Comet 73P/Schwassmann-Wachmann 3 has been observed to fragment on several occasions, yet the cause of its fragmentation remains poorly understood. We use previously unpublished archival Hubble Space Telescope data taken in 2006 to study the properties of the primary fragment, 73P-C, in order to constrain the potential fragmentation mechanisms. Currently the literature presents a wide range of measured rotational periods, some of which suggest that the nucleus might have split due to rotational instability. However, we find the most likely value of the rotation period to be 10.38 $\pm$ 0.04 hours (20.76 $\pm$ 0.08 hours if double-peaked), much longer than the critical period for rotational instability for any reasonable nucleus density and shape, even in the absence of tensile strength. We also find strong, cyclic photometric variations of about 0.31 $\pm$ 0.01 magnitudes in the central light from this object, while similar variations with a smaller range are apparent in the surrounding dust coma. These observations are compatible with rotational modulation of the mass loss rate and with dust having a mean outflow speed of $107 \pm 9$ m s$^{-1}$. Finally, we also estimate the radius of the nucleus to be 0.4 $\pm$ 0.1 km accounting for dust contamination and assuming a geometric albedo of 0.04.