Comet C/2017 S3 (PanSTARRS): Outbursts and Disintegration

TL;DR

This paper studies the disintegration of comet C/2017 S3 (PanSTARRS) through hydrogen Lyman-alpha observations, analyzing outbursts, water production, and particle size distribution to understand its final breakup near perihelion.

Contribution

It provides the first estimates of the nucleus size and particle distribution during disintegration based on SWAN observations of the comet's water production.

Findings

Detected a small outburst at 1.1 AU and a larger one at 0.8 AU.

Estimated the nucleus size before disintegration using water production data.

Analyzed the size distribution of particles as the comet faded.

Abstract

The Solar Wind ANisotropies (SWAN) all-sky hydrogen Lyman-alpha camera on the SOlar and Heliospheric Observer (SOHO) satellite observed the hydrogen coma of comet C/2017 S3 (PanSTARRS) for the last month of its activity from 2018 July 4 to August 4 and what appears to have been its final disintegration just 11 days before its perihelion on August 15. The hydrogen coma indicated water production had a small outburst on July 8 at a heliocentric distance of 1.1AU and then a much larger one on July 20 at 0.8 AU. Over the following two weeks the water production dropped by more than a factor of ten after which it was no longer detectable. The behavior is reminiscent of comet C/1999 S4 (LINEAR) in 2000, which had a few small outbursts on its inbound orbit and a major outburst at a heliocentric distance of about 0.8 AU, which was close to its perihelion, followed by its complete disintegration that was documented by several sets of observations including SWAN. C/2017 S3 (PanSTARRS) however had a much larger water production rate than C/ 1999 S4 (LINEAR). Here we estimate the size of the nucleus of C/2017 S3 just before its final outburst and apparent disintegration was estimated using the total amount of water produced during its last weeks for a range of values of the refractory/ice ratio in the nucleus. We also determine the size distribution of the disintegrating particles as the comet faded.