FUV Observations of the Inner Coma of 46P/Wirtanen

TL;DR

This study uses Hubble Space Telescope ultraviolet observations of comet 46P/Wirtanen's inner coma to analyze atomic emissions, revealing complex composition and distribution patterns that challenge existing models.

Contribution

It provides rare, high-resolution UV spectral data of a comet's inner coma, offering new insights into its composition and emission processes beyond previous remote sensing capabilities.

Findings

Water is the main source of atomic H and O emissions.

An abundance of atomic sulfur was detected, inconsistent with common sulfur parent molecules.

Density distribution does not fit standard coma models.

Abstract

Far ultraviolet observations of comets yield information about the energetic processes that dissociate the sublimated gases from their primitive surfaces. Understanding which emission processes are dominant, their effects on the observed cometary spectrum, and how to properly invert the spectrum back to composition of the presumably pristine surface ices of a comet nuclei are all critical components for proper interpretation and analysis of comets. The close approach of comet 46P/Wirtanen in 2018-2019 provided a unique opportunity to study the inner most parts of a cometary coma with the Hubble Space Telescope Cosmic Origins Spectrograph, rarely accessible with remote observations, at length scales (100's of km) and wavelengths (900-1430 Angstroms) previously probed only by the European Space Agency's Rosetta spacecraft. Our observations show a complex picture for the inner coma; atomic production rates for H and O that show water is the dominant source of both, an abundance of atomic sulfur that is difficult to explain with the lifetimes of common sulfur parent molecules, and a density distribution that is poorly fit with both Haser and vectorial models.