Molecular composition of comet 46P/Wirtanen from millimetre-wave spectroscopy

TL;DR

This study provides a detailed molecular composition of comet 46P/Wirtanen using millimetre-wave spectroscopy, identifying several molecules including complex organics and establishing their relative abundances.

Contribution

First detection of some molecules in a Jupiter-family comet and comprehensive molecular survey using IRAM 30-m and NOEMA telescopes.

Findings

Identified 11 molecules, including complex organics.

Measured gas outflow velocity and temperature accurately.

Found the comet to be rich in methanol but depleted in certain other molecules.

Abstract

We present the results of a molecular survey of comet 46P/Wirtanen undertaken with the IRAM 30-m and NOEMA radio telescopes in December 2018. Observations at IRAM 30-m during the 12-18 Dec. period comprise a 2 mm spectral survey covering 25 GHz and a 1 mm survey covering 62 GHz. The gas outflow velocity and kinetic temperature have been accurately constrained by the observations. We derive abundances of 11 molecules, some being identified remotely for the first time in a Jupiter-family comet, including complex organic molecules such as formamide, ethylene glycol, acetaldehyde, or ethanol. Sensitive upper limits on the abundances of 24 other molecules are obtained. The comet is found to be relatively rich in methanol (3.4 percent relative to water), but relatively depleted in CO, CS, HNC, HNCO, and HCOOH.