Ground-based detection of a cloud of methanol from Enceladus: when is a biomarker not a biomarker?

E. Drabek-Maunder*, J. Greaves, H. J. Fraser, D. L. Clements, L. N. Alconcel

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Citations (Scopus)

Abstract

Saturn's moon Enceladus has vents emerging from a sub-surface ocean, offering unique probes into the liquid environment. These vents drain into the larger neutral torus in orbit around Saturn. We present a methanol (CH3OH) detection observed with IRAM 30-m from 2008 along the line-of-sight through Saturn's E-ring. Additionally, we also present supporting observations from the Herschel public archive of water (ortho-H2O; 1669.9 GHz) from 2012 at a similar elongation and line-of-sight. The CH3OH 5(1,1)-4(1,1) transition was detected at 5.9σ confidence. The line has 0.43 km s−1 width and is offset by +8.1 km s−1 in the moon's reference frame. Radiative transfer models allow for gas cloud dimensions from 1750 km up to the telescope beam diameter ~73 000 km. Taking into account the CH3OH lifetime against solar photodissociation and the redshifted line velocity, there are two possible explanations for the CH3OH emission: methanol is primarily a secondary product of chemical interactions within the neutral torus that: (1) spreads outward throughout the E-ring or (2) originates from a compact, confined gas cloud lagging Enceladus by several km s−1. We find either scenario to be consistent with significant redshifted H2O emission (4σ) measured from the Herschel public archive. The measured CH3OH:H2O abundance (>0.5%) significantly exceeds the observed abundance in the direct vicinity of the vents (~0.01%), suggesting CH3OH is likely chemically processed within the gas cloud with methane (CH4) as its parent species.

Original languageEnglish
Pages (from-to)1-8
Number of pages8
JournalInternational Journal of Astrobiology
DOIs
Publication statusAccepted/In press - 17 Dec 2017

Bibliographical note

Publisher Copyright:
Copyright © Cambridge University Press 2017

Keywords

  • Astrobiology
  • astrochemistry
  • planets and satellites: Enceladus
  • submillimeter:general

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Physics and Astronomy (miscellaneous)
  • Space and Planetary Science
  • Earth and Planetary Sciences (miscellaneous)

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