Drabek-Maunder, Emily  ORCID: https://orcid.org/0000-0002-3476-2260, Greaves, Jane ORCID: https://orcid.org/0000-0002-3133-413X, Fraser, Helen Jane, Clements, David and Alconcel, Leah-Nani
2019.
Ground-based detection of a cloud of methanol from Enceladus: When is a biomarker not a biomarker?
International Journal of Astrobiology
18
(1)
, pp. 25-32.
10.1017/S1473550417000428
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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 5.9 sigma confidence. The line has 0.43 km/s width and is offset by +8.1 km/s in the moon's reference frame. Radiative transfer models allow for gas cloud dimensions from 1750 km up to the telescope beam diameter ~73000 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. We find either scenario to be consistent with significant redshifted H2O emission (4 sigma) measured from the Herschel public archive. The measured CH3OH:H2O abundance (> 0.5 per cent) significantly exceeds the observed abundance in the direct vicinity of the vents (~0.01 per cent), suggesting CH3OH is likely chemically processed within the gas cloud with methane (CH4) as its parent species.
| Item Type: | Article |
|---|---|
| Date Type: | Publication |
| Status: | Published |
| Schools: | Schools > Physics and Astronomy |
| Publisher: | Cambridge University Press |
| ISSN: | 1473-5504 |
| Date of First Compliant Deposit: | 9 November 2017 |
| Date of Acceptance: | 12 October 2017 |
| Last Modified: | 29 Nov 2024 05:30 |
| URI: | https://orca.cardiff.ac.uk/id/eprint/105778 |
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