Detection of low mass amines, carbonyls and aromatics from within Enceladus - suitable precursors for biologically-relevant hydrothermal synthesis
Abstract
Enceladus' plume material - gases and ice grains - escaping through fractures in its icy shell, initially derives from a global, subsurface, salty ocean which percolates the moon's porous rocky core [1]. The detections of nanophase silica grains in the plume-sourced E ring [2], and molecular hydrogen in the plume itself [3], strongly indicate extant Enceladean hydrothermal activity and/or serpentinization reactions at the sea floor or within the core. The ocean conditions (temperatures reaching 90 °C and pH ≈ 8.5-10.5) may provide habitable environments similar to the terrestrial Lost City hydrothermal vent system.
Here we present an analysis of Cassini Cosmic Dust Analyzer (CDA) spectra of plume ice grains detected in the E ring. By comparison with laboratory mass spectra, the CDA spectra showing low mass (<100 u) features have been categorized into: N- and O-bearing volatile organic compounds (VOCs), single-ring aromatics, or mixtures of several these compounds, all found at mmol concentrations in the ice grains [4]. Maintaining consistency between the CDA ice grain spectra, the gas plume composition and adsorption energetics [5], we identify low mass carbonyls (with acetic acid and/or acetaldehyde most suitable) and amines (particularly (di)methylamine and/or ethylamine) within E ring grains [4], and by extension, in the Enceladean ocean. These low mass amines, carbonyls and aromatic compounds are ideal precursors for e.g. mineral-catalyzed [6,7] Friedel-Crafts hydrothermal reactions, potentially generating biogenically-relevant organic compounds, such as amino acids, in the warm depths of Enceladus' ocean. Transported from hydrothermal vents at depth to the oceanic surface, the dissolved volatile compounds evaporate, then adsorb onto ice grains as they develop and rise through fractures in Enceladus' icy crust. In contrast the detected aromatics are likely to be low vapor pressure, poorly-soluble compounds, aerosolized by bubble bursting (e.g. [8]). References: [1] Choblet et al., Nat. Astr., 2017 [2] Hsu et al., Nature, 2015 [3] Waite et al., Science, 2017 [4] Khawaja et al., MNRAS, 2019 [5] Bouquet et al., ApJ, 2019 [6] Barge et al., PNAS, 2019 [7] Menez et al., Nature, 2018 [8] Postberg et al., Nature, 2018- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P24A..06K
- Keywords:
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- 4850 Marine organic chemistry;
- OCEANOGRAPHY: BIOLOGICAL AND CHEMICAL;
- 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6282 Enceladus;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 8450 Planetary volcanism;
- VOLCANOLOGY