Abstract
With the discovery of the persistent jets of water being ejected to space from Enceladus, an understanding of the effect of the space environment on potential organisms and biosignatures in them is necessary for planning life detection missions. We experimentally determine the survivability of microbial cells in liquid medium when ejected into vacuum. Epifluorescence microscopy, using a lipid stain, and SEM imaging were used to interrogate the cellular integrity of E. coli after ejected through a pressurized nozzle into a vacuum chamber. The experimental samples showed a 94% decrease in visible intact E. coli cells but showed a fluorescence residue in the shape of the sublimated droplets that indicated the presence of lipids. The differences in the experimental conditions versus those expected on Enceladus should not change the analog value because the process a sample would undergo when ejected into space was representative. E. coli was selected for testing although other cell types could vary physiologically which would affect their response to a vacuum environment. More testing is needed to determine the dynamic range in concentration of cells expected to survive the plume environment. However, these results suggest that lipids may be directly detectable evidence of life in icy world plumes.
Highlights
In the search for life outside of Earth it is necessary to quantify the potential abundances of biosignatures, including whole single-celled organisms, in target environments
Any putative life possible in the interior ocean of an icy moon is adapted to a liquid water environment
This work has started to fill in the uncertainties about the survivability of biosignatures in icy world plumes
Summary
In the search for life outside of Earth it is necessary to quantify the potential abundances of biosignatures, including whole single-celled organisms, in target environments. Sample collection techniques aside, which can affect the integrity of the biosignatures being collected, the physical processes of the target environment can have an effect on the retention of biosignatures. Knowledge of the types and expected quantities of these biosignatures will enable detection strategies and sensitivity limits to be set for proposed life detection instrumentation. To this end, an understanding of the effect of the physical environment on organisms and biosignatures is essential. Enceladus has a sub-ice-shell global ocean [1] of salty water [2]
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