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Identifying Cell Material in a Single Ice Grain Emitted from Enceladus or Europa

Presentation #108.05 in the session Astrobiology and Origins of Life (Oral Presentation)

Published onOct 23, 2023
Identifying Cell Material in a Single Ice Grain Emitted from Enceladus or Europa

Ice grains emitted from Enceladus or Europa can be individually sampled by impact ionization mass spectrometers, such as the Cosmic Dust Analyzer (CDA)1 on board Cassini or the SUrface Dust Analyzer (SUDA)2 on board Europa Clipper. CDA data of ice grains collected in the Saturnian System revealed that Enceladus’s ocean is salty3, contains phosphates4 and a variety of organic compounds5. Both phosphates and complex organics occur in only a few % of plume ice grains, highlighting the importance of analysis of single grains compared to a diluted and mixed bulk sample. The complex organics are thought to be entrained in ice grains from an organic film at the oceanic surface5. Cell material, if present, would likely reside in a fraction of such grains and with that could be found in less than 1% of ice grains.

To simulate such a scenario, we here report laboratory experiments with Sphingopyxis alaskensis, potentially capable of fitting into µm-sized ice grains. We used Laser Induced Liquid Beam Ion Desorption (LILBID) – a technique proven to simulate impact ionization mass spectra of ice grains recorded in space6. This includes the detection of potential biosignatures in the grains7,8.

In both polarity mass spectra, we clearly identify signatures of S. alaskensis. Our experiments show that even if only 0.01% of the cell’s constituents were contained in an ice grain (2 μm in diameter) emitted by an Enceladus-like plume, the bacterial signatures would be apparent in data recorded by SUDA-type instruments. Such an instrument is capable of analyzing 10.000-100.000 single ice grains during a plume passage, allowing to assess biosignatures that are present in only 1 out of 100,000’s of grains sampled during a multiple flyby mission.

A scenario in which 0.01 % of a cell is present in 1% or 0.001% of plume grains resembles a cell density of 2 x 105 or 2 x 102 cells/mL, respectively, if integrated over the entire icy material in the plume. The detection of such low cell densities will be hard to achieve by any other analytical method without a lander. The capability to analyze the composition of individual ice grains allows to assess the apparent compositional heterogeneity of the plume with salts and organics that have already been separated during formation.

1Srama et al. (2004) Space Sci Rev 114, 465–518.

2Kempf et al. (2014) EPSC 9, EPSC2014–229.

3Postberg et al. (2009) Nature 459, 1098–1101.

4Postberg et al. (2023) Nature 618, 489-493.

5Postberg et al. (2018) Nature 558, 564–568.

6Klenner et al. (2019) Rapid Commun Mass Spectrom 33, 1751–1760.

7Klenner et al. (2020) Astrobiology 20, 1168–1184.

8Dannenmann et al. (2023) Astrobiology 23, 60–75.

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