Detecting cellular biosignatures from single salt-rich ice grains emitted from Enceladus or Europa
Authors: Ackley Mirandah , Dannenmann Marie , Napoleoni Maryse , Klenner Fabian , Bönigk Janine , Olsson-Francis Karen , Postberg Frank 
Published: July 2024

Icy moons with a liquid subsurface ocean, such as Europa7 and Enceladus16, are prime candidates in the search for extraterrestrial life. For future spaceflight missions, the identification of biosignatures with onboard mass spectrometers (MS) will be essential. NASA and ESA&#8217;s Cassini-Huygens spacecraft, which passed nearby to Enceladus and sampled ice grains from the icy moon&#8217;s cryovolcanic plume using low resolution impact ionization mass spectrometry, has already identified a variety of organic material originating from the moon&#8217;s subsurface ocean6,11. In upcoming missions, such as NASA&#8217;s Europa Clipper, the use of higher resolution mass spectrometers will be crucial for clearer identification of organic compounds5,13.The Planetary Sciences group at Freie Universit&#228;t Berlin is specialized in simulating mass spectra obtained from ice grains in space by a Laser Induced Liquid Beam Ion Desorption Mass Spectrometer (LILBID-MS)17. Such experiments have proven capable of accurately identifying and quantifying biomolecules in a water-ice matrix, such as amino acids, peptides, sugars, and fatty acids from within cells4, while distinguishing between molecular patterns with biotic or abiotic origins8. They have also demonstrated how to identify cell material from within a single pure-water ice grain emitted from Enceladus or Europa9. However, there are still gaps in our knowledge of to what extent salts affect the spectrometric fingerprints of biosignatures.Such salt concentrations are highly relevant for the ocean and surface of icy moons, where potential biosignatures might be found in water or ice with salinity levels similar to or greater than that of Earth&#8217;s oceans. On Enceladus, the ocean contains salt concentrations ranging from 0.07 - 0.3 M NaCl, dependent on depth and ocean layer2,12. On Europa, the abundance and composition of salts in the ocean is not well defined, but existing estimates suggest that the ocean is dominated by NaCl and MgSO4 3. Previous research indicates that the total hydrosphere of Europa contains &#8764;0.6 M of total dissolved salts14, ranging from 0.01 M MgSO4 and NaCl in less salty ocean waters10 to 2.4 M in mantle pore fluids or localized hyper-saline regions15. Biosignatures entrained in ice grains originating from these regions of Europa or Enceladus would contain far higher salinity levels than have previously been studied, and these levels of salinity are known to interfere with the visibility of organics in mass spectral data1,8, 18, 19.&#160;This research project studies how salinity levels and various types of salts comparable to those found on the icy moons may affect mass spectral biosignature readings. To achieve this, the psychrophilic extremophile Sphingopyxis alaskensis is submerged in water-based solutions with salt concentrations similar to that of Enceladus and Europa. The mass spectra of the cells are then measured using MS laboratory instruments to determine what biosignatures might be detectable in single salt-rich ice grains that contain cell material.&#160;&#160;Understanding how salts affect the way cell material is presented in mass spectral data is conducive to&#160; the identification of organic biosignatures in future spaceflight missions, such as Europa Clipper. This research project will help to strengthen our understanding of biosignature detection, enhancing the capability of spaceborne instruments to detect the presence or absence of biosignatures with high confidence.&#160;(1) Annesley, T. M., 2003, Clinical Chemistry, vol. 49, pp. 1041&#8211;1044, https://doi.org/10.1373/49.7.1041.&#160;
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