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Understanding Hypervelocity Sampling of Biosignatures in Space Missions

Authors
  • Jaramillo-Botero, Andres
  • Cable, Morgan L.
  • Hofmann, Amy E.
  • Malaska, Michael
  • Hodyss, Robert
  • Lunine, Jonathan
Type
Published Article
Journal
Astrobiology
Publisher
Mary Ann Liebert
Publication Date
Mar 25, 2021
Volume
21
Issue
4
Pages
421–442
Identifiers
DOI: 10.1089/ast.2020.2301
PMID: 33749334
PMCID: PMC7994429
Source
PubMed Central
Keywords
Disciplines
  • Research Articles
License
Green

Abstract

The atomic-scale fragmentation processes involved in molecules undergoing hypervelocity impacts (HVIs; defined as > 3 km/s) are challenging to investigate via experiments and still not well understood. This is particularly relevant for the consistency of biosignals from small-molecular-weight neutral organic molecules obtained during solar system robotic missions sampling atmospheres and plumes at hypervelocities. Experimental measurements to replicate HVI effects on neutral molecules are challenging, both in terms of accelerating uncharged species and isolating the multiple transition states over very rapid timescales ( < 1 ps). Nonequilibrium first-principles-based simulations extend the range of what is possible with experiments. We report on high-fidelity simulations of the fragmentation of small organic biosignature molecules over the range v = 1 − 12 km/s, and demonstrate that the fragmentation fraction is a sensitive function of velocity, impact angle, molecular structure, impact surface material, and the presence of surrounding ice shells. Furthermore, we generate interpretable fragmentation pathways and spectra for velocity values above the fragmentation thresholds and reveal how organic molecules encased in ice grains, as would likely be the case for those in “ocean worlds,” are preserved at even higher velocities than bare molecules. Our results place ideal spacecraft encounter velocities between 3 and 5 km/s for bare amino and fatty acids and within 4–6 km/s for the same species encased in ice grains and predict the onset of organic fragmentation in ice grains at > 5 km/s, both consistent with recent experiments exploring HVI effects using impact-induced ionization and analysis via mass spectrometry and from the analysis of Enceladus organics in Cassini Data. From nanometer-sized ice Ih clusters, we establish that HVI energy is dissipated by ice casings through thermal resistance to the impact shock wave and that an upper fragmentation velocity limit exists at which ultimately any organic contents will be cleaved by the surrounding ice—this provides a fundamental path to characterize micrometer-sized ice grains. Altogether, these results provide quantifiable insights to bracket future instrument design and mission parameters.

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