A Method for Choosing the Best Samples for Mars Sample Return

Abstract

Success of a future Mars Sample Return mission will depend on the correct choice of samples. Pyrolysis-FTIR can be employed as a triage instrument for Mars Sample Return. The technique can thermally dissociate minerals and organic matter for detection. Identification of certain mineral types can determine the habitability of the depositional environment, past or present, while detection of organic matter may suggest past or present habitation. In Mars' history, the Theiikian era represents an attractive target for life search missions and the acquisition of samples. The acidic and increasingly dry Theiikian may have been habitable and followed a lengthy neutral and wet period in Mars' history during which life could have originated and proliferated to achieve relatively abundant levels of biomass with a wide distribution. Moreover, the sulfate minerals produced in the Theiikian are also known to be good preservers of organic matter. We have used pyrolysis-FTIR and samples from a Mars analog ferrous acid stream with a thriving ecosystem to test the triage concept. Pyrolysis-FTIR identified those samples with the greatest probability of habitability and habitation. A three-tier scoring system was developed based on the detection of (i) organic signals, (ii) carbon dioxide and water, and (iii) sulfur dioxide. The presence of each component was given a score of A, B, or C depending on whether the substance had been detected, tentatively detected, or not detected, respectively. Single-step (for greatest possible sensitivity) or multistep (for more diagnostic data) pyrolysis-FTIR methods informed the assignments. The system allowed the highest-priority samples to be categorized as AAA (or A*AA if the organic signal was complex), while the lowest-priority samples could be categorized as CCC. Our methods provide a mechanism with which to rank samples and identify those that should take the highest priority for return to Earth during a Mars Sample Return mission. Key Words: Mars—Astrobiology—Search for Mars' organics—Infrared spectroscopy—Planetary habitability and biosignatures. Astrobiology 18, 556–570.

A Spectral Comparison of Jarosites Using Techniques Relevant to the Robotic Exploration of Biosignatures on Mars

“…Our ability to successfully search for evidence of Earth-like life in extraterrestrial planetary environments is inherently dependent on our ability to recognize evidence of past or present life in analogous terrestrial samples. Additionally, there are time and resource constraints when conducting in situ experiments during the robotic exploration of planetary bodies and advances in our search for biosignatures on Mars can be made by conducting systematic investigations of martian analogue materials here on Earth (e.g., [25,26,29,30]); and the data obtained from such studies can be used to inform future missions and guide the search for biosignatures in martian sediments (e.g., [26,31]).…”

Evolutionary History of Bioessential Elements Can Guide the Search for Life in the Universe

“…[14,[23][24][25][26][27][28] Within the next decade, the search for life on other worlds will require difficult decisions about Mars sample selection, Solar System mission destinations, and exoplanet observational priorities. [26,27,[29][30][31] Even in the most fortunate circumstance, we will still face the challenge of interpreting potential signs of life and filtering false positives. [25,32,33] These decisions and interpretations will be guided by knowledge of how the physicochemical characteristics of various planetary environments determine their habitability, how they shape the emergence and evolution of life, and how they affect our ability to detect of life.…”

“…Understanding why life selects for certain elements is needed to guide the search for life because our ability to gauge the potential of life's existence elsewhere in the universe is inevitably rooted in predictions regarding the chemical demands of possible alien biochemistries [14,23–28] . Within the next decade, the search for life on other worlds will require difficult decisions about Mars sample selection, Solar System mission destinations, and exoplanet observational priorities [26,27,29–31] . Even in the most fortunate circumstance, we will still face the challenge of interpreting potential signs of life and filtering false positives [25,32,33] .…”