Analog Sites for Mars Missions II (2013)
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PARALLELS BETWEEN STRATOSPHERIC MICROBIOLOGY AND MARS ASTROBIOLOGY MISSIONS. D. J. Smith1 and A. C. Schuerger2, 1NASA Kennedy Space Center, Surface Systems Office, Mail Code: NE-S, KSC, FL, 32899,
[email protected], 2University of Florida, 505 Odyssey Way, Exploration Park, N. Merritt Island, FL, 32953,
[email protected].
Introduction: Microbes can reach the stratosphere (about 17 to 50 km above sea level (ASL)) by strong upward winds, violent storms, volcanic eruptions, and aircraft [1]. Aerosol exchange in the tropopause is increasing due to climate change [2], suggesting a greater numbers of microbes will cross between the troposphere and stratosphere in the coming years. The exploration of Earth’s upper atmosphere can help constrain the search for potentially habitable environments on other worlds. Like Mars, the stratosphere is extremely dry, frozen, irradiated, and hypobaric [1]. Mission Description: Detecting microbial signatures without false positives is a critical feature shared by stratospheric and solar system exploration. In either context, an unacceptable outcome is the inability to discriminate between in situ microorganisms and terrestrial contaminants hitchhiking on flight hardware. Sterility and contamination controls developed by future missions to the stratosphere will likely employ multiple layers of containment, along with unique positive and negative controls or in-flight sterilization measures, which will contribute to development of technologies and procedures for preventing the forward contamination of other worlds by spacecraft. Lessons learned in the stratosphere might also advance methods for life detection experiments on Mars. Not only are scientific requirements comparable (i.e., detecting very low microbial biomass), but the rarified near-space environment of the stratosphere imposes similar operational parameters on flight hardware. Other Mars analogs (e.g., Antarctica) lack key features of the martian environment, including hypobaria and extreme UV irradiation levels. Access Using Balloons: Large scientific balloons are a reliable and efficient way of reaching the upper atmosphere and can be used up to about 50 km ASL [3]. Balloons are made of a thin polyethylene film, inflated with helium, and expand up to 140 m in diameter during ascent through the increasingly rarefied atmosphere. Two to three hours after launch, balloons reach the target float altitude and travel in the prevailing wind direction, carrying atmospheric sampling instruments on a gondola suspended underneath the balloon. Payloads eventually return to the surface on a parachute. Sampling time aloft depends on payload weight (typically < 3600 kg), target altitude, launch site, and weather conditions. Recent advances in ultra-
long duration ballooning allowed a payload to remain aloft for 55 days at 39 km ASL [4]. Scientific Merit: Both Mars exploration and balloon-based stratospheric microbiology experiments must detect microbial signatures without false positives (i.e., contamination) on flight hardware that operates autonomously in harsh conditions. Balloon-based stratospheric microbiology research can also improve our understanding of UV-resistant microbial species. Taxa capable of surviving the rigors of transport (e.g., desiccation and UV irradiation) have been documented at extreme altitudes [1]. Cell pigmentation, UV repair pathways, and the ability to form spores are a few examples of what might be considered atmospheric specialization. Understanding what microbes survive in the stratosphere might inform the search for life on Mars and also contribute to planetary protection policies for missions, since post-landing UV may not kill all terrestrial microbes on the exterior of spacecraft [5]. Logistic and Environmental Constraints: Before molecular methods in microbiology emerged, stratospheric microbiology studies had to rely upon culturing, which can miss most microbes present from environmental samples [6]. Acquiring molecular-based microbiology data with stratospheric samples has not yet been achieved because bioaerosols are diluted in the voluminous atmosphere and density decreases with altitude [3]. New air sampling technologies must be developed in order to collect sufficient biomass for employing molecular assays. Furthermore, if Mars missions with life detection instrument payloads are first required to demonstrate technology readiness in the upper atmosphere (e.g., instrument sensitivity, in-flight sterilization or contamination containment), access to the stratosphere must become easier. Perhaps a cooperative agreement between NASA Balloon Program Office and Mars Exploration Program would encourage and enable the use of this underexplored, compelling terrestrial analog site. References: [1] Smith D. J. et al. (2011) Aerobiologia, 27, 319-332. [2] Randel W. J. and Jensen E. J. (2013) Nat. Geosci., 6, 169-176. [3] Yang Y. et al. (2009) Biol. Sci. in Space, 23, 151-163. [4] Ward J. E. et al. (2013) Bull. Amer. Phys. Soc., Abstract #BAPS.2013.APR.L14.8. [5] Schuerger et al., 2013, Astrobiology, 13, 115-131. [6] Gandolfi I. et al. (2013) Appl. Microbiol. and Biotech., 97, 4727-4736.
