Inadvertently Finding Earth Contamination on Mars Should Not Be a Priority for Anyone
Total Page：16
File Type：pdf, Size：1020Kb
ASTROBIOLOGY Volume 18, Number 2, 2018 ª Mary Ann Liebert, Inc. DOI: 10.1089/ast.2017.1785 Inadvertently Finding Earth Contamination on Mars Should Not Be a Priority for Anyone John D. Rummel1 and Catharine A. Conley2 aire´n et al. (2018, in this issue) identify ‘‘the most out in An Exobiological Strategy for Mars Exploration from Fimportant scientific question driving Mars exploration; 1995 (Exobiology Program Office, 1995). One of the points that is, has life occurred on Mars, in the past or at present, and emphasized in this strategy is that it doesn’t make sense to how can we best answer this question with future Mars go to Mars trying to search for extant life without having missions?’’ It should be stated up front that both of us also a specific, qualified target for such a search. Further, upon believe that a search for martian life, extinct and/or extant, is finding such a target, it’s necessary to control against false- among the highest priorities for Mars science. Accepting that positive indications of life caused by Earth-sourced con- this objective is not up for debate, we further contend that tamination (Space Studies Board, Task Group on Planetary such a high-priority search should be protected at a level Protection, 1992; Exobiology Program Office, 1995). consistent with its importance—that is, not be conducted in a Specifically the Strategy states, way that could obscure evidence of martian life while care- . It is evident that several hypothetical alternative niches lessly introducing our own to the most hospitable places for for life on Mars have been suggested in the exobiological Earth life on Mars—Special Regions. literature. As of this writing, however, these remain to be This is in contrast to the specifics proposed by Faire´n located and characterized. Thus, the initial thrust of the et al. (2017), which involve searching for martian life using strategy for extant life on Mars must be to determine whether spacecraft that carry Earth contamination at levels likely to or not these environments actually exist. Only with the ac- confound the desired result—and potentially other future quisition of this fundamental information will it be reason- human objectives at Mars. Despite what Faire´n et al. (2018) able, from the point of view of extant biology, to probe such seem to believe, current planetary protection policies are not putative environments with landed instrumentation (Exo- to blame for the priorities of the NASA Mars Exploration biology Program Office, 1995). Program—or other space agencies’ exploration programs— Until a likely place on Mars that may currently support nor do arguments in favor of continued adherence to plan- life has been identified, searching for extant martian life is etary protection policies, as they have been developed over premature. If life was once widespread on Mars, and is not decades by the international scientific community, ‘‘illus- now, there should be much evidence for ancient martian life trate why we are not searching for life on Mars today and spread around the planet, and in less contaminable places why we haven’t done so during the last decades.’’ than those that qualify as modern Special Regions. Hence, Rather than revisiting the contentions of previous articles ‘‘searching for life on Mars’’ currently prioritizes looking point-by-point, we here consider three decisions that need to for conditions that would preserve biomarkers expected to be made when addressing the question, posed by Faire´n et al., reflect ancient Mars, rather than present-day Mars, because of how to detect martian life with future missions. These are we think we know where to look for them. In fact, one of the authors of the Faire´n et al. papers is a (1) Where should we look for martian life? Downloaded by Guangxi University for Nationalities from online.liebertpub.com at 02/18/18. For personal use only. coauthor of a recent paper entitled ‘‘Critical Assessment (2) What are the concerns associated with Earth of Analytical Techniques in the Search for Biomarkers on contamination? Mars: A Mummified Microbial Mat from Antarctica as a (3) Which missions should be sent, and when? Best-Case Scenario’’ (Blanco et al., 2017). We agree with In reviewing how the Mars exploration community has this approach. Detecting biomarkers of ancient (and possibly evaluated these options over time, we illustrate the thought extinct, microbial-mat) life may, indeed, be the best way to processes that have contributed to their development—which find martian life. follow a train of logic that applies equally well to future missions. Despite this, Faire´n et al. (2018) seem to feel that the Space Studies Board advice to target locations with high preservation potential runs counter to ‘‘the actual priorities, 1. Where Should We Look for Martian Life? goals, and desires of the Mars community’’—but they do not The NASA Mars Exploration Program, post-Viking, has cite references that identify even one specific location on not been actively searching for extant life on Mars because Mars where a search for extant life is advocated as the the program has effectively been following the roadmap laid primary mission goal. To justify this ‘‘community’’ 1SETI Institute, Mountain View, California. 2NASA Headquarters, Washington, DC. 108 FINDING MARTIAN LIFE ON MARS 109 statement, Faire´n et al. (2018) listed the following refer- missions has run into several billions of dollars, so the ences: McKay et al. (2013), Grossman (2013), Heldmann fractional cost of planetary protection measures could be et al. (2014), Vago et al. (2015), King (2015), Levin and under 10%. Again, it becomes a question of priorities—if Straat (2016), Gordon and Sephton (2016), Smith et al. one really wanted to study a Mars Special Region, this (2017), Xie et al. (2017), Niles et al. (2017), Ehlmann et al. would be an acceptable cost. However, because access to (2017). These references generally relate to the concept of Special Regions was not identified as a high priority in life detection on Mars, but the advocacy of these references Planetary Science Decadal Surveys, the investments neces- for the assertion that a search for extant life is the highest sary to reestablish those capabilities (linking back to the priority for Mars exploration is decidedly weak. In contrast, Viking experience) have not been made. one of the strongest reasons given for doing that search is This does not mean that it is suddenly sensible to allow related to ensuring the safety of future human explorers access to Special Regions by spacecraft that carry viable against a possible biological threat—exactly what planetary Earth organisms, as Faire´n et al. propose, at least not without protection is intended to accomplish and what COSPAR evaluating the potential consequences, and as a global policy specifies. community—not just the Mars community—deciding that For a summary of how each of these references maps to a we’re willing to accept them. search for extant life on Mars, see Table 1. In the context of introducing Earth contamination to Our previous statement that ‘‘the Mars community is not Mars, Faire´n et al. make the following three-point claim: convinced that a mission to attempt detection of extant . the current robotic exploration of Mars will have little (if martian life is a high priority’’ is well-supported by the any) impact on potential martian biospheres or on our efforts recommendations of the most recent Planetary Science for searching for active life on Mars, because (i) the micro- Decadal Survey (Space Studies Board, Committee on the bial burden carried by unmanned robots is minimal and not Planetary Science Decadal Survey, 2012) on Planetary renewable and, most importantly, known and identifiable; (ii) Science priorities through 2022. A mission to go to a Special the martian surface is bactericidal in nature; and (iii) we Region and search for extant martian life, although espoused know how to distinguish an Earth microorganism from po- by Faire´n et al. (2017, 2018), was not among the missions tential martians. prioritized by the Space Studies Board in 2012. Note that, in As it turns out, the first two of these claims are already the eyes of NASA and the US Congress, the Planetary incorporated into the COSPAR Planetary Protection Science Decadal Survey documents ‘‘the actual priorities, Policy—and the third is not supported by any available data. goals, and desires of the Mars community.’’ It may be true, as Faire´n et al. stated, that ‘‘the Mars community, including NASA, always points to life detection 2.1. Microbial burden on robotic spacecraft as a number-one priority in Mars exploration,’’ but it is It is thanks to planetary protection cleanliness require- important to note that ‘‘life detection’’ does not necessarily ments that the microbial burden on Mars robotic spacecraft is mean going to Special Regions to try to culture or sequence ‘‘minimal’’—andalso‘‘notrenewable’’solongasthemicrobial microbes. In fact, although we consider this evident lack of passengers are not introduced into places where they can grow interest unfortunate, it would be even more unfortunate to (the definition of Special Regions). However, current technolo- permit access to Special Regions in the absence of appro- gies to identify microbial populations carried on spacecraft are priate planetary protection precautions. inadequate and would be even less well-developed if not re- quired for planetary protection. A reasonable genetic inventory 2. What Are the Concerns Associated of microbial contaminants in the extremely oligotrophic envi- with Earth Contamination? ronments of spacecraft assembly clean rooms may be achievable by using technologies developed for other fields but will re- The current definition of Special Regions is based on the quire further advances in sample collection and analysis— characteristics of possible contaminating Earth organisms, only developments that are currently being pursued by planetary (Rummel et al., 2014).