CURRENT UNDERSTANDING OF THE PHYSICAL AND CHEMICAL LIMITS OF LIFE
Ion Tolerance and Preferential Selectivity of a Lipid in Mixed Lipid Systems: An Evolutionary Approach to Modern Membranes
Punam Dala, Putu Ustriyana, and Nita Sahai, University of Akron
Protocell membranes may have been composed of single chain amphiphiles (SCAs) due to their prebiotic availability, but SCA membranes are disrupted by divalent cations in aqueous solutions. Mixed SCA vesicles are known to be more resistant to the fatal effects of dissolved Mg2+ and Ca2+. Here we examined the potential role of Mg2+ as an environmental selection pressure in the transition of fatty acid membranes to mixed SCA-phospholipid membranes and, finally, to phospholipid membranes. The Mg-tolerance of binary mixtures of oleic acid (OA) with palmitoyl-2-oleoylphosphatidylcholine (POPC) was determined. The fatal magnesium concentration, [Mg2+]fatal, was defined as the concentration of Mg2+ required to disrupt ~100% of vesicles (200 nm extruded). Membrane disruption was determined by measuring the decrease in fluorescence intensity of a membrane-soluble dye, naphthopyrene, that had been previously entrapped in the vesicle membranes. The relative distribution of lipid into vesicles and amorphous aggregates was also estimated by dynamic light scattering and optical microscopy. The [Mg2+]fatal increased drastically with increasing relative POPC content from 5 mM for pure OA, to 40 mM for [OA]/[POPC] = 1:1, and >80 mM for pure POPC (total lipid concentration = 2 mM, pH 8.5). We propose two distinct mechanisms by which magnesium-tolerance of the mixed lipid systems increases. First, as confirmed by zeta potential measurements, POPC (zwitterionic head group) stabilizes the mixed-lipid vesicles by decreasing the relative negative charge density of the vesicles, so more Mg2+ is needed to disrupt the vesicles. Second, Mg2+ was found to preferentially bind to and abstract OA from OA-POPC mixed lipid membranes, resulting in lower [OA]/[POPC] ratio in the vesicles as compared to the initial ratio. Quantitation of OA and POPC concentration in the vesicles was achieved by filtration (220 nm pore) to remove Mg2+-lipid aggregates and high-performance liquid chromatography (HPLC) analysis of the filtrate. This is the first time that a cation has been shown to directly change the composition of a lipid membrane. The significantly greater Mg-tolerance of SCA-phospholipid vesicles may hold implications for the evolutionary selection of phospholipid membranes and for accommodating Mg2+promoted processes such as RNA polymerization.
Non-Enzymatic RNA Polymerization at the Mineral-Water Interface: A Search for a Potential Adsorption-Polymerization Relationship
Hussein Kaddour, Selim Gerislioglu, Toshi Miyoshi, Chrys Wedemiotis, and Nita Sahai, University of Akron
The extent of adsorption of nucleotide or amino acid monomers at mineral surfaces and subsequent surface-catalyzed polymerization to RNA or peptides is a widely assumed potential role of minerals in the origins of life. Few studies, however, have critically examined this assumption. Here, we investigated the relationship, if any, between the adsorption of adenosine monophosphate (AMP) nucleotide on a wide range of minerals (oxides, oxyhydroxide, carbonate, sulfide, aluminosilicate) and the potential catalytic activity of these minerals in the nonenzymatic polymerization of AMP, by using ultraviolet-visible (UV/Vis) spectroscopy, HPLC, mass spectrometry (MALDI) and solid-state 31P NMR spectroscopy. Adsorption on AMP, which is negatively charged at pH 8, increased with isoelectric point (positive surface charge) of the mineral reaching a maximum with zincite (ZnO, IEP ~ 8). However, polymerization on montmorillonite, a negatively charged clay mineral, was better than on ZnO, consistent with the work of Jim Ferris, Prakash Joshi, and co-workers. The nuclear magnetic resonance spectroscopy results showed that the AMP monomer was bonded via the phosphate moiety to the ZnO surface, thereby preventing condensation between adjacent AMP monomers. In contrast, the phosphate moiety was relatively unconstrained at the montmorillonite surface, which is interpreted to indicate that the adsorbed conformation allowed interaction between phosphate moieties of adjacent AMP monomers. Thus, the configuration of the adsorbed AMP monomer with respect to the mineral surface and to the neighboring AMP molecule is more important than the total mass of adsorbed monomer for surface-catalyzed polymerization.
HABITABLE ENVIRONMENTS IN THE SOLAR SYSTEM AND EXTRASOLAR PLANETARY SYSTEMS
The Icebreaker Life Mission: Why Search for Modern Life on Mars and How to Do It
Carol Stoker and C.P. McKay, NASA
Ground ice in the northern plains of Mars hosts habitable conditions for life periodically, most recently during high obliquity, 0.5 to 10 Myr ago. Habitable conditions include (1) pressure above the triple point of liquid water; (2) ice near the surface as a source of liquid water; and (3) high summer insolation at orbital tilts >35° (present 25°), equivalent to levels of summer sunlight in Earth’s polar regions at the present time. Terrestrial permafrost communities are examples of possible life in the ground ice. Studies in permafrost have shown that microorganisms can function in ice-soil mixtures at temperatures as low as −20°C, living in thin films of interfacial water. In addition, it is well established that ground ice preserves living cells, biological material, and organic compounds for long periods of time, and living microorganisms have been preserved under frozen conditions for thousands and sometimes millions of years. Similar biomolecular evidence of life could have accumulated in the ice-rich regolith on Mars. The Mars Icebreaker Life mission has been proposed to search for life there. Science goals are: (1) search for biomolecular evidence of life; (2) search for organic matter from either exogeneous or endogeneous sources using methods that are not affected by the presence of perchlorate; (3) characterize oxidative species that produced reactivity of soils seen by Viking; and (4) assess the habitability of the ice-bearing soils. The payload includes a 1-m drill that brings cuttings samples to the surface where they are delivered to three instruments: the Signs of Life Detector (SOLID) for biomolecular analysis, Laser Desorption Mass Spectrometer (LDMS) for broad spectrum organic analysis, and Wet Chemistry Laboratory (WCL) for detecting soluble species of nutrients and reactive oxidants. The poster will describe the mission and instruments.
How Can We Know that We Are Not Sampling Bacteria in the Clouds of Venus If Their Physical Properties Are Similar?
Sanjay Limaye, University of Wisconsin
There is a great similarity in the physical properties of Th. ferrooxidans and similar species and those of the cloud particles on Venus. Further, these types of bacteria also absorb ultraviolet below 400 nm and have variable transmittance at 2 to 3 microns, key characteristics of Venus clouds. Recent research suggests that Venus could have harbored liquid water on its surface for about 2 billion years, so it is conceivable that life migrated to the clouds when surface became warmer. How can we look for the distinctive properties of the clouds to know if the UV absorber is organic or inorganic?
The Habitable Zone: A Planetary Scientist’s Perspective
David Paige, UCLA
The habitable zone is generally defined as the region around a star that can support liquid water given sufficient pressure. In our own solar system, this region is not limited to a small range of distances from the Sun, but includes a diverse-range of surface, subsurface, and atmospheric environments that extend from Mercury to the outer solar system. Conversely, not all planetary bodies within the Sun’s “Goldilocks Zone” are actually habitable, as evidenced by the Earth’s Moon. What we know about the habitability of our own solar system through time can help guide our search for habitable environments around other stars.
Plausible Organic Chemistry Might Precede the Early Development of Life?
Sayali Mulay, TYBSc. Biotechnology, Fergusson College, Pune, India
Objective: The Urey-Miller-Miller experiment gave a content explanation of the possibility of formation of organic molecules from the inorganic molecules by depicting the early Earth conditions. By simulating the same experiment with Venusian gases and conditions, potential molecules regarded as the early building blocks of life that might precede the development of life in the Venusian clouds can be stated.
Introduction: The Venusian clouds present at 50 to 60 km from the ground have favourable environment for life to originate and sustain. These clouds are rich in carbon dioxide and nitrogen. Traces of other gases such as water vapour, carbon monoxide, and sulphur dioxide are present. Acidic environment due to presence of hydrochloric acid and sulphuric acid is seen. Atmospheric pressure is 1 atm, and temperature ranges from 76°C to 10°C with the altitude. With these conditions, experiments can be carried out, and the formation of organic compounds can be observed, if any.
Methods: sterile glassware must be used to carry out this experiment. The gases used will be carbon dioxide, nitrogen, water vapour, carbon monoxide, and sulphur dioxide in ratio as per the presence of the same in the Venusian clouds. Fluctuating low electric current can be used as there are few evidences of lightning strikes on Venus and Whistler waves. Otherwise, UV radiation can also be used, although the UV flux penetrating into the clouds at 50 to 60 km from the ground is much less. Water vapour at about 76°C can be used.
Results: Hypothesis is such that, due to presence of carbon and nitrogen with a source of electricity, organic compounds should be obtained. These organic compounds studied show that possible microbial world that can exist in the clouds can be found out using characters of different extremophilic microbes on Earth. This resulting “organic tar” (hypothesised) can also be used as a medium to isolate Venusian microbes in the clouds (hypothesised) as a sample return mission.
Conclusion: Simulation of Urey-Miller experiment in the laboratory with Venusian environmental factors can result into following hypothesis: (1) organic chemistry is flourishing in the Venusian clouds, (2) obtained organic compounds can be responsible factors for the plausible preceding life on Venus, and (3) Venus sample return mis-
sions can be planned with the obtained “organic tar” as the source in the media to isolate already hypothesised microbial life on Venus.
Identification of Clays on Mars and Why They Are Important for Astrobiology
Janice Bishop, SETI Institute
Phyllosilicate deposits on Mars provide an opportunity to evaluate aqueous activity and the possibility that habitable environments may have existed during Mars’ early history. Analysis of visible/near-infrared (VNIR) reflectance spectra acquired by the Mars Reconnaissance Orbiter (MRO) Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument has revealed thick, complex profiles of phyllosilicates on the surface of Mars that are consistent with long-term aqueous activity and active chemistry. The ancient phyllosilicates in places such as Mawrth Vallis could have served as reaction centers for organic molecules. Previous experiments even suggest that phyllosilicates could have played a role in the origin of life. Regardless of whether life formed on early Mars or not, evaluating the type and thickness of clay-bearing units on Mars provides insights into plausible aqueous processes and chemical conditions both during the time of formation of the phyllosilicates, but also the subsequent period following their formation. Changes in iron redox state and in phyllosilicate chemistry indicate an active geochemical environment during the time of clay formation. In some environments, clays are associated with carbonates and neutral environments, while in others they are associated with sulfates and acid alteration. Also, recent identification of poorly crystalline aluminosilicates at the top of the clay profile indicates a change in climate from the environment supporting liquid water and formation of clay minerals to an environment where liquid water was no longer abundant on the surface. Thus, characterizing the type of clays and associated minerals on Mars from orbit provides clues to when and where Mars may have been habitable in the past.
Finding a Planet’s Heartbeat: Unexpected Results from Patient Mars
Vlada Stamenkovic, Lewis Ward, and Woody Fischer, Caltech, and Michael Mischna and Michael Russell, JPL
A planet, from deep interior to atmosphere, has the potential to generate essential nutrients and redox gradients critical for the emergence and the evolution of life. Here, I will present preliminary results on two very different large-scale planetary processes that generate nutrients and redox gradients and discuss the implications for Earth and Mars. Using time-dependent geodynamical and atmospheric models, I will show results on how (1) geodynamically produced hydrogen and methane via serpentinization generates a flux of reducing elements within the lithosphere and (2) how oxygen-rich oases can be formed on the surface and in the crust as a result of brine-atmosphere interactions. This allows us to study the ability of planets, like Earth and Mars, to generate nutrient-rich and redox-rich oases as a function of planet mass, composition, age, and tectonic mode. Moreover, our model also opens the doors to make predictions where and when such oases could have existed or could still exist on Mars. The latter does not only help to better understand how Mars evolved but can become a promising tool to help guide future landing site selections and even manned missions that are looking for hydrogen-rich and oxygen-rich reservoirs on the red planet.
Searching for Life on Mars: Consensus Input from the Mars Exploration Community
Lindsay Hays, JPL/Caltech; Jennifer L. Eigenbrode, NASA Goddard Space Flight Center; Sarah Stewart Johnson, Georgetown University; Tori Hoehler, NASA ARC; David Des Marais, NASA ARC; Lindsay Hays, JPL/Caltech; David Beaty, JPL/Caltech; and Victoria E. Hamilton, Southwest Research Institute
The Mars Exploration Program Analysis Group’s (MEPAG’s) “Goals Document” is regularly updated to reflect the exploration community’s consensus regarding its scientific priorities for robotic investigations at Mars.
Goal I—to determine if Mars ever supported life—is one of four unprioritized goals and has been a key driver of the Mars Exploration Program. Goal I is broken down into two objectives that focus on searching for evidence of past (objective A) and extant life (objective B), which are kept separate because there are significant differences in the strategies, technologies, target environments, and forms of evidence involved in those searches. For both objectives, “A clear scientific strategy (i.e., an investigative plan built on target-specific hypotheses and measurements) can only be formulated once an environmental record or environment is understood in sufficient detail” (MEPAG goals document, 2015). Although the prioritization and definition of the Goal I objectives, sub-objectives, and investigations are subject to change in response to mission discoveries and community discussions, priority is currently placed on objective A (evidence for past life), because previous mission observations have largely provided details on past environmental conditions.
Objectives A and B are further broken down into sub-objectives focused on (1) identification of habitable environments (past or present) and characterization of the conditions and processes that may have influenced the degree or nature of habitability therein, (2) assessing the potential of specific conditions and processes that may influence the expression and/or degradation of signatures of life and habitability, and identify favorable deposits for their detection, and (3) determining if biosignatures of a prior or extant ecosystem are present. Finally, each sub-objective lists investigations that would collectively enable the achievement of the sub-objective while avoiding discussion of implementation.
The NASA Exoplanet Exploration Program
Douglas Hudgins and John Gagosian, NASA HQ, and Gary Blackwood, JPL
The NASA Exoplanet Exploration Program (ExEP) is chartered to implement the NASA space science goals of detecting and characterizing exoplanets and to search for signs of life. The ExEP manages space missions, future studies, technology investments, and ground-based science that either enables future missions or completes mission science. The exoplanet science community is engaged by the program through science definition teams and through the Exoplanet Program Analysis Group. The ExEP includes the space science missions of Kepler, K2, and the proposed WFIRST-AFTA, which includes dark energy science, a widefield infrared survey, a microlensing survey for outer-exoplanet demographics, and a coronagraph for direct imaging of cool outer gas- and ice-giants around nearby stars. Studies of probe-scale (medium-class) missions for a coronagraph (internal occulter) and starshade (external occulter) explore the trades of cost and science and provide motivation for a technology investment program to enable consideration of missions at the next decadal survey for NASA Astrophysics. Program elements include follow-up observations using the Keck Observatory, which contribute to the science yield of Kepler and K2, and include mid-infrared observations of exo-zodiacal dust by the Large Binocular Telescope Interferometer, which provide parameters critical to the design and predicted science yield of the next generation of direct imaging missions. ExEP includes the NASA Exoplanet Science Institute, which provides archives, tools, and professional education for the exoplanet community. Each of these program elements contribute to the goal of detecting and characterizing Earth-like planets orbiting other stars and seeks to respond to rapid evolution in this discovery-driven field and to ongoing programmatic challenges through engagement of the scientific and technical communities.
Subsurface Mars as the Longest Continually Available Habitat: Implications for the Search for Life
Bethany Ehlmann, California Institute of Technology
The last decade of Mars exploration has revealed a dozen aqueous, potentially habitable environments, ranging from lacustrine to hydrothermal to weathering. These environments varied in space and time and imply a warm and wet subsurface with punctuated periods of more clement conditions that allowed liquid water at a cold surface. Mineralogical evidence for past liquid water is widespread, but lack of evidence for terrestrial-style, open-system chemical weathering in most terrains points to subsurface water-rock interactions, water-limited weathering under
cold conditions, or both (Hurowitz and McLennan, 2007; Ehlmann et al., 2011; McLennan et al., 2014; Arvidson et al., 2014), supported by climate models (Wordsworth et al., 2015).
Searches for martian life must be informed by these conditions, different from those of early Earth. Unlike on Earth, little geologic evidence exists for a martian northern ocean or individual lakes that persisted continuously as stable habitats for billions of years. Instead, Mars may have episodically hosted a northern ocean (Pan et al., 2017), and in the southern highlands, lakes, and rivers fed by runoff from ice melt or precipitation were episodic (10 kyr to 10 Myr; Barnhart et al., 2009; Grotzinger et al., 2015). Second, Mars lost its magnetic field early (3.9-4.1 Ga) and also likely had a thin atmosphere (<1 bar) by the time periods accessible in rock strata (Ehlmann et al., 2016). Consequently, martian organisms dealing with challenges of cold and surface aridity also faced surface radiation doses many times higher than on Earth. Thus, martian surface habitats have always been more episodic and more extreme than age-equivalent surface habitats on Earth. Consequently, rock-hosted habitats, shielded from radiation and showing evidence of persistent water, warrant particular attention in the search for life: groundwater aquifers, hydrothermal systems, and weathering profiles. Here we describe habitats for past and present rock-hosted Mars life and potential biosignatures. Similarly, data for liquid water on modern Mars point to the importance of the subsurface. Salts excavated in soils by the Spirit rover and climate data coupled with perchlorate detections by Curiosity show likely brine creation and brief stability a few to tens of cm beneath the surface (Wang et al., 2006; Arvidson et al., 2008; Martin-Torres et al., 2015). Recurring slope lineae show temperature-correlated activity consistent with a role for liquid water or salt deliquescence (McEwen et al., 2011; Stillman et al., 2014) but a dry surface (Edwards and Piquex, 2016).
Social and Conceptual Issues in Astrobiology
Kelly Smith, Clemson University
A very successful off-year workshop of the International Society for the History, Philosophy and Social Studies of Biology (http://kcs098.wixsite.com/socia) was held at Clemson University in September to explore the social and conceptual issues surrounding astrobiology. The workshop mixed younger scholars and graduate students with established scholars from a wide variety of disciplines, including history, philosophy, communications, biology, astronomy, engineering, theology, medicine, chemistry, geology, and education.
Such a diverse group of researchers produced an equally diverse set of presentations, both in terms of focus and approach. But they fell into five broad categories: (1) philosophy of science (e.g., evidentiary considerations and the risks of anthropocentrism), (2) intelligence/consciousness (e.g., the evolution of cognitive capacity and conceptual difficulties for communication), (3) life concepts (e.g., universality in biology versus conceptual pluralism), (4) ethical issues (e.g., planetary protection policies and extraterrestrial wilderness), and (5) social/cultural issues (e.g., the interplay between astrobiology, religion, education, and politics). The quality of presentations was excellent, and many will appear in a forthcoming conference volume.
The organizers plan to leverage the success of this first meeting with a second meeting at the University of Nevada, Reno in the spring of 2018, with the ultimate goal of founding a new society dedicated to scholarship and outreach on these exciting issues.
IN SITU BIOSIGNATURES
Resilience of Molecular Biosignatures under Simulated and Analogue Planetary Environments
Douglas Galante, Brazilian Synchrotron Light Laboratory (LNLS/CNPEM); Fabio Rodrigues, Instituto de Química da Universidade de São Paulo; and Tamires Gallo, Maria Fernanda Cerini, and Nathalie Rivas, LNLS/CNPEM)
This work will present an overview of the resilience of biomolecules that could be used as indicative of the past or present presence of life on exposed planetary surfaces, such as that of Mars or the icy moons of the solar system.
Different classes of molecules have been used, but especially biological pigments—carotenoids, chlorophyll, and porphyrins. These have been tested in laboratory under simulated conditions, especially radiation, pressure and temperature, and the response has been measured using in situ and ex situ spectroscopic methods—UV-Vis, Raman, and Fourier transform infrared spectroscopy. The molecules have also been exposed to the stratospheric environment using balloons, to produce a more complete martian analogue environment.
Life Detection in Planetary Analog Materials: Applications to the Search for Life in the Solar System
Rosalba Bonaccorsi, SETI Institute/NASA ARC; Christopher McKay, NASA ARC; Alfonso Davila, SETI Institute/NASA ARC; and David Willson, Keck Institute of Space Studies/NASA ARC
Detection of molecular proxies for life in planetary environments depends on four conditions: (1) their initial presence due to current and past biological production, (2) their concentration in measurable amount through sedimentary processes in geological materials, (3) their long-term preservation within the material, and (4) the analytical ability of payload instruments to detect and identify them. The analytical requirement is a very key one. False negatives (null or incomplete recovery) can result from the analysis of both biologically lean and biologically rich environmental samples. To test effectiveness of life-detection assays, we have analyzed lipopolysaccaride (LPS) Lipid A and Adenosin Triphosphate (ATP) biomarkers in a variety of planetary-like environments (e.g., hypersaline lakes, fine-grained clay-rich sediments, ice-cemented ground, cyanobacteria-colonized soil crust, and hydrothermal sinters). We present here results from the in situ analysis of Lipid A and ATP using lab-on-the chip/ wet chemistry assays. In geological and water samples, LPS- and ATP-based biomass range from 102 to 109 cells/ gram. Most importantly, LPS and ATP detection can be affected by the mineralogical (i.e., clay minerals, nanophase iron oxyhydroxides) and physico-chemical composition (salts, pH, T, organics) of the geological matrix. Failing to detect life in modern terrestrial environments that we know have abundant life is a chief concern for our ability to detect life on Earth and other planets as well. Learning how to assess and mitigate matrix-related interference is key to the success of future life detection missions to our solar system, including Mars and the ocean world icy moons, Enceladus and Europa.
Biosignatures of a Hyper Saline Environment
Heather Smith, Keck Institute of Space Studies Institute of Practical Robotics
We report on changes in the salt crust photosynthetic microbial community measured when exposed to 1 week of simulated martian conditions (UV, pressure, and temperature) in a Mars chamber. Halophile ecosystems are models for life in extreme environments including planetary surfaces. Our research was on the microbial preservation potential of salt subjected to martian pressure, UV, and temperature. Figure 1 is a picture of the research site with the inset showing the microbial stratigraphy within the salt crust. Visual changes within the stratigraphic layering and phospholipid fatty acid (PLFA) analysis were used to determine changes in microbial community.
Linking Microbial Communities to Preserved Biosignatures
Scott Perl, NASA/JPL and USC; P. A. Vaishampayan, Caltech/JPL; F. A. Corsetti, USC; O. Piazza, USC; K. W. Williford, Caltech/JPL); M. L. Tuite, Caltech/JPL; B. K. Baxter, Westminster College; J. Butler, Westminster College; W. M. Berelson, USC; and K. H. Nealson, USC
Determination of potential in situ biology in the martian subsurface in the form of biosignatures and/or biomarkers can be extremely difficult to detect due to their likely physical location embedded within mineralogy and sedimentary outcrops. References to terrestrial extreme environments that have similar geologic, geochemical, and aqueous histories are necessary to distinguish between abiotic and biotic samples (not from and from organic life, respectively). The precipitation of evaporate minerals from ancient and receding lakebeds allows for evidence
of in situ biogenic material to be preserved and/or recorded in the structure of minerals that use the evaporating lakebeds as input fluids for evaporate formation. The depth of preserved biotic information from the perspective of a rover’s payload can be complemented by independent microbiological analysis. These complementary analyses would behoove future planetary rovers that have mineralogical and organic detection instruments due to comparisons that can be made from the mineralogy at the elemental level and biogenically with DNA extraction and sequencing as well as fatty acid extraction. This would help confine the types of organics that a planetary rover could discover in situ while providing biological evidence that a rover’s toolset cannot currently achieve. The purpose of this investigation is to classify, validate, and quantify organics (archaea and bacteria) that have been preserved within mineralogy, formed in situ, from the evaporation of saline lake waters. The methodology focuses on entombed biology within evaporates employing two principal initiatives that support microbiology laboratory experiments and rover instrument quantification.
Sulfur Redox States among High Arctic Sites and Carbonaceous Chondrites
Ted K. Raab, Carnegie Institution for Science; Darren Locke, Jacobs/NASA Johnson Space Center; and Trudy Bolin, University of Illinois, Chicago
Biochemical energy can be generated through transformation of redox states. On Earth, such elements include Fe, S, Mn, Cl, and Cu. In the hazardous radiation environment of space, life requires shielding from charged particles and intense UV. In a series of field and laboratory experiments, we explore the “niche space” for sulfur transformations among bacteria and viruses—an element with the largest number of accessible redox states. We also identify pore networks within carbonaceous chondrites meteorites. Both questions rely on X-ray methods that can eventually be developed for unmanned exploration.
It’s Alive! (But Is It Local?) Planetary Protection Considerations in Distinguishing Extraterrestrial Life from Earthly Contamination
John Rummel, SETI Institute
While much can be made of the search for in situ biosignatures representing either life as we know it, or life as we don’t know it, the spectre of detecting life from Earth when looking for life from (name your favorite extraterrestrial habitat) haunts the field. Earth life, in its profusion, has made it difficult to “see” extraterrestrial life unless strict measures are taken to avoid and/or remove the biological and organic contamination affecting spacecraft carrying life-detection instrumentation. Given the challenges associated with reaching potential life-sites on other worlds and the revival of interest in novel techniques to detect life in samples that can be held in a robotic “hand,” the planetary protection measures designed to protect against false indications of life on planetary bodies may seem daunting. Nonetheless, searching for life while distributing contamination widely into the surrounding environment is both counterproductive and, for most spacefaring nations, illegal in their adherence to the United Nations Outer Space Treaty, res ipsa loquitur. Even more obviously, false-positive results about life in a particular location can have the unfortunate result of drowning out the actual detections of extraterrestrial life that the taxpayers are funding and that we are pursuing with our own lives. This presentation will discuss the current status of planetary protection measures available to prevent Earth contamination of spacecraft searching for extraterrestrial life.
Ammonium in Clays—A Biosignature
Eva Stueeken, University of California, Riverside, and University of Washington, Seattle
Some of the oldest rocks on Earth—3.8 billion-year-old metasediments from Isua—contain significant amounts of nitrogen with concentrations of several hundred parts per million. Such concentrations are commonly found in
younger mudrocks, where they are usually thought to be derived from the degradation of biomass and incorporation of NH4+ into clay minerals. Whether or not an abiotic nitrogen cycle could mimic such high concentrations is so far unknown. This question is addressed with a numerical box model that simulates an abiotic nitrogen cycle with inputs of fixed nitrogen through lightning, impacts, and hydrothermal activity. Abiotic sinks include volatilization of NH3 back into the atmosphere and adsorption of NH4+ on mineral surfaces. The results suggest that abiotic pathways are unlikely to produce nitrogen concentrations greater than a few parts per million under realistic pH conditions and source fluxes. The observed abundances are thus most plausibly interpreted as a relic of an early Archean biosphere. In conclusion, nitrogen concentrations may serve as a useful biosignature on other planets.
Signs of Life 2002
David Smith, National Academies of Sciences, Engineering, and Medicine
In April 2000, the National Academies’ Space Studies Board and Board on Life Sciences jointly organized a workshop to discuss a variety of topics, including the following: the search for extraterrestrial life in situ and in the laboratory; extant life and the signature of extinct life; and determination of the point of origin (terrestrial or not) of detected organisms. The material presented during the workshop and in follow-on study were published in the 2002 report Signs of Life.
The report was organized around four general questions. First, how does one determine if living terrestrial organisms are on a spacecraft before launch? Second, how does one determine if there are living organisms in a returned sample? Third, how does one determine if living organisms have been present at some earlier epoch and have left fossil remnants behind in a returned sample? Fourth, how does one determine whether there are living organisms or fossils in samples examined robotically on another solar system body?
Significant progress has been made in the last 16 years in addressing many of the questions above. Indeed, much of the material contained in Signs of Life might now be considered dated. However, the report’s concluding chapter contained two very useful tables summarizing life-detection techniques that were promising at the time and gave assessments of their likely sensitivities and areas of applicability. These tables are reproduced in the current poster and are available online at the National Academies Space Studies Board website. 2016 workshop participants are encouraged to review specific entries and suggest updates and/or other amendments, as appropriate.
NASA’s Life Detection Ladder 2016
David Smith, National Academies of Sciences, Engineering, and Medicine
The direct detection of extant life has not been attempted by NASA since the Viking missions in the late 1970s. NASA’s Ladder of Life Detection (http://astrobiology.nasa.gov/research/life-detection) was generated to stimulate and support discussions among scientists and engineers about how one would detect extant life beyond Earth but within the solar system (particularly on Europa and the other “ocean worlds”). In creating the Ladder, we started with the NASA definition of life, “Life is a self-sustaining chemical system capable of Darwinian evolution” and considered the specific features of the one life we know—terran life. Please e-mail any suggestions to firstname.lastname@example.org.
The 2007 Astrobiology Strategy for the Exploration of Mars
David Smith, National Academies of Sciences, Engineering, and Medicine, and Bruce Jakosky, Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder
The last decade of the 20th century and the first decade of the 21st witnessed a rebirth in interest in the exploration of, and search for life on, Mars and a spate of new spacecraft missions. Mars Pathfinder, Mars Odyssey, Mars Express, Mars Reconnaissance Orbiter, and the Mars Exploration rovers Spirit and Opportunity provided a wealth
of new information about the planet’s environment, including strong evidence of a watery past and the possible discovery of atmospheric methane. In addition, new developments in our understanding of life in extreme conditions on Earth suggest the possibility of microbial viability in the harsh martian environment. Together, these results have greatly increased interest in the search for life on Mars, both within the scientific community and beyond. Given the enhanced scientific and political interest in the search for life on Mars, it is surprising that NASA’s then most recent end-to-end strategy for the detection of martian life, contained in the report An Exobiological Strategy for Mars Exploration, was published as long ago as 1995.
Against this backdrop, NASA’s Science Mission Directorate requested that the Space Studies Board develop an up-to-date integrated astrobiology strategy for Mars exploration that brings together all the threads of this diverse topic into a single source for science mission planning. The resulting report, An Astrobiology Strategy for the Exploration of Mars, published in 2007, addressed the following topics:
- The characteristics of potential targets for Mars exploration particularly suited for elucidating the prebiotic and possibly biotic history of Mars, and methods for identifying these targets;
- A catalog of biosignatures that reflect fundamental and universal characteristics of life (i.e., not limited to an Earth-centric perspective);
- Research activities that would improve exploration methodology and instrumentation capabilities to enhance the chances of astrobiological discovery; and
- Approaches to the exploration of Mars that would maximize the astrobiological science return.
Biosignatures of Extant Life on Ocean Worlds (BELOW) Workshop
Jennifer Eigenbrode, NASA GSFC; Stephanie Getty, NASA GSFC; Tori Hoeler, NASA ARC; John Priscu, Montana State University; Andrew Steele, Carnegie Institution of Science; and the Working Group Chairs of BELOW
The aim of BELOW was to evolve our understanding of the detectability of extant life on ocean worlds, such as Europa and Enceladus. The event brought together astrobiologists, biologists, chemists, geologists, oceanographers, and mission and instrument developers to discuss the informational value of different types of biosignatures, the importance of context and the concept of ecology in the search for extant life, and as well as exploration criteria that would support a productive search for extant biology in future missions. The workshop successfully identified signals deemed important for the search for life on ocean worlds as well as issues of noise and processing concerns. A summary of the results of the workshop will be presented.
A Probabilistic Intrinsically Calibrated Framework for Recognizing Complex Molecules as Biosignatures
Jennifer Eigenbrode, NASA GSFC, and Lee Cronin, University of Glasgow
The ability of living systems to replicate and evolve allows for the generation of complex molecules, such as metabolites and co-factors, which would be highly unlikely to form in any significant quantity in the absence of biology. We have developed an intrinsic general complexity measure that can predict the likelihood of a molecule (and by extension complex polymers) to have formed by a non-biological process, that can be assessed using analytical methods. By comparing the complexity of simple molecules to that of complex ones (found in biology), we aim to establish a threshold beyond which the molecules are increasingly unlikely to form without supporting biological machinery. Then by evaluating the complexity of unknown molecules found in a given environment, we use the threshold to assign the probability that the molecules in question were generated by a living system, either directly as a metabolite, or indirectly by a person or robot. The advantage in searching for complexity, rather than specific chemical features, is that it is completely general and agnostic to the specific chemical or biological details.
Detecting Motility and Morphology as Biosignatures
Chris Lindensmith, JPL; Jay Nadeau, Caltech; Manuel Bedrossian, Caltech; Marwan Elkholy, McGill University; Jody Deming, University of Washington; and Max Showalter, University of Washington
Meaningful activity (motility, cell division, biofilm formation) is an unambiguous biosignature. Because life in the solar system is most likely to be microbial, the question is whether activity may be detected effectively on the micrometer scale, and whether inactive or dormant organisms may be stimulated to become active. Recent results on microbial motility in oligotrophic Earth environments, such as the open ocean, have provided insight into the physics and biology that determine whether and how microorganisms as small as bacteria and archaea swim, under which conditions, and at which speeds. These discoveries are only starting to be reviewed in an astrobiological context. This poster discusses these findings in the context of Earth analog environments and environments expected to be encountered in the outer solar system, particularly the Jovian and Saturnian moons. We present several imaging technologies, including holographic and Fourier ptychographic microscopy capable of observing activity of sub-micrometer-sized organisms, and discuss how an instrument would interface with several types of sample-collection strategies and with chemical biosignature detection.
Capillary Electrophoresis Separations of Chiral Amino Acids for Biosignature Detection
Jessica Creamer, Maria F. Mora, and Peter A. Willis, JPL
Amino acids are fundamental building blocks of terrestrial life as well as ubiquitous byproducts of abiotic reactions. In order to distinguish between amino acids formed by abiotic versus biotic processes, it is possible to use chemical distributions to identify patterns unique to life. This article describes two capillary electrophoresis methods capable of resolving 17 amino acids found in high abundance in both biotic and abiotic samples (seven enantiomer pairs D/L-Ala, -Asp, -Glu, -His, -Leu, -Ser, -Val, and the three achiral amino acids Gly, β-Ala, and GABA). To resolve the 13 neutral amino acids, one method utilizes a background electrolyte containing γ-cyclodextrin and sodium taurocholate micelles. The acidic amino acid enantiomers were resolved with γ-cyclodextrin alone. These methods allow detection limits down to 5 nM for the neutral amino acids and 500 nM for acidic amino acids and were validated by analyzing samples collected from Mono Lake with minimal sample preparation.
Biosignatures from a Deep Biosphere: Lessons Learning from Earth
Haley Sapers, Caltech; Jan Amend, USC; David Beaty, JPL; Rohit Bhartia, JPL; Kevin Cannon, Brown University; Charles Cockell, University of Edinburgh; Max Coleman, JPL; Dave Des Marais, NASA ARC; J. Marlow, Harvard; B. Ehlmann, Caltech; Tori Hoehler, NASA ARC; Tom McCollom, University of Colorado; Joe Michalski, Planetary Science Institute; John Mustard, Brown University; Ken Nealson, USC; Paul Niles, NASA Johnson Space Center; G. R. Osinski, Western University; Tullis Onstott, Princeton University; Victoria Orphan, Caltech; Barbara Sherwood-Lollar, University of Toronto; Alexis Templeton, University of Colorado; Greg Wanger, JPL
Introduction: The current surface conditions on Mars are incompatible with life as we know it: the surface atmospheric pressure precludes standing water. Harsh UV and gamma radiation destroy complex organic molecules in the surface and near-surface environment, hindering detection of organic biosignatures. These harsh surface conditions potentially extended to the Noachian/Hesperian boundary, so surface environments, including lakes/ deltas, may not have habitable at the surface. However, subsurface refugia may have extended the window of habitability, and putative subsurface pockets of habitable conditions could potentially still harbor extant life and their biosignatures. Understanding the biological processes in the terrestrial subsurface will yield insight into the identification, detection, and characterization of potential subsurface martian biosignatures.
Subsurface habitats on Earth: The minimum requirements for subsurface life include space, carbon, and energy linked in a substrate allowing for an adequate supply of nutrients and removal of toxic waste products. Subsurface environments may harbor the majority of microbial life on Earth and Archaean biosignatures suggest the existence of a terrestrial biosphere for billions of years. Recent findings from multiple sulfur isotope investigations of fracture waters in 2.7 Ga rock from the Canadian Shield demonstrate the potential for isotopic evidence of subsurface microbial activity to be preserved on long geologic timescales. Subsurface microbial communities are sustained through chemolithoautotrophic metabolic processes adapted to energy limitations limited by the geothermal gradient reaching the upper temperature limits of life. Extant subsurface metabolisms in these terrestrial Mars analogue habitats include coupling oxidation of H2 generated by serpentinization reactions to reduction of oxidized iron and sulphate minerals. The dynamic biogeochemical reactions defining life processes in the subsurface constantly process abiotic materials resulting in biosignatures with the potential to be preserved in the rock record. Understanding the biologically mediated processes that result in geological biosignatures not only extends our knowledge of the limits of life on Earth, but provides a framework with which to search for life on Mars.
In Situ Resource Utilization for Environmental Protection
Yu Qiao and Brian J. Chow, University of California, San Diego
As searching for life on Mars draws increasing attention, environmental protection associated with unmanned and manned space exploration missions must be carefully investigated. One major technical issue is the lack of infrastructural materials to build relatively large-scale insulation layers, protective walls, separation zones, permanent waste-disposal containers, and sealed storage units, among others. In a recent experimental research, we discovered that both primordial and secondary martian soils could be directly compacted into strong and dense “bricks,” with appropriate processing conditions. The compaction procedure was simple, fast, and more importantly, energy efficient. It was conducted under ambient condition; no heating/calcination or any additives was involved. This technique may also have important relevance to expansion and maintenance of martian bases/ outposts/habitats, as well as massive and bulky parts in space research facilities and equipment, such as launch/ landing platforms and supports of space telescopes.
Ocean Biomolecule Explorer for Astrobiology
Heather Smith, Keck Institute of Space Studies Institute of Practical Robotics; Andrew Duncan, Desert Sensors; and Chris Lloyd, Retego Labs
The Ocean Biomolecule Experiments for Astrobiology is a life detection instrument suite designed towards an Ocean Worlds surface mission. The instrument suite relies on the modification of commercial off-the-shelf instruments combined with newly developed biochemical analysis methods to paint a picture of the biological realm on Europa’s Ocean World. This search for extant life relies on our understanding and assumptions of Europa, Enceladus, and Titan within the context of Earth’s biochemistry and known metabolic process. To gain an initial picture of Europa life, if present, the instrument suite is designed to detect a range of targets associated with life on Earth, including basic biomolecules as well as the yield from complex metabolic process. The instrument suite will both detect the presence of extant life and provide insight into evolutionary process on the Ocean World. While the instrument suite in this proposal is designed for a Europa lander, the fundamental method of detection could also be applied to Enceladus and Titan. As such, when relevant, a brief analysis on the modification of the instruments for Enceladus and Titan is also included.
Non-Contact Detection of Biomolecules
Andrew Duncan, DesertSensors; Heather Smith, Keck Institute of Space Studies Institute of Practical Robotics; and Chris Lloyd, Retego Labs
For this project, we designed an instrument to detect bacteria via biomolecular (amino acids, metabolites) fluorescence. We proposed a novel technique for searching for direct evidence of life on planetary bodies. Fluorescence laboratory measurements using the portable instrument reveal microbial concentration in desert soil to range from 102 to 107 bacteria per gram of soil equivalent. Biomolecules and polycyclic aromatic hydrocarbons are highly fluorescent at wavelengths in the ultraviolet (266 nm, 355 nm), but not as much in the visible 532 nm range. Preliminary results show minerals discovered, such as perchlorate, fluoresce highest when excited by 355 nm light. Overall, we conclude the fluorescent instrument described is suitable to detect microbes, organics, biomolecules, and some minerals via fluorescence, offering a high scientific return for minimal cost with non-contact applications in extreme environments on Earth and on future planetary missions.
Accelerating Our Search for Life Beyond Earth with Privately Funded Robotic Space Missions
Jon Morse, BoldlyGo Institute
Basic research in the space sciences holds essentially limitless potential for tackling profound questions of our existence and opening the doors of exploration, innovation and future economic opportunity. The search for life beyond Earth is a particularly compelling endeavor that is attracting significant private funding. The BoldlyGo Institute seeks to conduct privately funded, world-class space science missions that would tangibly accelerate our search for extraterrestrial life, feeding forward scientifically and technologically to future missions. BoldlyGo’s initial portfolio includes a Mars robotic dust sample return mission and a UV-visible space telescope for the post-Hubble era that could host a coronagraph and be paired with a starshade. We describe the mission plans and the opportunities that such missions could provide in filling funding-driven gaps in the space science portfolio.
iSEE: In-Situ Spectroscopic Europa Explorer
Pablo Sobron, SETI Institute
The in-situ Spectroscopic Europa Explorer (iSEE) is a next-generation ultra-compact Raman Spectrometer with superior performance that meets the top-level scientific requirements of the 2022 Europa lander mission. Our motivation is to build a small, versatile instrument that can address priority science goals in different spacecraft configurations (orbiters, flybys, landers, rovers). iSEE utilizes an innovative combination of light source, adaptive spatial coding optics, and detector. It integrates a high-performance signal processor and data processing algorithms that enable unprecedented measurements: in situ chemical identification and quantitation of complex organic compounds, including pre-biotic compounds (e.g. amino acids), biomolecules (organic biomarkers including proteins, lipids, and nucleic acid polymers), minerals, and volatiles. iSEE also provides sample context, including ice composition, crystallinity, and ice phase distribution. iSEE has potential to become a critical new instrument in NASA’s exploration toolbox that can replace already-flown in-situ sensing technologies in future mission opportunities. It will deliver three game-changing advantages: (a) unprecedented Raman analytical capabilities—on-spectrometer quantitative analysis of organic content, minerals, and volatiles at or <1 ppb; (b) minimization of the cost and complexity of the light source system; and (c) possibility for novel mission architectures—organic, mineral, volatile analysis, and sample context, are offered within a single, ultra-compact instrument. The following missions highlighted by the Planetary Science Directorate will specifically benefit from iSEE: (a) landed exploration missions to Venus, the Moon, Mars, Europa, Titan, comets, and asteroids and (b) sample return missions to the Moon, Mars, comets and asteroids. In addition, iSEE may be used to identify and map available planetary in situ resources and to spur the development of autonomous in-situ resource utilization devices for robotic and human missions.
MapX: An In Situ, Full-Frame X-ray Spectroscopic Imager for the Biogenic Elements
Dave Blake, Exobiology Branch/NASA ARC; Philippe Sarrazin, SETI; Kathy Thompson, SETI; and Thomas Bristow, NASA
Microbial life exploits microscale disequilibria at boundaries where valence, chemical potential, pH, Eh, etc. vary on a length scale commensurate with the organisms themselves—tens to hundreds of micrometers. These disequilibria can exist within cracks or veins in rocks and ice, at inter- or intra-crystalline boundaries, at sediment/ water or sediment/atmosphere interfaces, or even within fluid inclusions trapped inside minerals. The detection of accumulations of the biogenic elements C, N, O, P, and S at appropriate concentrations on or in a mineral/ice substrate would constitute permissive evidence of extant life, but context is also required. Does the putative biosignature exist in a habitable environment? Under what conditions of pressure, temperature, and chemical potential was the host mineralogy formed? MapX is an arm-deployed contact instrument that directly images the biogenic elements C, N, O, P, and S, as well as the cations of the rock-forming minerals (Na, Mg, Al, Si, K, Ca, Ti, Cr, Mn, and Fe) and important anions such as Cl and Fl. The instrument provides element images having ≤100 µm lateral spatial resolution over a 2.5 cm by 2.5 cm area, as well as quantitative XRF spectra from ground-selected or instrument-selected Regions of Interest (ROI) on the sample. Quantitative XRF spectra from ROI can be translated into mineralogies using ground- or instrument-based algorithms. Either an X-ray tube source (X-ray fluorescence) or a radioisotope source such as 244-Cm (α-particle and γ-ray fluorescence) can be used, and characteristic X-rays emitted from the sample are imaged onto an X-ray sensitive charge-coupled device through an X-ray MicroPore Optic. As a fluorescent source, 244-Cm is highly desirable in a MapX instrument intended for life detection since high-energy α-particles are unrivaled in fluorescence yield for the low-Z elements. The MapX design as well as baseline performance requirements for a MapX instrument intended for life detection/identification of habitable environments will be presented.
Curation of Deep Space Samples in Transit
Madhu Thangavelu, University of Southern California
Samples retrieved from deep space (e.g. asteroid or comet) by virtue of trajectories and energies required to bring them back to Earth, can take many months to years to reach Earth. During that period, changes can occur to those samples. Curation procedures are sought that can preserve the sample in as pristine of a condition as possible. Some ideas and recommendations are proposed.
Astrobionibbler: In Situ Microfluidic Subcritical Water Extraction
Aaron Noell, JPL; Anita M. Fisher, JPL; Nobuyuki Takano, JPL; Kisa Fors-Francis, Oklahoma State University; Stewart Sherrit, JPL; and Frank Grunthaner, JPL (retired)
Searching for trace levels of organic molecules on Mars or other rocky bodies is a formidable challenge, but impressive capabilities are being developed for reducing instrument size without losing performance for techniques such as gas chromatography with mass spectrometric detection or capillary electrophoresis with laser induced fluorescence detection. However, less work has been done to develop suitable instrumentation for analyte extraction and extract delivery to these analytical instruments. On Mars, the main driver for new extraction techniques is the difficulty that both the Viking Landers and Curiosity Rover have experienced with pyrolysis of samples; where degradation of the indigenous organics has occurred because of the high temperature breakdown and subsequent reactions of perchlorate salts.
The Astrobionibbler instrument (ABN) focuses on this problem, with the primary aim of developing a chip based fluidic device for subcritical water extraction (SCWE) from powder samples. In SCWE a pressurized system allows water to remain liquid at temperatures greater than 100°C (but less than the critical point at 374°C) and
perform accelerated extractions on a variety of samples. The high temperature allows water to behave like other less polar solvents because the dielectric constant of water changes dramatically with temperature. This enables molecular class targeted extractions based on polarity, a useful feature when trying to eliminate unwanted interferences for downstream instruments. The high temperatures reached in SCWE can also be used to hydrolyze biopolymers such as proteins into their constituent amino acids, increasing our ability to separate and conclusively detect potentially very small amounts of material. The work described here will focus on the development of the chip based ABN instrument, and tests performed on amino acid/protein extraction/hydrolysis.
In-Situ Liquid Extraction and Analysis Platform for Mars and Ocean Worlds
Florian Kehl, D. Wu, M.F. Mora, J.S. Creamer, and P.A. Willis, JPL
Mars, Europa, Enceladus, and Titan are the most auspicious worlds to search for signatures of past or present alien life in our solar system. Here we present a compact, integrated sample extractor and analysis unit that could be used to support robotic missions seeking these chemical signatures of life. This wet chemistry instrument addresses habitability and the potential to preserve biosignatures by characterizing the local geochemical environment. In a first step, inorganic and putative organic compounds are automatically extracted from 1 cm3 of regolith or ice/soil mixtures by subcritical water extraction at 175°C to 200°C and elevated pressures. Inline, miniaturized electrochemical probes quantify the eluate’s pH, redox potential and electrical conductivity to better understand the ice or soil chemistry and mineralogy. Colorimetric measurements by flow injection analysis in a fully integrated mesofluidic manifold furthermore allow additional assessment of the soil’s ionic composition. Besides the evaluation of the potential for past or present biology, this system can be employed as a front-end instrument for subsequent, more sophisticated organic analyzers, such as capillary electrophoresis or mass spectrometer units, to put these down-stream measurements in context.
Capillary Electrophoresis Instrumentation for Determination of Chemical Distributions Indicative of Life on Future Spaceflight Missions
Maria Mora, JPL/Caltech; F. Kehl, JPL; E. Tavares da Costa, JPL; J. Creamer, JPL; J. Chapman, SCIEX; D. Arnold, SCIEX; T. Horton, SCIEX; M. Darrach, JPL; A. Ricco; and P.A. Willis, JPL
The search for evidence of life beyond Earth is among the highest-level goals in planetary exploration. However, despite multiple orbiter and landed missions to extraterrestrial bodies in the solar system, we still haven’t found evidence of life. A powerful approach in the search for life involves seeking biochemical signatures of life at the molecular level, as distributions of organic molecules. The liquid-based separation techniques capillary electrophoresis (CE) and its miniaturized version, microchip electrophoresis (ME) overcome the limitations of gas-phase techniques and hold unique promise in the search for signatures of life on other worlds. Although multiple detection methods can be coupled to CE and ME, we focused on the two most powerful organic detection and characterization techniques: mass spectrometry (MS) and laser-induced fluorescence (LIF). LIF offers the highest sensitivity to organics, while MS allows complete identification. These techniques are complementary of each other and would allow full characterization of a sample in situ. Here we describe the status of instrumentation developed at JPL and the steps we are taking to someday enable its implementation on other worlds.
We describe a ME-LIF system we dub “The Chemical Laptop,” which would provide the sample-processing capabilities required for in situ analysis with sub parts-per-billion sensitivity in a compact, low-mass, and low-power package. This instrument concept could be adapted to a variety of astrobiologically interesting targets like Europa, Enceladus, or Titan. This instrument is the first battery-powered and truly portable “end-to-end” ME-LIF astrobiology instrument capable of receiving an unlabeled liquid sample and performing all operations required for analysis.
We also present here the Organic Capillary Electrophoresis Analysis System (OCEANS) that couples capillary electrophoresis with electrospray ionization mass spectrometry (CESI-MS), in order to enable the characterization of distributions of organic compounds on future in situ planetary missions to ocean worlds.
The Search for Life with a Large Segmented-Aperture Space Telescope
Christopher Stark, Neil T. Zimmerman, Mamadou N’Diaye, Kathryn St. Laurent, Rémi Soummer, Laurent Pueyo, Anand Sivaramakrishnan, and Marshall Perrin, Space Telescope Science Institute (STScI), and Robert Vanderbei, Princeton University
The search for life on extrasolar planets requires the ability to detect and spectrally characterize planets 10 billion times fainter than their host stars. These measurements will likely be performed, at least in part, using a coronagraph to block stellar light. Historically, coronagraphs have been thought to perform at an acceptable level only with geometrically simple monolithic apertures, limiting the telescope diameter to roughly <4 m. Here I present a number of fundamental reasons why the search for life may require larger segmented apertures, ~12 m or greater, and show that new coronagraph designs may enable adequate performance for a large range of segmentation patterns.
Sample Preparation Enabling Characterization of In Situ Biosignatures
Kathleen Craft, Christopher Bradburne, Matthew Hagedon, Jason Tiffany, and Matthew Grey, Johns Hopkins University Applied Physics Laboratory, and Antonio Ricco, Stanford University/NASA ARC
The detection of life outside Earth would be an incredible discovery, revolutionizing our perception of life and providing insight into how life develops and persists in various environments. The 2011 Planetary Science Decadal Survey puts emphasis on developing capabilities to enable the search for extraterrestrial life, including sampling environments for organisms possibly living now. However, no flight-qualified instrument currently exists that has the capability to definitively test for life in these environments, nor does the astrobiological community agree on one analysis technique/instrument that would determine, without a doubt, that life exists or that there is absence of life in a planetary environment.
The most robust strategy for searching for life in extraterrestrial environments would be to employ several techniques on a mission to corroborate the detections/non-detections. Possible techniques include chirality ratios, electron-transfer/redox gradients/disequilibrium, polymer detections, physical morphology characterizations, and organic detections. Adequate sample preparation for these analyses includes removals of salts and inhibitors. We present here a sample preparation and characterization process called COOL (Characterization of Organic Life), developed for detection of long-chained molecules in planetary in situ samples. COOL has been proven on planetary analog samples [1-3] and will reach flight readiness through evaluation of a low size weight and power sequencer that can detect extracted polymers and maturation of the sample separation and extraction preparation components .
Another important application of COOL is investigating how terrestrial organisms taken into space change within those environmental conditions. Increasing our understanding of biological adaptations to micro-g, radiation, various pressures, extreme temperature swings, etc., would provide insight into life that may have evolved on extraterrestrial bodies.
 Craft et al. (2014), LPSC 45, #2929; [2 ]Neish et al. (2012), AbSciCon, Atlanta, GA;  Bradburne et al. (2012), LPSC 43, #6043;  Craft et al. (2016), LPSC 47, #3035.
ExoPAG SAG 16 Report on Remote Biosignatures for Exoplanets
Shawn Domagal-Goldman, NASA GSFC; Nancy Kiang, NASA Goddard Institute for Space Studies; Niki Parenteau, NASA ARC; and SAG 16
Future exoplanet observations will soon focus on the search for life beyond the solar system. Biosignatures to be sought are those with global, potentially detectable, impacts on a planet. Biosignatures occur in an environ-
mental context in which geological, atmospheric, and stellar processes, and interactions may work to enhance, suppress, or mimic these biosignatures. Thus biosignature science is inherently interdisciplinary. Its advance is necessary to inform the design of the next flagship missions that will obtain spectra of habitable extrasolar planets. The Exoplanet Biosignatures Workshop brought together the astrobiology, exoplanet, and mission concept communities to review, discuss, debate, and advance the science of biosignatures. This process engaged a broad range of experts by merging the interdisciplinary reaches of Nexus for Exoplanet System Science (NExSS), the NASA Astrobiology Institute (NAI), NASA’s Exoplanet Exploration Program (ExEP), and international partners, such as the European Astrobiology Network Association (EANA) and Japan’s Earth Life Science Institute (ELSI). Between these groups, we had expertise in astronomy, planetary science, Earth sciences, heliophysics, biology, instrument/ mission development, and engineering. The workshop gathered these communities in the pursuit of three goals: (1) State of the Science Review: What are known remotely observable biosignatures, the processes that produce them, and their known non-biological sources? (2) Advancing the Science of Biosignatures: How can we develop a more comprehensive conceptual framework for identifying additional biosignatures and their possible abiotic mimics? (3) Confidence Standards for Biosignature Observation and Interpretation: What paradigm informed by both scientists and technologists could establish confidence standards for biosignature detection?
Searching for Technosignatures
Jill Tarter, SETI Institute (retired) Co-authors: Martin Rees, Institute of Astronomy, Cambridge University; Michael Garrett, Jodrell Bank Centre for Astrophysics
Modifications to distant planetary environments by intelligent, technological life may be discoverable in ways not routinely investigated by astrobiologists intent on finding biosignatures. The detection of mathematicians in addition to microbes may be feasible with a search for technosignatures. Often such searches utilize the telescopic resources of the astronomers, across the electromagnetic spectrum. However, big data analytics focused on archival data from a wide range of scientific explorations, or the inclusion of detectors sensitive to artifacts among the toolkits deployed for in situ searches for biomarkers may also uncover evidence of technological civilizations. This poster summarizes historical and ongoing searches and forecasts those that may become possible with new facilities, detectors, and/or software.
On the Potential Use of Returned Samples from Mars in the Search for Life
David Beaty, JPL/Caltech, Hap McSween, University of Tennessee; Andy Czaja, University of Cincinnati; Yulia Goreva, JPL/Caltech; Libby Hausrath, University of Nevada; Lindsay Hays, JPL/Caltech; Chris Herd, University of Alberta; Munir Humayan, Florida State University; Francis McCubbin, NASA Johnson Space Center; Scott McLenna, SUNY at Stony Brook; Lisa Pratt, Indiana University; Mark Sephton, Imperial College; Andrew Steele, Carnegie; Ben Weiss, MIT; and Michael Meyer, NASA HQ
As recommended by the decadal survey Visions and Voyages for Planetary Science in the Decade 2013-2022 (2011), a crucial element of our strategy to find evidence of life of Mars is Mars sample return. The scientific planning for this is currently being led by the Returned Sample Science Board within the M-2020 Project. A summary of this planning will be presented.
Key issues/topics/questions include:
- Discovering definitive biosignatures on Mars is judged by most to be not possible with current technology, due to the heavy burden of proof by the scientific community. Therefore, studies of returned samples in laboratories on Earth are key to confirming potential biosignatures identified by rovers on Mars, and turning them into definitive biosignatures.
- There is often spatial heterogeneity of biomarker distribution and preservation about any environment, and therefore a suite of returned samples from any region of interest is key to increasing the chances of identifying definitive biosignatures.
- Martian life is likely to be microbial. Therefore the biosignatures are likely to be microscopic, and require in situ and returned sample science analyses that function on that scale. Fine-scale observations are key.
- Organic molecules are crucially important type of potential biosignature, but since contamination is a given, it is important to have well-developed strategies for contamination knowledge. The Returned Sample Science Board has considered several potential options for mitigating this problem and presented them to the Mars 2020 project.
False Negatives in Remote Life Detection: Lessons from Early Earth
Stephanie Olson, University of California, Riverside; Christopher T. Reinhard, Georgia Institute of Technology; and Timothy W. Lyons, University of California, Riverside
The Earth’s atmosphere has been an unfaithful reflection of its evolving surface chemistry and biology throughout its nearly 4-billion-year history of inhabitation. A particularly striking example from our history is the ~2.5-billion-year discrepancy between the earliest evidence for biological oxygen production and utilization on Earth and the accumulation of sufficient atmospheric oxygen to facilitate the remote recognition of an aerobic biosphere. Although the reasons for the delayed oxygenation of the atmosphere are not well understood, this delay highlights the likelihood of “false negatives” in the remote detection of life on exoplanets based on the identification of atmospheric biosignatures.
We have used an Earth system model to explore the fate of biogenic oxygen and other potential biosignature gases early in our history, and we evaluate the utility of classic biosignatures (e.g., the co-detection of oxygen and methane) for identifying and characterizing Earth’s biosphere through time. We find that extended intervals of Earth’s history may have appeared sterile based on atmospheric composition—despite major biological innovation within the ocean, including the origin of multicelluarity. At present, no single spectral feature could continuously identify life throughout Earth’s history, and no combination of existing biosignature gases could reliably characterize any stage in the evolution of life on Earth. Importantly, Earth’s cryptic biosphere arises naturally from the dynamics of ocean-atmosphere interaction in our model, and false negatives would not be unique to the early Earth; instead, false negatives may hinder remote detection of an aquatic biosphere on any Earth-like planet with an ocean at its surface. An implication is that the extrasolar bodies most likely to host life may actually be the worst candidates for remotely detecting and characterizing life.
Oxygen in Exoplanet Atmospheres: Identifying True and “False Positive” Astronomical Biosignatures
Edward Schwieterman, University of California, Riverside; Victoria Meadows, NASA Astrobiology Institute Virtual Planetary Laboratory (NAI VPL) and University of Washington; Shawn Domagal-Goldman, NAI VPL and NASA GSFC; Timothy Lyons, NAI Alternative Earths and University of California, Riverside; Giada Arney, NAI VPL and NASA GSFC; Rory Barnes, NAI VPL and University of Washington; Chester Harman, NAI VPL and Pennsylvania State University; Rodrigo Luger, NAI VPL and University of Washington; Stephanie Olson, Alternative Earths and University of California, Riverside
The spectral signatures of molecular oxygen (O2) and its photochemical byproduct ozone (O3) are the most highly referenced and studied potential biosignatures in terrestrial exoplanet atmospheres. In previous years, mechanisms for generating oxygen by abiotic planetary processes, possible “false positives” for life, were believed to be limited to planets outside of the traditional habitable zone and therefore distinguishable by simple observables such as semi-major axis. However, recent modeling work has illuminated several plausible channels for generating detectable abiotic oxygen on planets inside the habitable zone, especially for those with M-dwarf host stars. These abiotic processes would produce potentially observable independent signatures that would fingerprint the abiotic source of O2, such as CO from CO2 photolysis and O4 from the accumulation of many bars of O2 from
massive water loss. Conversely, the detection of reduced gases, such as CH4, in conjunction with O2 or O3, would establish the presence of chemical disequilibrium and a more robust signature of life. In either case, we argue that strategies for detecting life on exoplanets must include characterization of a broad enough wavelength range to capture multiple gaseous absorbing species to provide maximal context. This poster details strategies for mitigating against “false positives” by identifying the complementary signatures whose presence or absence would strengthen the case for the photosynthetic (biogenic) origin of oxygen detected in an exoplanet atmosphere. We find that the near-infrared region of the planetary spectrum contains critical contextual information with ambiguity most reduced by extending spectral analysis to 5.0 microns.
Global Surface Photosynthetic Biosignatures Prior to the Rise of Oxygen
Mary Parenteau, NASA ARC; Nancy Kiang, NASA Goddard Institute for Space Studies; Robert Blankenship, Washington University in St. Louis; Esther Sanromá, Instituto de Astrofísica de Canarias; Enric Pallé, Instituto de Astrofísica de Canarias; Tori Hoehler, NASA ARC; Beverly Pierson, University of Puget Sound; and Victoria Meadows, University of Washington
The study of potential exoplanet biosignatures—the global impact of life on a planetary environment—has been informed primarily by the modern Earth, with little yet explored beyond atmospheric O2 from oxygenic photosynthesis out of chemical equilibrium, and its accompanying planetary surface reflectance feature, the vegetation “red edge” reflectance. However, these biosignatures have only been present for less than half the Earth’s history, and recent geochemical evidence suggests that atmospheric O2 may have been at very low—likely undetectable—levels, until 0.8 Ga (Planavsky et al., 2014, Science 346:635-638). Given that our planet was inhabited for very long periods prior to the rise of oxygen, and that a similar period of anoxygenic life may occur on exoplanets, more studies are needed to characterize remotely detectable biosignatures associated with more evolutionarily ancient anoxygenic phototrophs.
We measured the surface reflectance spectra of pure cultures of anoxygenic phototrophs, and used these spectra to deconvolve complex spectra of environmental microbial mats from a variety of marine and continental environments. Rather than the “red edge,” we observed “NIR edge(s)” due to absorption of NIR light by bacteriochlorophyll (Bchl) pigments. We initially expected only to detect the pigments in the surface layer of the mats. Surprisingly, we detected cyanobacterial Chl a in the surface layer, as well as Bchl c and Bchl a in the anoxygenic underlayers. This suggests that it does not matter “who’s on top,” as we were able to observe pigments through all mat layers due to their different absorption maxima. The presence of multiple “NIR edges” could signify layered phototrophic communities in marine and continental settings, which could possibly strengthen the support for the detection of life on the surface of an exoplanet.
The Limits of Organic Life in Planetary Systems
David Smith, National Academies
The search for life beyond the Earth via in situ or remote-sensing techniques has a highly scientific, popular, programmatic, and political priority, but nothing would be more unfortunate than to expend considerable resources in the search for alien life and then not recognize it if it is encountered! To date, the search for life (e.g., by the Viking spacecraft on Mars in the 1970s) and/or planning for future searches has been governed by a model for life as we know it, so-called terran life. This approach is defensible in the absence of a general understanding of how life might appear if it had an origin independent of life on Earth. Plausible arguments can be made that if life originated independently, even within the solar system, it may not be detectable by missions carrying in situ or remote-sensing instruments designed explicitly to detect terran biosignatures. A committee established by the National Academies’ Space Studies Board in 2006 published a report, The Limits of Organic Life in Planetary Systems, which attempts to address issues relating to the detection of hypothetical non-terran life. The motivation for the study, details concerning how the committee went about its task, and the report’s principal findings and recommendations are discussed.
TARGETED PRECURSOR RESEARCH
Strategies for Life Detection in Extraterrestrial Samples
Catharine Conley, NASA HQ; Andrew Steele and Gerhard Kminek
Current international policy on performing biohazard assessments on samples brought from Mars to Earth is framed in the context of a concern for false-positive results. However, as noted during the 2012 Workshop for Life Detection in Samples from Mars (Kminek et al., 2014), a more significant concern for planetary samples brought to Earth is false-negative results because an undetected biohazard could increase risk to the Earth. This is the reason that stringent contamination control must be a high priority for all Category V Restricted Earth Return missions. A useful conceptual framework for addressing these concerns involves two complementary “null” hypotheses: testing both of them together would allow statistical and community confidence to be developed regarding one or the other conclusion. As noted above, false negatives are of primary concern for safety of Earth, so the “Earth safety null hypothesis”—which must be disproved to assure low risk to Earth from samples introduced by Category V Restricted Earth Return missions—is that “there is native life in these samples.” False positives are primarily a concern for astrobiology, so the “astrobiology null hypothesis”—which must be disproved in order to demonstrate the existence of extraterrestrial life—is that “there is no life in these samples.” The presence of Earth contamination would render both of these hypotheses more difficult to disprove. Both these hypotheses can be tested following a strict science protocol: perform analyses, interpret results, and select subsequent analyses that would increase confidence in the interpretation. The science measurements undertaken are done in an iterative fashion that responds to discoveries made, with both hypotheses testable by interpretation of the scientific data. This is a robust, community involved activity that ensures maximum science return with minimal sample use.