Research Objectives and Activities

The past or present occurrence of life on an extraterrestrial planet does not ensure our ability to detect it. Recognition of life or its processes requires biosignatures that are clearly discernible against a landscape of abiotic processes, which may vary widely depending on the host environment. The overarching goal of this investigation is to provide astrobiological search strategies and missions with an enhanced understanding of factors that control biosignature formation. Our approach recognizes that astrobiology search targets fall predominantly into two categories: those where detailed observation and/or physical sampling is (or could be) feasible, and those where assessment of biogenicity must be made exclusively via telescopic observation.

The first category (detailed observation and sampling) includes only bodies in our solar system. Presently, Earth is the only planet on which liquid water is stable against the atmosphere, and may therefore be the only one capable of supporting a surface biosphere. The possibility of an extant biosphere on other solar system bodies is thus limited to the subsurface, where water is stable but light is unavailable as an energy source. Metabolism in such environments must limited to non-photosynthetic anaerobic processes than can be supported by the local geochemistry. Thus, a portion of our effort is devoted to exploring the biological and biosignature potential of possible subsurface environments on other planets in our solar system, via studies of analogous environments on Earth.

The subsurface environments we will study are basaltic and ultramafic (olivine-rich) rocks that contain liquid water. These rock types are (and were) abundant on planetary bodies: the crusts of differentiated bodies (Earth, Mars, Venus, 4 Vesta) contain basaltic and ultramafic rock, and most undifferentiated bodies (chondritic asteroids) are composed entirely of ultramafic rock. Liquid water reacts spontaneously with rocks of this type to generate H2 (which could fuel microbial metabolism) and the aqueous alteration mineral serpentine (which could preserve biosignatures in a resilient lithified form). Our studies will focus on a series of northern California springs that percolate through ophiolite host rocks (sections of basaltic/ultramafic ocean crust that have been obducted onto land). These springs offer perhaps the best available terrestrial analog for the early and modern Martian crust (noting that recent orbital and landed Mars research has demonstrated abundant ultramafic mineralogy at the Martian surface). Our preliminary studies show that these springs support a microbial community, and likely possess an aqueous chemistry capable of providing energy to non-photosynthetic microbes. The principal objectives of our ongoing studies will be to:

(i) Determine whether the microbial life in ophiolite-hosted alkaline springs leaves a residual mineral biosignature. We emphasize the mineralized component of this process because, in the astrobiological exploration of Mars, everything older than a few tens of millions of years (~99% of Mars history) will either be a rock or will only be interpretable in the context of the rocks that contain it. The inclusion of the CheMin definitive mineralogy instrument on the planned Mars Science Laboratory (with Investigation 4 science team member David Blake as principle investigator) makes these terrestrial ophiolite mineralogy studies particularly relevant and timely in the context of Mars exploration.

(ii) Assess the energetic requirements of these biological systems in order to establish boundary conditions on their potential distribution in a planetary subsurface. For example, the Spirit rover has uncovered evidence of aqueous alteration of ultramafic rocks on Mars. This process would liberate energy, a fundamental requirement of life. But could they have provided enough energy, at a fast enough rate, to support a viable biology as a guide to sampling strategies on future life-detection missions.

For bodies beyond our solar system, any assessment of inhabitance must be made telescopically, via a basic analysis of atmospheric chemistry. It is generally believed that photosynthetic biospheres offer the best possibility for telescopic detection because: (a) by harnessing starlight as an energy source, a photosynthetic biosphere can attain a level of productivity orders of magnitude greater than that possible in a non-photosynthetic one; (b) photosynthetic biospheres can drive planetary surface chemistry dramatically away from thermodynamic equilibrium (whereas non-photosynthetic life catalyzes planetary chemistry towards equilibrium), and this disequilibrium condition may itself represent a potential biosignature. While photosynthetic biology is the engine that drives the production of chemical biosignatures, the composition and magnitude of biosignature flux ultimately depend on the specific nature of interactions between photosynthetic and non-photosynthetic elements of the biosphere. These interactions govern, for example, whether photosynthetic productivity is partitioned into volatile versus non-volatile forms, or into compounds that are diagnostically biogenic versus those that are merely ambiguous. As such, they directly impact the detectability of putative extrasolar biospheres. Thus, the second major element of this investigation focuses on examining the nature of interactions between photosynthetic and non-photosynthetic microorganisms in tightly and loosely coupled associations, in order to understand the mechanisms by which photosynthetic productivity is transformed into detectable biosignatures.

The principal objectives of this task are to:

(i) Determine the ultimate fate of photosynthetic carbon and electrons within several model oxygenic and anoxygenic photosynthetic microbial ecosystems, with particular emphasis on potentially diagnostic and detectable biosignatures;

(ii) Determine the chain of organisms, and organism-organism interactions that are involved in transforming photosynthetic productivity into biosignatures;

(iii) Understand how the community-level mechanisms of biosignature production are influenced by changes in the physico-chemical environment, with particular emphasis on parameters that may vary substantially during planet-biosphere co-evolution.

The major thrust of this second task is to support telescopic search for life missions, such as terrestrial planet finder and life finder. Notably, however, this work will also carry particular relevance for Mars exploration, because the terrestrial ecosystems under study occur in hypersaline evaporite basins - similar to the apparently widespread environment that has been encountered by the Opportunity rover at Meridiani Planum.

Astrobiology Roadmap Goals and the NASA Vision for Exploration

This investigation is closely aligned with both Astrobiology Roadmap goals and the NASA vision for exploration. The focus on biosignatures, and on the evolution of planetary chemistry through biological processes, squarely addresses roadmap goals 4 and 7. (See Astrobiology Roadmap at http://astrobiology.arc.nasa.gov/roadmap/). Similarly, the focus of task one on bioenergetics will help to direct the search for past or present habitable environments within the solar system (from an energy perspective), in direct support of roadmap goal 2.

This work also directly supports astrobiology-oriented exploration missions that are highlighted within the exploration vision. Mineralogical studies of aqueous alteration in ultramafic rocks, and studies of biosignature formation in saline evaporite settings, are directly relevant to current and future geological, chemical, and biological assessment of the environments now being characterized on the surface of Mars. Additionally, studies of the formation of volatile biomarkers in phototrophic systems will provide a critical biological perspective for the design and interpretation of telescopic search for life missions (e.g. , terrestrial planet finder). Our work will be strongly integrated into the Mars science program in particular, with the direct involvement of team members Des Marais (as long-term planning lead for Spirit in the current Mars Exploration Rover Mission) and Blake (as the PI for the CheMin instrument package, in conjunction with Treiman and Des Marais, for the forthcoming Mars Science Laboratory) in Mars mission planning and execution.

Education and Public Outreach

Investigation 4 team members participate materially in an array of high-impact outreach activities. These activities include:

- Yellowstone National Park signs and exhibits program (Des Marais and Hoehler)
- California Academy of Sciences astrobiology exhibit program (Des Marais and Hoehler)
- Jason Project (Jahnke)
- Lunar and Planetary Institute intensive teacher workshops (Treiman, workshop leader and Hoehler)
- Aliens of the Deep Educator's Guide (Hoehler)

Go to the Education and Public Outreach section for more details on the activities listed above.

Recent Highlights

	Dave Des Marais has represented Ames and the investigation 4 science team as the long-term planning lead for the Spirit rover that is currently exploring Mars as part of the MER mission.
	David Blake's instrument CheMin, has been selected as part of the science payload for the forthcoming Mars Science Laboratory. CheMin permits X-ray fluorescence and diffraction measurements on small samples of ground rock, providing definitive mineralogy information. Dave leads an instrument team that also includes investigation 4 team members Allan Treiman and Dave Des Marais.
	Tori Hoehler participated in the filming of "Aliens of the Deep", a James Cameron-directed Disney IMAX film about hydrothermal vent life and its possible implications for life on Europa. Tori appeared nationally on "CBS Sunday Morning" to discuss the film's astrobiology content. He also helped to design and review an educators guide, with a heavy focus on astrobiology that has been distributed to teachers nationwide.

Ames Team Members Participating in this Investigation

NAME	ROLE	ORGANIZATION	EMAIL
Hoehler, Tori	Lead Co-Investigator	NASA Ames Research Center	Tori.M.Hoehler@nasa.gov
Albert, Daniel	Co-Investigator	University of North Carolina, Chapel Hill	dan_albert@unc.edu
Blake, David	Co-Investigator	NASA Ames Research Center	dblake@mail.arc.nasa.gov
Bradley, Alex	Doctoral Student	Massachusetts Institute of Technology	bradleya@mit.edu
Canfield, Don	Collaborator	Odense University (Denmark)	dec@biology.sdu.dk
Castenholz, Richard	Co-Investigator	University of Oregon	rcasten@darkwing.uoregon.edu
Des Marais, David	Principal Investigator	NASA Ames Research Center	David.J.DesMarais@nasa.gov
Fleming, Erich	Collaborator	University of Oregon	efleming@darkwing.uoregon.edu
Green, Stefan	Post-Doc	NASA Ames Research Center	sjgreen@mail.arc.nasa.gov
Jahnke, Linda	Co-Investigator	NASA Ames Research Center	Linda.L.Jahnke@nasa.gov
Orphan, Victoria	Co-Investigator	California Institute of Technology	vorphan@gps.caltech.edu
Pace, Norman	Collaborator	University of Colorado	nrpace@colorado.edu
Schulte, Mitchell	Co-Investigator	NASA Ames Research Center	Mitchell.D.Schulte@nasa.gov
Spear, John	Collaborator	University of Colorado	spearj@colorado.edu
Summons, Roger	Collaborator	Massachusetts Institute of Technology	rsummons@mit.edu
Thamdrup, Bo	Collaborator	Odense University (Denmark)	bot@biology.sdu.dk
Treiman, Allan	Co-Investigator	Lunar And Planetary Institute	treiman@lpi.usra.edu
Turk, Kendra	Doctoral Student	California Institute of Technology	kat@caltech.edu
Visscher, Pieter	Co-Investigator	University of Connecticut	pieter.visscher@uconn.edu
Vogel, Marilyn	Post-Doc	NASA Ames Research Center	mvogel@mail.arc.nasa.gov

See the following Ames Team research pages:

Formation and Evolution of Habitable Planets
Prebiotic Organics from Space
Origin and Early Evolution of Proteins and Metabolism
Biosignatures in Chemosynthetic and Photosynthetic Systems
Modeling Ecosystems and Biospheres
Hind-Casting Past Environments
Interplanetary Pioneers