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Executive Summary

Overview

The year 2009 saw the revival of the Astrobiology Program at Arizona State University, building on the legacy of the CAN1 ASU NAI Team headed by co-I Jack Farmer (1999-2004). As summarized below, significant effort began on 18 of the 19 research tasks described in our CAN5 proposal. This effort resulted in ~ 50 publications that appeared in print, were submitted or reached an advanced state of preparation during the reporting period. Collectively, this initial research sets the stage for our goal of integrating life science, geoscience, planetary science and astrophysics to understand how the distribution of chemical elements shapes the distribution of life in space and time, and to guide the search for life beyond Earth.

In addition to this research, a vibrant suite of EPO activities was undertaken. These activities reached a variety of constituencies, including K-12 children and educators, college students, and the public at large. They provide a foundation for several major EPO initiatives we are planning.

As important as it is that we met the tangible goals of spinning up our research and EPO efforts, we were also successful in these first few months in developing the astrobiology research community through intra-team activities at ASU, such as weekly informal meetings and co-sponsorship of astrobiology-oriented seminars. These efforts resurrected an enthusiastic and cohesive astrobiology community at ASU that includes faculty, staff, graduate and undergraduate students. These include not only the co-Is, collaborators and students who constitute the formal membership of the ASU Team, but also a larger cross-section of ASU scientists and students who are excited to learn about, and contribute to, our astrobiology research and EPO efforts. This overall community is impressively multidisciplinary, consisting of individuals with expertise that runs, literally from A to Z – from astrophysics to zoology.

We fostered connections with other teams, notably through research collaborations with scientists at the Montana State University, MIT and NASA Ames Teams detailed in this report. We catalyzed new research collaborations by inviting members of the JPL Icy Worlds team to join our inaugural “all hands” meeting, by hosting a visit of the PI of the JPL Titan team in June, 2009, and by helping to host the Strategic Workshop held in May, 2009, in Tempe, AZ.

We developed human resources in astrobiology by providing stipend support to 6 postdocs (4 female; 1 African-American) and 12 graduate students (6 female) during the reporting period.

Our team received strong support from ASU administration in these efforts. Notably, we were given sole access to ~ 1500 sq. ft. of newly renovated laboratory, office and meeting space. This space is ideally located, adjacent to the main building of the School of Earth & Space Exploration, which is the center-of-gravity for the ASU Team. In addition, the university provided the project $100,000 of support from a special strategic fund, above-and-beyond commitments in the CAN5 proposal.

Below we summarize the research progress-to-date in each of our three major project components. We also briefly review our EPO activities, emphasizing key highlights of Year 1.

Research Progress

The organizing principle of the “Follow the Elements” project is the need to understand the identity and use of bioessential elements by prokaryotic organisms and the distributions and abundances of these elements in potentially habitable, water-rich extraterrestrial environments. To this end, the project is organized around three major research themes: The Stoichiometry of Life; The Habitability of Water-Rich Environments; and Astrophysical Controls on the Elements of Life. We pursue each theme by way of a number of focused research tasks. The status of each task is comprehensively described in the main report. In this Executive Summary, we summarize the progress-to-date.

1. The Stoichiometry of Life

This theme includes several tasks aimed at elucidating relationships between the availability of bioessential elements and prokaryotic ecosystems. These tasks involved: quantitative laboratory growth experiments, centered on model prokaryotes grown in nutrient-limited chemostats (Task 1); field studies and associated laboratory analyses at Yellowstone National Park and Cuatro Cienegas, Mexico (Tasks 2a and 2b, respectively); evolutionary studies in the geologic and genomic records (Tasks 3a and 3b, respectively); and a modeling project to understand the interconnections between the biogeochemical cycles of carbon, oxygen and bioessential nutrient elements in prokaryote-dominated oceans (Task 4).

In the initial 7 months, technician Marcia Kyle, working under the guidance of co-I Jim Elser, designed and established the chemostats for Task 1 (Figure 1). These are located in ~ 1000 sq ft. of recently renovated research labs made available by ASU for our astrobiology team. Procedures were tested and refined using the photoautotroph Synechocystis sp. PCC 6803, which is the organism to be used in our first round of nutrient-limited growth experiments. These experiments will follow the physiological and molecular responses to N, P and Fe limitation, testing the ability of this organism to cope with limitations of three bioessential elements. Subsequent rounds of experiments will work with extremeophiles. Establishing these chemostats was therefore a key early milestone for our project, and so the stage was set for the first round of experiments to begin early in Year 2. Several other lab-based projects were also advanced during this time, including collaborator Felisa Wolfe-Simon’s exploration for As-based life, co-I Susanne Neuer’s investigation of exopolymer production in response to nutrient stress, and graduate student Jennifer Glass’ investigations of Mo storage by N2-fixing cyanobacteria.

Also during this time, we undertook two expeditions to initiate the field portion of our project. The major field project for Year 1 took place in July and August, when approximately 30 faculty, staff and students spent two weeks obtaining samples and conducting experiments at Yellowstone National Park under the leadership of co-I Everett Shock (Task 2a). This expedition provided samples well suited to our goal of tracing the use of bioessential elements in the extreme ecosystems found in this park, and the influences that element availability may have on microbial distributions. A smaller, scouting expedition to Cuatro Cienegas, Mexico took place in February (Task 2b), led by co-I Elser and collaborator Valeria Sousza. This expedition set the stage for intensive fieldwork by graduate student Jessica Garvin. These activities support our plan to experimentally manipulate the phosphorus budget of one of the Cuatro Cienegas Pozas in Years 3 and 4.

Investigations into the evolutionary record of element use and cycling (Tasks 3a and b) were highlighted by a series of papers published or nearing publication in Year 1, particularly those emerging from the Astrobiology Drilling Project in Western Australia, led by ASU Team PI Ariel Anbar and co-I Tim Lyons earlier in the decade. These included two publications in Science, which provided strong evidence that small amounts of O₂ present in the oceans before the Great Oxidation Event affected the cycling of nitrogen and iron (Figure 2). Year 1 also saw a sampling trip to China by co-I Lyons and planning for a similar trip to Australia by Lyons and postdoc Amy Kelly, to collect Proterozoic drill core samples for our planned investigation into coupled variability in redox, element budgets and microbial ecology revealed by inorganic and organic geochemistry – the latter to be spearheaded by collaborator Gordon Love in coordination with the MIT NAI Team. Genomic efforts in Year 1 centered on various investigations of the evolution of the nitrogen cycle by co-I Jason Raymond, co-I Janet Siefert and PI Anbar in collaboration with the MSU NAI Team. Siefert and collaborator Chris DuPont secured additional support for an expanded menu of activities in Year 2 and beyond, including, respectively, DOE support for a transcriptomic investigation of Cuatro Cienegas and NAI DDF support to reconstruct the relative ages of all known metal-binding protein families.

The modeling investigations at the heart of Task 4 were initiated by co-I Watson Gregg. The initial findings confirm expectations that nutrient cycling would be different in prokaryote-dominated oceans as compared to modern oceans, but also reveal that such ecosystems pose computational challenges for existing ocean biogeochemical models.

2. The Habitability of Water-Rich Environments

This goal of this theme is to improve our ability to infer the availability of bioessential elements in aqueous environments on Mars, in the outer Solar System, and on water-rich exoplanets. It includes tasks involving: Improving computational codes to model water-rock interactions (Task 1); application of modern geodynamics codes to ice dynamics on Europa and other icy bodies (Task 2); integration of these and other computational models with observational data to better assess the habitability Europa (Task 3), Mars (Task 4), other small icy bodies (Task 5), and postulated extrasolar “waterworlds” (Task 6). Significant progress began on all tasks, except for Task 6, which is deferred for future years.

Co-I Mikhail Zolotov and collaborator Mikhail Mironenko began to address the deficiencies of existing thermodynamic computational codes, emphasizing challenges of properly incorporating the activity of water in highly saline fluids (Task 1).

In Task 2, collaborator Allen McNamara, a geophysicist who uses numerical methods to study the dynamics of planetary interiors, turned his talents to convection in the ice shell of Europa. Such convection is a critical path by which materials from the interior ocean can reach the surface, and so inferences about the subsurface from existing and future surface data require quantitative understanding convective processes. Working with graduate student Melissa Bunte, McNamara is focusing initially on the dynamics of the ice-water interface at the base of the ice shell. Results will be presented at AGU in Year 2.

Co-I Zolotov and collaborator Ron Greeley set the stage for future efforts to assess the habitability of the Europa ocean (Task 3) by finalizing a review chapter on the chemistry of the postulated ocean (Zolotov) and by advancing plans for the next NASA flagship mission to the outer planets, the Europa-Jupiter System Mission (Greeley).

Task 4 was advanced by co-I Farmer and a number of ASU graduate students who collected and analyzed samples from siliceous hot springs in Yellowstone National Park to calibrate the ability of various analytical techniques that will be flown on MSL or future missions to extract mineralogical and compositional information from continental hydrothermal environments. Additionally, co-I Zolotov and coworkers published the results of thermochemical models designed to explain the formation of observed mineralogical assemblages observed in the Martian meteorite ALH84001 and on the surface of Mars.

Several highly innovative and interdisciplinary results emerged under the umbrella of Task 5. Focusing on Kuiper Belt Objects (KBOs), co-I Steven Desch and students carried out a careful assessment of the internal evolution of Pluto’s moon Charon using numerical methods, published in Icarus (Figure 3). They found that preservation of liquids is possible even to the present day in the presence of just a few percent ammonia mixed with water in these icy bodies. If so, there may be as much “ocean” volume in the Kuiper Belt as on the Earth. This finding also raises the possibility that cryovolcanism modifies the surfaces of these objects, potentially explaining some spectral observations and providing a window into internal composition from data returned by future missions. Graduate student Simon Porter and Desch have explored some of these issues in another paper submitted to Icarus. Separately, Desch worked with co-I Everett Shock and graduate student Christopher Glein to apply theoretical geochemical considerations to understand the origin of Titan’s atmosphere. They conclude that methane in this atmosphere is likely primordial, while molecular nitrogen was probably produced by hydrothermal reactions of primordial ammonia. A manuscript on this work is in press. Glein also contributed to a study published in Nature demonstrating that the internal composition of Saturn’s moon Enceladus, as revealed by analyses of its plumes, may consist of primordial cometary materials and hydrothermally produced N2. Zolotov also studied Enceladus’ plumes, concluding that their composition is strongly primordial, as will be detailed in a presentation at the AGU meeting in Year 2.

3. Astrophysical Controls on the Elements of Life

This theme aims to elucidate the influence of supernovae and other nucleosynthetic processes on the formation of solar systems, their composition and evolution. A particular focus is the production and distribution of the short-lived isotope ²⁶Al, the abundance of which may affect the distribution of water in rocky planetesimals and planets. The theme includes tasks involving: High-precision isotopic studies of meteorites to quantify the timescales of the injection of supernova-derived materials (Task 1); computational modeling of the physical and chemical evolution of massive stars (Task 2); quantification of the injection of supernova ejecta to star-forming molecular clouds (Task 3) and protoplanetary disks (Task 4); modeling the chemical evolution of star-forming regions (Task 5); determining what elements might be used as observational proxies in stellar spectra for elements and isotopes not amenable to direct observation (Task 6); and incorporate element abundance data in the “HabCat” of nearby stars that could support life (Task 7).

Initial research in Task 1 focused on high-precision Pb-Pb age dating of the earliest Solar System solids, the calcium-aluminum-rich inclusions (CAIs) found in carbonaceous chondrites. Of particular note, graduate student Greg Brennecka, working with co-I Meenakshi Wadhwa and PI Anbar, found significant variations in the ²³⁸U/²³⁵U ratio in 13 CAIs (Figure 4). This ratio has been presumed to be uniform – an assumption which underlies Pb-Pb geochronology. The observed variations therefore lead to a significant revision of early Solar System chronology. Because the variations likely result from decay of short-lived ²⁴⁷Cm in the early Solar System, they also provide new constraints on the timescale of solar nebula formation. At the close of Year 1, this work was in revision for publication in Science.

An array of projects was pursued as part of Task 2 by co-Is Frank Timmes, Patrick Young and several graduate students to improve our understanding of stellar evolution. These projects included new 3D simulations of core collapse supernova explosions, combined with improved treatment of nuclear reactions and hence element and isotope production. A key area of investigation in these studies is the effect of asymmetries and other 3D effects on the production of elements – especially ²⁶Al. With graduate student Mike Pagano, Young is also pursuing observational studies of the variation in element abundances of nearby stars and in coeval populations of stars. These studies generated several published and submitted papers to the Astrophysical Journal.

Task 3 and Task 4 are closely linked, under the leadership of co-Is Desch and Timmes, working with collaborators Young and Evan Scannapieco. Task 3 represents a new research effort, involving two newly hired postdocs, using advanced computational codes to simulate the dynamics of molecular clouds and their interaction with supernova ejecta. Task 4, building on prior work by Desch and colleagues, resulted in three papers submitted to the Astrophysical Journal during Year 1. The most novel, led by graduate student Carola Ellinger, blended meteoritics and astrophysics to assess how much of a shift in solar nebula oxygen isotope compositions would accompany a supernova injection sufficient to account for the ²⁶Al injection inferred from meteorite studies.

Task 5 centers on the process of “self enrichment” of stellar clusters, whereby they evolve chemically as isolated systems. Accurate modeling of self enrichment requires careful treatment of the propagation of ionization fronts. Year 1 was devoted to developing a tractable approach to this difficult problem, which is now being prepared for publication.

The major goal of Task 6 is to determine what elemental proxies in stellar spectra could be used to trace the production and distribution of ²⁶Al. This is a highly integrative exercise, drawing on and feeding into several of the preceding tasks. Hence, the core collapse simulations completed in Task 2 were used by Ellinger and Young to discover that the sulfur to silicon ratio and the abundance of phosphorus may be good tracers. Computational modeling undertaken as part of Task 6 also supported Ellinger’s work under Task 4 (above). Task 6 will also be informed by the observational studies Young began planning to undertake with Pagano, summarized above under Task 2.

The ultimate goal of Tasks 1 – 6 is to help focus the search for life outside our Solar System. Hence, it is necessary to compile a database of element abundances in nearby stars against which model predictions and expectations can be compared. To this end, in Task 7, co-I Timmes worked with collaborator Margaret Turnbull and graduate student Nahks Tr’Ehnl to incorporate spectroscopically derived elemental abundance data intoa subset of Turnbull’s “HabCat” database (Figure 5). In parallel, graduate student Pagano worked with collaborator Young, co-I Timmes and collaborator Jade Bond to develop chemical evolution models that can explain compositional variations among stars that were recently discovered by Bond. Both efforts are being developed into publications.

EPO Progress

We initiated a rich slate of EPO activities in our initial months that included formal and informal educational initiatives as well as outreach activities of national scope. Highlights are given below.

In formal education, ASU Team members were heavily involved in developing a new Astrobiology curricular track in the B.S. program in the School of Earth & Space Exploration. The degree “B.S. in Earth & Space Exploration with Astrobiology Concentration” will be offered beginning in 2010, in parallel with concentrations in Geological Sciences and Astronomy/Astrophysics. We expect that this exciting but academically demanding program will attract strong students to the field. In another formal curricular effort, PI Anbar began to develop the curriculum for a new course, Habitable Worlds, to be offered to freshman non-STEM students beginning in Fall, 2010. This course will also be part of the curriculum of a new B.A. program in Earth & Space Studies that will be offered in the School of Earth & Space Exploration.

In informal education, our initial emphasis was to leverage existing EPO efforts at ASU, particularly in the Mars Exploration Program. This collaboration enabled us to reach ~ 100 K-12 educators by joining a pair of previously planned workshops. Of note, we were able to integrate a unique astronomically oriented astrobiology curricular module developed by collaborator Patrick Young. We expect to continue such efforts. Additionally, during summer, 2009, co-I Wendy Taylor joined the Yellowstone National Park field expedition in order to begin to collect imagery and video for a “virtual reality field trip” that we intend to produce in future years.

In outreach, ASU Team members engaged in a wide range of activities, across a range of scales. Of special note was the involvement of many ASU Team members in the Origins Symposium at ASU in early April, 2009, organized by collaborator Lawrence Krauss, who heads the Origins Initiative at ASU. This event involved ~ 70 exceptional scholars from around the world, including several Nobel Laureates, engaged in symposia for the general public as well as technical sessions. ASU Team members were active in these sessions and as part of the organizing committee. An outreach highlight was a broadcast of NPR’s Science Friday from the ASU campus. Half of this program, devoted to astrobiology, consisted of a panel discussion with ASU Team PI Anbar and collaborator Paul Davies, together with former NAI Director Baruch Blumberg and noted astrobiologist Peter Ward.