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Executive Summary

The University of Colorado Center for Astrobiology brings together researchers who focus on scientific issues related to the origin and history of life here on Earth, the potential for life to exist elsewhere in our solar system, and the distribution of planets around other stars and their potential habitability. The participants in our effort span the range of scientific disciplines that comprise astrobiology and, by coming together in an academic and intellectual environment, provide a breadth of expertise that provides cross-cutting scientific leadership. Our efforts include research in the various sub-disciplines of astrobiology, teaching of undergraduate students, graduate students, and post-doctoral researchers both in the individual sub-disciplines and across all of astrobiology, and outreach to the broader university and public communities. Together, they add up to a vibrant program in astrobiology that reaches out across a substantial fraction of the university intellectual landscape. Here, we describe the components of our astrobiology program emphasizing, in order, the research, teaching, and outreach activities.

Research program in astrobiology. Our research efforts can be divided up into several themes:

1. The origin and evolution of life on Earth. Topics here include issues related to the origin of life and the genetic, the evolution of biochemical functions, the earliest recorded history of the Earth and of life on it, microbial diversity and life in extreme environments, and major evolutionary events in life’s history.

   
   

   Under Prof. Michael Yarus’ leadership, we are continuing our investigation into the smallest number of RNA molecules that can yield active RNA structures, now using experimental rather than theoretical approaches. Other related work has yielded interesting results, now being prepared for publication. These related experiments determine the number of consecutive randomized nucleotides required to isolate the simplest isoleucine binding RNA by selection. This work shows that unexpectedly short RNAs are best, the binding activity being most easily isolated with 26 consecutive random nucleotides. This is much shorter than expected, and in particular, the fact that adding nucleotides (to make longer starting sequences) is not helpful (but instead somewhat inhibitory) is particularly hard to explain. What seems to be implied is that there is an unanticipated potent difficulty inhibiting the search for RNA active sites in longer starting sequences.

   
   

   In an effort that involves collaboration between biochemistry (from Prof. Shelley Copley) and philosophy (from Prof. Carol Cleland), we have been exploring the potential for the existence of a “shadow biosphere” that consists of microbes that are not descended from life as we know it and that does not use the same biochemical structures and strategies to support metabolism, growth, and reproduction. Such a biosphere might exist in parallel to the standard life, but be undetectable by techniques that detect the standard biochemical molecules. Today, 99.9 % of microbes in the environment cannot be cultured, suggesting that there are a tremendous number of organisms about which we know essentially nothing.

   
   

   Studying the ancient Earth and its biosphere is difficult because of the paucity of samples. Prof. Stephen Mojzsis and his group have been searching out samples and analyzing them. Their work on mass-independent fractionation of sulfur isotopes in ancient sediments provided data that: (i) places limits on the geochemical record of the transformation of the surface zone to an oxygen-rich environment between 2.5 and 2.3 billion years ago, possibly at the expense of methane; and (ii) described a means to investigate traces of early microbial metabolisms that utilized sulfur as an oxidant and provided data proposing the appearance of this metabolic style early in the Archean. In addition, research on Th/U coupled with the geochronology of zircons has traced the metamorphic transition from amphibolite to the granulite facies that dominates the geological history of all rocks that are more than 3.7 billion years old. This allows us to describe the metamorphic history of the oldest terranes and better glean clues concerning the habitability of the early Earth.

   
   

   In the area of microbial diversity, projects continue to revolve around development and use of rRNA-based molecular methods to study the microbial constituents of ecosystems in extreme environments without the requirement for cultivation of the organisms. Some properties of organisms can be inferred from the phylogenetic results, and the sequences can be used to design hybridization probes to visualize organisms and their interactions in the environment. Recent results include: (i) Studies of Guerrero Negro hypersaline microbial mats showed that Green Non-sulfur bacteria, not cyanobacteria, dominate hypersaline microbial mats; this has impact on expected mechanisms of carbon fixation, isotope fractionation, and other geochemical parameters. (ii) The ongoing Guerrero Negro studies have discovered and identified by sequence more than 7000 novel microbes, some only distantly related to known organisms; the number of bacterial kingdoms was expanded from about 60 to about 80 in this study! (iii) The newly discovered acidic Yellowstone endolithic community is an entirely novel biome with relevance to the possibility of life on Mars and to the search for past life there.
   
   Based on DNA sequence identity, Prof. William Friedman and his group have identified the symbiotic fungi associated with early land plants throughout their life cycle. These symbiotic fungi represent an ancient lineage of fungi that are known to form essential symbiotic fungal associations with most extant plants. The co-evolution of this ancient symbiotic fungal association throughout land plants potentially facilitated the evolution of the current complexity of terrestrial life. We have compared the fungal symbionts in the subterranean life cycle phases of early land plants to the fungal symbionts present in neighboring photosynthetic plants. These data suggest that the underground life cycle phases in these early plant lineages obtain carbon through a fungal network. Recent research suggests organisms that survive catastrophic impacts typically have an underground component such as a spore, or seed. Thus, a long-lived subterranean life cycle phase in early land plant lineages may have increased ability to avoid extinction following an asteroid impact by obtaining carbon through a fungal network.

   
   

2. The origin and evolution of habitable planets. Topics within our program relate to the habitability of planets, both in our solar system and beyond.

   
   

   At Mars, Prof. Bruce Jakosky and collaborators are exploring the geochemical energy that can support metabolism via chemical weathering at low temperatures on Mars. Such low-temperature environments may be widespread, based on recent discoveries and analyses pertaining to Martian gullies, sub-freezing liquid water, crater lakes, and depositional environments. Our results will be used to determine which types of geological environments are most suitable for supporting Martian organisms, and what the availability of energy as a resource is. To answer these questions, we have been using three different geochemical reaction modeling programs (EQ3/6, PHREEQC, and Geochemist’s Workbench); these simulate the mixing of water with various host rock compositions based on Martian meteorites, to determine geochemical weathering pathways, and to estimate available energy that can support metabolism. This approach will allow us to determine the conditions that have optimal geochemical energy available to organisms.

   
   

   An issue being explored by Prof. Robert Pappalardo that is crucial to understanding the potential habitability of Europa is whether the satellite’s level of internal activity has remained relatively constant, has waned through time, or is cyclical with periods of greater and lesser activity, each of which represents a physically plausible scenario. If Europa’s level of internal activity is high today, its potential to harbor life is significantly greater than if the satellite’s internal heat sources have dwindled over time (or if they cyclically diminish to negligible levels). To explore this, we have implemented a quantitative method of temporally ordering Europa’s geological features based on their cross-cutting relationships as mapped within Geographic Information Systems software. It allows us to group lineaments that have indistinguishable positions in the stratigraphic order. These lineaments can be treated as roughly contemporaneous, and used to investigate the changes in orientation and origin of the surface stresses through time. As a test case, this method has been applied to the lineaments of the Conamara Chaos region. We find that there are some intersecting lineaments that were either truly contemporaneous, or were re-activated after their initial formation.

   
   

   Prof. Brian Toon and his group are exploring the factors controlling climate on terrestrial planets and their implications for planetary habitability. Some of the specific results from the year include: (i) Experimental studies show, as had been predicted in some theoretical studies, that the production rate of aerosols declines as the abundance of CO₂ relative to methane increases in simulated ancient terrestrial atmospheres. (ii) Additional experimental studies show that polycyclic aromatic hydrocarbons and terpene related compounds can form in Titan’s atmosphere, with the unexpected result that the type of organic compounds formed shifts for CH₄ to N₂ ratios close to those in Titan’s current atmosphere. (iii) A study of the escape of H₂ from the atmospheres of extrasolar planets and from the early Earth explains the observed structure of one extrasolar planetary atmosphere, and shows that planets can evaporate in the inner solar system. The terrestrial work points to hydrogen rich atmospheres with hydrogen partial pressures above 1 bar on early Earth.

   
   

   Although Dr. Tom McCollom’s funding as an NAI team member does not begin until this year, initial research on his project has already begun. The goal of the research is to develop numerical models of chemosynthetic-based ecosystems on Earth that will provide insights into possible analog environments on the early Earth, Mars and Europa. Towards this end, numerical models of serpentinization of ultramafic rocks and their potential to support chemolithoautotrophic microbes has been initiated. While it is too early in this research to draw specific conclusions, the initial results suggest that H₂-based microbial communities living on ultramafic rocks in the subsurface should be much more productive by several orders of magnitude than those based on basaltic or granitic rocks.

   
   

   Prof. John Bally is investigating how planets are born. In what type of environment, and under what conditions do most stars (and associated planetary systems) form? How do grains and gas in proto-planetary systems evolve from interstellar properties to solid bodies? His group has been using the world’s largest telescopes (such as the Keck 10m and Gemini 8m telescopes) to search for answers at wavelengths between 0.5 and 20 microns. They have found evidence for proto-planetary disks in the Carina nebula, which is a much harsher environment for star and planet formation than the comparable Orion nebula. They also used the Gemini-South 8m telescope to obtain thermal infrared images, sensitive to the presence of 100 to 500 Kelvin dust, of young stars embedded in the Orion nebula. These data show that most of Orion’s “naked” young stars (in Hubble Space Telescope images) nonetheless are surrounded by warm dust. His group also has found that ultraviolet (UV) radiation can actually enhance the onset of gravitational instabilities in disks, leading to “triggered” planetesimal formation. They are developing a numerical model to study the combined effects of UV-induced photo-ablation and other processes, to understand the onset of self-gravitational condensation into planetesimals.

3. Societal and philosophical issues in astrobiology. The major task in this theme is being carried out by Prof. Carol Cleland from the Philosophy Dept. at CU, and is described above.

4. Astrobiotechnology development. We are providing national leadership in development of technology for use in astrobiology flight missions. The major tasks to date have involved formation of an Astrobiotechnology Focus Group (reported on separately) and its sponsorship of the upcoming workshop on Mars Astrobiology Science and Technology. That workshop will address needs for Mars flight missions beyond the 2009 Mars Science Laboratory, and will instigate development of concepts and instruments.

Teaching program in astrobiology. Each of the CU Co-Investigators involves undergraduate students, graduate students, and/or post-doctoral researchers in their laboratories and groups. In addition, we offer: (i) An undergraduate course in “Extraterrestrial Life” that has been offered every semester for seven years, has typically 75 students enrolled each semester, is taught by one of the Co-Investigators (and has been taught by Jakosky, Bally, Pappalardo, and Mojzsis, for example), and uses the textbook co-authored by PI Jakosky (“Life in the Universe”, by Bennett, Shostak, and Jakosky). (ii) An undergraduate course in “Alien Cultures: Astrobiology, Science, and Society” discusses the societal and philosophical issues in astrobiology with senior undergraduate science majors. (iii) A graduate course in “Astrobiology”, aimed at students in both the physical and biological sciences, provides a broad training across the discipline. (iv) A graduate course in “Philosophy of Astrobiology” brings together students from both the sciences and astrobiology. (v) A graduate certificate in Astrobiology demonstrates training across the disciplines.

Outreach program in astrobiology. A central part of our program involves outreach beyond the astrobiology researchers on campus. Our program this year is substantially expanded from in previous years, and activities this year included: (i) A public symposium on Mars, tied to the Mars Exploration Rover missions; (ii) A traveling public symposium to take the excitement of astrobiology to schools catering to under-represented minorities, with visits this year to Ft. Lewis College and Hampton University; (iii) Open houses to get the public excited about the Mars missions, attracting a total of approximately 700 to the two Mars landings; and (iv) A science journalism workshop, aimed at providing in-depth training on the astrobiological relevance and significance of the Mars rover missions, run pre-landing and attended by about sixteen main-stream journalists.