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Executive Summary

The central goal of the Goddard Center for Astrobiology is to understand how organic compounds are created, destroyed, and altered during stellar evolution leading up to the origin of life on a planet, such as Earth. Planetary systems form by collapse of dense interstellar cloud cores. Some stages in this evolution can be directly observed when stellar nurseries are imaged, while other stages remain cloaked behind an impenetrable veil of dust and gas. Yet to understand the origin of life on Earth, we must first develop a comprehensive understanding of the formation of our own planetary system. To understand the probability of finding life elsewhere we must understand both the similarities and differences between the evolution of our own system and that of a typical star.

Dense cloud cores are very cold (10-50 K); their dust grains are coated with ices comprised of water and organic compounds. Many of these organics have potential relevance to the origin or early evolution of life, if delivered to planets. The survival of these organics through the violent birth-phase of a star is less certain. Properties of the young star (its mass, spectral energy distribution, whether it formed in isolation or as a multiple star, etc.) help control the evolution of organic material in the proto-planetary disk. The location within the disk is important since the nature and effectiveness of such processing depends strongly on distance from the young star, on distance above the nebular mid-plane, and on time. The ultimate delivery of these primitive organics to young planets and their moons also evolves with time, as the bodies grow in size and as the nebula clears.

We seek to better understand the organic compounds generated and destroyed in the interstellar and proto-planetary environments, through observational, theoretical, and laboratory work. We have begun to examine the potential for and limitations to delivery of exogenous pre-biotic organics to planets, examining factors that enhance or restrict this potential. To follow these factors over time, from the natal cloud core through the end of the late heavy bombardment (~ 4.1 Ga) and evaluate the possible role of exogenous organic material in terrestrial biogenesis, we have divided the research into four themes as well as our education and public outreach program. These themes are:

Theme 1: Establish the taxonomy of icy planetesimals and asteroids to evaluate their potential for delivering pre-biotic organics and water to the young Earth and other planets.

Theme 2: Investigate processes affecting the origin and evolution of organics in planetary systems

Theme 3: Conduct laboratory simulations of processes that likely affected the chemistry of material in natal interstellar cloud cores and in proto-planetary disks.

Theme 4: Develop advanced methods for the in-situ analysis of complex organics in small bodies in the Solar System.

This second year of our NAI participation saw major emphasis on infrastructure: recruiting students, staff, and permanent employees, updating computational facilities, building laboratories, and furnishing them with equipment. In addition to the 5 undergraduate students recruited through our summer internship program we recruited 2 additional undergraduates and 2 high school students for part-time work. Beyond this we recruited a graduate student, 3 post-doctoral researchers, a senior soft money scientists (Oliver Botta), and hired one civil servant (Daniel Glavin).

Our Team members conducted a vigorous and highly productive research program, and participated in numerous meetings and workshops. We conducted many laboratory and field investigations (mainly astronomical), as outlined below and in the individual reports of Progress.

At Goddard, we sponsored a vigorous Seminar Series in Planetary Sciences and Astrobiology (see Agenda).

In addition to planting these seeds for the future, our Team members made significant progress in meeting our scientific goals:

Progress in Theme 1:

A primary objective of Theme 1 is to establish a taxonomy of icy planetesimals based on their chemical compositions. Such measurements are important for establishing the role of comets in replenishing Earth’s oceans after Earth-Moon formation, and for delivering the seed organic molecules from which life emerged.

In our second year, Mumma, DiSanti, and their collaborators quantified CO, C₂H₆, and other volatile organic constituents (along with H2O) at high spectral resolution in three comets: the short-period Jupiter Family Comet (JFC) (73P/Tempel 1) and two long-period, Oort cloud comets (C/2001 Q4 and C/2004 Q2). Infrared spectra of 73P/Tempel 1 were obtained at high spatial and spectral resolution before and after Deep Impact — abundances were measured for H2O and six other parent volatile species. Relative to water, ethane was severely depleted in material released before impact, but its abundance in the impact ejecta was higher by a factor of three and was consistent with the value found for “typical” Oort cloud comets. Although these comets are now stored in very distinct reservoirs, it appears that they may have originated in a common region of the proto-planetary disk (see Report by M. Mumma).

Graduate student Boncho Bonev (Univ. of Toledo, in residence at Goddard) is nearing completion of his Ph. D. dissertation on OH prompt emission in comets as a direct tracer of H₂O production, and he delivered a FAR Seminar on this topic.

Along with HCN and NH₃ (both of which we also study at IR wavelengths), exogenous delivery of H₂CO is thought to play a particularly significant role in seeding Earth with pre-biotic chemicals. Analysis of infrared spectra of Oort cloud comet C/2002 T7 (acquired in year one) provided a clear detection of H₂CO. Retrospective analysis by DiSanti has now revealed formaldehyde in six other comets. Comparison with CO and CH₃OH has provided a first look into the oxidation state of volatile carbon in these comets, showing that it varies greatly among them, possibly a signature of radial gradients in the protoplanetary disk (see report by M. DiSanti).

Co-I Blake and collaborators acquired millimeter-wave observations of HCN in comets C/NEAT (2001 Q4) & C/LINEAR (2002 T7), based on OVRO and BIMA Array spectra and images (Friedel et al. 2005). Their next step is to compare the physical model developed to explain the HCN emission with those developed by GSFC co-Is (Mumma, DiSanti, et al.) to explain a suite of infrared observations of these comets. These results form an interesting counterpoint to the compelling Deep Impact spectra gathered at Keck by the Astrobiology team and recently published in Science (Mumma et al. 2005). (see Report by Blake).

Co-I Charnley and collaborators performed a series of radio observations of comets C/2001 Q4 (NEAT) and C/2002 T7 (LINEAR) using the JCMT and the ARO 12m and SMT telescopes. They detected deuterated formaldehyde (HDCO) in C/2002 T7, its first detection in a comet. The inferred D/H ratio is large, consistent with formation in a very cold environment, and a paper is being prepared for submission to Nature. (see Report by Charnley).

Co-I Charnley and collaborators made preliminary studies of gas-grain deuterium fractionation processes in the comet-forming regions of model proto-planetary disks. Their disk chemistry model includes multiple deuteration driven by H₂D^{/SUP>, HD₂} and D₃⁺ reactions. They also published several Reviews describing models of disk chemistry and the connection between these processes and the composition of primitive solar system materials. (see Report by Charnley)

Co-I Fegley and collaborators (Washington Univ.) investigated chemical and isotopic composition of presolar grains found in chondritic meteorites, and atmospheric chemistry during the accretion of Earth-like planets. Collaborators Lodders and Sachiko Amari published an invited review regarding the origin and nebular processing of carbonaceous presolar grains. They describe the search for presolar grains, the different types of presolar grains, the chemical and isotopic composition of the different types of grains, and their origin from different stellar sources. (see Report by Fegley)

Co-I Richardson and post-doc Graeme Lufkin (Univ. Maryland) modified their gravitational simulation code to handle a prescribed migration of a giant planet through a disk of planetesimals. Initial results suggest that giant planet migration is not a catastrophic event for disks of planetesimals. The eccentricity and inclination of the planetesimals are greatly increased by the giant planet, but less than twenty percent actually get ejected from the system. Further growth of the planetesimals will be postponed until dynamical friction and gas drag can cool their orbital motion. Richardson and Zoë Leinhardt (Harvard) quantified the effect of fragmentation (based on a rubble pile model) during the early and middle stages of planetary growth. For the parameters tested, fragmentation did not play a dominant role compared to simulations that assumed perfect accretion. In addition, debris created in these simulations did not significantly affect the dynamics of the larger bodies. (see Report by Richardson)

Co-I Fegley and Laura Schaefer modeled the chemistry of silicate vapor and steam-rich atmospheres formed during accretion of Earth and Earth-like exoplanets (planetary accretion models show temperatures of several thousand degrees during Earth accretion). They predict spectroscopically observable gases that can be used to search for Earth-like planets forming in other planetary systems. Silicon monoxide (SiO) gas is the major species in silicate vapor atmospheres for T > 3080 K, and monatomic Na gas is the major species for T < 3080 K. During later, cooler stages of accretion (1500 K), the major gases (abundances >1%) in a steam-rich atmosphere are H₂O, H₂, CO₂, CO, H₂S, and N₂. Carbon monoxide converts to CH4 as the steam atmosphere cools. They also calculated the composition of volatiles outgassed from chondritic planetary bodies, finding that the major out-gassed volatiles for certain starting compositions are CH₄, N₂, NH₃, H₂, and H₂O. This important result predicts that Earth’s earliest permanent atmosphere was a reducing atmosphere that favored synthesis of organic compounds by Miller — Urey type reactions initiated by lightning, UV light, and heat. (see Report by Fegley)

Co-I Walker is fingerprinting late additions to the Moon using the relative abundances of the highly-siderophile elements (HSE) that occur in generally high abundance in likely impactors, but extremely low abundance in the indigenous lunar crust. Towards this end, approximately 2g of several Apollo 14 and 17 melt breccias were obtained from the Johnson Space Center curatorial facilities. Walker is pursuing this goal in collaboration with Dr. Odette James (USGS retired) – a longstanding expert on these rocks. In the second year, they cleanly separated chips from 73215, 73255 and 72395, and analyzed them for Os isotopes and highly siderophile element abundances (Pt, Pd, Ir, Ru, Re and Os). The Apollo 17 rocks likely sample the Serenitatis basin impactor. All rocks analyzed have 187Os/188Os ratios of approximately 0.129 to 0.133. These ratios are consistent with the Serenitatis impactor having long term Re/Os similar to enstatite or ordinary chondrites, rather than carbonaceous chondrites.

Progress in Theme 2:

A vital component of Theme 2 is the observation of star- (and planet-) forming molecular clouds and of the later proto-planetary disks. This work highlights the role of prebiotic chemistry long before planetary surfaces are amenable to the synthesis of such compounds, and suggests that the chemistry leading to life is widespread throughout the universe. Since the physical conditions vary among and within such clouds, it is important to investigate the chemical and physical processes in a variety of such environments.

Irvine and colleagues in Korea have been studying molecular clouds in the vicinity of the center of our Milky Way Galaxy, where various energetic processes can influence the chemical composition of molecular clouds. They observed millimeter-wave transitions of the molecules CO, HCO⁺, HNCO, and SiO toward the Sgr A region using the SEST telescope at LaSilla, Chile. The comparison of the observed transitions shows that the several prominent gas condensations in this region have very distinctive chemical properties with respect to each other, which may result from differing physical conditions in the various locations (Minh et al., 2005). (see Report by Irvine)

Pedelty, in collaboration with Mundy, planned and implemented Very Large Array (VLA) observations of the hot molecular cores (HMC) in the young stellar object IRAS 16293-2422. These 7 mm observations targeted the prebiotic molecules formic acid, methyl formate, and ethyl cyanide in sources A and B within this object – several species were detected (see Report by Pedelty).

Charnley and collaborators published Submillimeter Array maps of organic molecules in the 'hot corinos’ of the low-mass IRAS 16293-2422 binary system (Huang et al. 2005). Their new H13CN interferometric data clearly shows Keplerian rotation in sub-source A, and hence the presence of a protostellar accretion disk. A VLA proposal was submitted with NAI — GCA collaborators L. Mundy and J. Pedelty to perform high-resolution observations of this source at cm wavelengths. (see Reports by Pedelty and Charnley).

Mundy also continues his work on Spitzer projects of relevance to the early evolution of planet-forming disks. Of particular interest are the studies of cold outer disk systems that are being found through their emission in the IRAC 8 micron and MIPS 24 micron bands. The nature and evolutionary state of these systems is unclear at this point; they could be post-classical T Tauri systems that have not yet lost their outer disks; they could be more evolved systems with outer debris disks created by planetesimal collisions. Continued work with the large dataset associated with the Cores to Disks Spitzer Legacy project is likely to provide answers. (see Report by Mundy)

Using Spitzer, Blake and collaborators detected the signatures of organic molecules in ices located in the outer regions of the potentially protoplanetary disk CRBR 2242, and the abundances so obtained can be directly compared to those in comets (Pontoppidan et al. 2005). More excitingly, perhaps, they detected the gas phase absorption bands of the organics HCN, acetylene, and CO₂ that likely arise from the inner disk encircling IRS46 (another ~edge on disk in Ophiuchus, Lahuis et al. 2005). If substantiated by further observations, this source would provide the first opportunity to examine the hot (several hundred Kelvin) organic chemistry predicted to occur in the planetesimal formation region sampled by carbonaceous chondrites in our own solar system. (see Report by Blake)

Young stars are often intense sources of X-ray emission, and energetic processing of material in the proto-planetary disk could be efficient if X-rays are present in the very earliest phases before accumulation and clearing are complete. To produce pre-biotic materials in the cold circumstellar environment of the young Sun, high-energy radiation may be required to stimulate chemical reactions of molecules. Strong X-rays from the stellar core can be a significant source of such radiation, and therefore the history of their X-ray activity can be quite important. With the XMM-Newton X-ray observatory, Hamaguchi, Petre, and collaborators clearly detected for the first time strong X-ray emission from one of the earliest stages of a star at the age of 10,000-100,000 years, the so-called Class-0 protostellar phase. This demonstrates the presence of X-ray luminosity before disk clearing and suggests the importance of chemical processing in this way. (see Report by Petre).

Another aspect of Theme 2 is the search for and characterization of exoplanets. D. Deming and collaborators achieved the first detection of infrared light from an exoplanet. They applied the Spitzer Space Telescope to observe HD 209458 in and out of secondary eclipse (the star occults the planet). They quantified the difference of infrared light and showed that the amount coming from the planet agreed with models for its size and temperature. A second group achieved independent detection of a second transiting exoplanet using another instrument on Spitzer. Its significance lies in demonstrating that exoplanets can be characterized by astronomical methods. The Deming paper appeared in Nature in 2005, and the second group published their result in the Astrophysical Journal also in 2005. These Spitzer detections are the first direct measurements of planets orbiting other stars, and they open a new era in astronomy and astrobiology, where we can now directly study and compare alien worlds to those in our own solar system. Deming and Mumma and their collaborators are developing other spectral methods for characterizing the atmospheres of exoplanets. (see Report by Deming)

Progress in Theme 3:

Theme 3 is entirely focused on laboratory work. One aspect simulates the vacuum and low-temperature environment of space using a high vacuum chamber and a cryostat. Ice samples condensed on a cooled mirror inside the cryostat are irradiated with 1 MeV protons to simulate cosmic-ray bombardment or are photolyzed to simulate vacuum-UV exposure.

Co-I Dworkin finalized construction of the laboratory infrastructure in our Organics Analysis Laboratory. Significant electrical upgrades were installed along with state-of-the-art analytical equipment for determining the organic composition of the material generated in the Cosmic Ice and Cosmic Dust Laboratories, amino acid contamination in Stardust aerogels, and measurement of meteoritic organics. Dworkin and collaborators optimized conditions for the analysis of amino acids and nucleobases and are working to increase sensitivity and decrease contamination. This lab is now in full operation and is producing original research. Initial investigations include identifying refractory organic compounds in radiation processed ices, in organics produced on reactive smokes by Fischer-Tropsch like catalysis, and in chondritic meteorites. Dworkin is actively collaborating with other laboratories from Themes 3 and 4 of the GCA and from the CIW and Ames NAI teams. (see Report by Dworkin)

Co-Is Moore and Hudson simulate the low-pressure and temperature environment of space using a high-vacuum chamber and a cryostat in the Cosmic Ice Laboratory. Ice samples condensed onto a cooled mirror inside the cryostat are irradiated with 1-MeV protons, to simulate cosmic-ray bombardment, or are photolyzed to simulate vacuum-UV exposure. Motivated by detections of glycolaldehyde (HOCH₂CHO) and ethylene glycol (HOCH₂CH₂OH) in the interstellar medium and, for ethylene glycol, in comet Hale-Bopp, they examined the low-temperature formation of these molecules. They found that irradiated methanol-containing ices produced ethylene glycol, and that ices containing this molecule produce glycolaldehyde, a simple sugar. In addition they determined that energetic processing of aliphatic alcohols produces aliphatic aldehydes and vice versa. Other new results are the detection of several amino acids in residues that resulted from irradiations of nitrile ices. (see Report by Moore and Hudson)

Co-I Nuth and Natasha Johnson (NAS-NRC) investigated production of both volatile and macromolecular carbonaceous materials via surface mediated reactions on silicate dust grains in the laboratory, to evaluate such processes in the nebular environment. They found that almost any free surface catalyzed the Fischer-Tropsch-Type conversion of CO and molecular hydrogen to complex hydrocarbons. These reactions produced a macromolecular carbon coating on the grain surface that itself acted as a catalyst for formation of hydrocarbons containing nitrogen when the reaction occurred in the presence of N₂, H₂ and CO. Far from acting as a poison, these coatings can greatly enhance the reactivity of some grain species such as amorphous magnesium silicate or silica particles. They continue to study initial composition of the volatile organic species produced on both amorphous iron-silicate and magnesium-silicate grains as a function of time, temperature and degree of previous reaction products deposited on the grains’ surfaces. (see Report by Nuth)

Co-I Nuth and Yuki Kimura demonstrated that CaO and Ca(OH)₂ are excellent candidates to explain the 6.8 μm feature, one of the most enigmatic spectral features in young stellar objects. Earlier attempts to identify the precursor emphasize organic materials. Nuth and Kimura hypothesize that this feature is produced in the hot interiors of young stellar environments via distillation of Ca from pre-existing hibonite dust followed by the condensation of CaO and Ca(OH)₂ grains. (see Report by Nuth)

Progress in Theme 4:

The development of instruments for organic analysis on space missions is the crux of Theme 4. To prepare for flyby, rendezvous, and sample return missions to comets the development of advanced organic analysis techniques has been initiated. These techniques include: laser desorption mass spectrometry; pyrolysis mass spectrometry; and the solvent extraction of organic molecules followed by chemical derivatization. In the initial stages of this work a variety of Mars analog materials such as Atacama desert soils, Hawaiian basalts, meteoritic samples, and solid material generated by some of the nitrile irradiations conducted by Theme 3 have been used to cross compare these techniques. Some of these materials also serve as cometary analogs and the chemistries developed for their analysis may be relevant for future cometary research.

Co-I Mahaffy and collaborators are developing protocols for analysis of complex organic materials on space missions. During the second year, Dr. Arnaud Buch returned to a university position in Paris and plans were made for his replacement with another highly qualified astrobiologist, Dr. Oliver Botta. Botta arrived in August. His work will combine studies of organics in suitable analogues for comets and Mars with analysis of meteoritic and other terrestrial samples using GC-MS. Dr. Botta has several different types of meteorites that will be analyzed for their amino acid composition. In addition, he will study the organic composition of Antarctic meteorites with respect to contamination from the ice. In related work, Daniel Glavin has initiated a program to investigate the distribution and isotopic composition of nucleobases in carbonaceous meteorites that was also supported (in 2004) by the Exobiology program. This research is a collaborative effort between NASA Goddard (Jason Dworkin and Oliver Botta), Carnegie Institution of Washingon (Marilyn Fogel) and the Leiden Institute of Chemistry in The Netherlands (Zita Martins). Martins spent the summer in residence at Goddard pursuing this research. (see Reports by Mahaffy and Dworkin)

Co-I Brinckerhoff (JHU/APL) work at JHU/APL is developing laser desorption (LD) and time-of-flight mass spectrometry (TOF-MS) techniques that complement ongoing non-laser GCA work at GSFC; they sample distinct yet related sets of compounds from complex samples. Advances made during year two included a “flight-scale” breadboard leveraged and completed with completed with separate NASA instrument support. (see Report by Brinckerhoff). Initial analyses of carbonaceous chondrites and simple carbon-matrix standards with laser desorption methods have contributed to a developing database of refractory macromolecular materials that may be present in comets and other small bodies. This database should lead to increased understanding of (i) parent body synthesis and processing; (ii) impact survival of more fragile incorporated compounds; and (iii) enhanced in situ protocols for determining the full breadth of cometary organics.

Education and Public Outreach:

Finally, our team has made great progress in our education and public outreach endeavors. In 2005 we hosted the second group of students under our Summer Undergraduate Internship in Astrobiology (SUIA) program. Students are paired with mentors based on their expressed research interests, and they spend 90% of their time actually doing research. Summaries of their research appear in the Reports by Deming, DiSanti, Dworkin, Mahaffy, Moore, and Mumma, and again in our EPO report. Three team members (Irvine, Hudson. Moore) developed and taught undergraduate Astrobiology courses at their institutions (Univ. Mass – Amherst, Eckerd College, and University of Maryland College Park). EPO lead S. Stockman (with other team members) also conducted year two of a high school curriculum development project with the Minority Institution Astrobiology Collaborative (MIAC). We are also jointly developing a capability to systematically observe comets through emission-line filters at optical wavelengths. This effort is led by MIAC member Dr. Donald Walter (South Carolina State University), working with (with GCA co-I DiSanti), and will utilize telescopes in Arizona. Imaging studies on the Kitt Peak 1.3-m telescope are in the science-testing phase.

Planetary Science and Astrobiology Seminars

October 1, 2004 — September 30, 2005

October 7	Anthony Remijan, NRC, NASA/GSFC, Earth and Space Data Computing Division “Recent Observations in Interstellar Chemistry: New Constraints for Detecting Large Biomolecules and the Discovery of Two New Molecules Toward Sgr B2(N-LMH)”
October 21	Jocelyne DiRuggiero, University of Maryland, Department of Cell Biology and Molecular Genetics “Life on the Edge: Functional Genomics of Extremophilic Microorganisms”
November 4	Daniel Glavin, NASA/GSFC Atmospheric Experiment Branch “A Search for Extraterrestrial Amino Acids in Antarctic Meteorites: Implications for the Analysis of STARDUST Grains”
November 18	Alan Boss, Carnegie Institution of Washington Department of Terrestrial Magnetism “Giant Planet Formation and Implications for Astrobiology”
December 2	Doug Hamilton, University of Maryland, Department of Astronomy “Tilting Saturn”
January 6	Sean Solomon, Department of Terrestrial Magnetism, Carnegie Institution of Washington. “The MESSENGER Mission to Mercury: Seeking Clues to the Formation and Evolution of the Inner Planets”
January 18 & 20	Planetary Science and Astrobiology Posters Highlights from 2004 Building 28 Atrium, 2:00-4:00
February 3	Ah-Son Wong, NRC/USRA, University of Michigan Planetary Science Laboratory. “Atmospheric Chemistry of Mars: Methane and Oxidants”
February 10	Jason Dworkin, LEP, Astrochemistry Branch “Life Before RNA”
March 3	Bill Farrell, LEP, Planetary Magnetospheres Branch. “Mars Dust Storms, Electric Fields, and Associated Chemistry”
March 17	Yanping Guo, Johns Hopkins University Applied Physics Laboratory “The New Horizons Mission to Pluto and the Kuiper Belt”
April 7	Carol Grady, GSFC/UV/Optical Astronomy Laboratory “The Evolution of Planetary Systems: An Observational View of the First 10-20 Myr of the Nearest Young Stars and Their Disks”
April 14	Amitabha Ghosh, Univ. of Tennessee, Department of Earth and Planetary Sciences “Case for and Against Al26 and Electromagnetic Induction Heating”
May 5	John Cooper, GSFC/Earth-Sun Exploration Division “Habitability in High Radiation Environments: The Case for Life at Europa”
May 19	Derek Richardson, University of Maryland, Astronomy Department “Asteroids and Satellites: Origins and Implications”
June 2	Gözen Ertem, GSFC/Astrochemistry Branch “Formation of Phosphodiester Bond in Aqueous Solution by Montmorillnite Catalysis to Produce RNA-Like Oligomers: A Model Study”
August 15	Tom Halasinski, St Joseph’s University, Department of Chemistry “Investigations of Nitrogen Containing Aromatic Molecules in ISM via Matrix Isolation Spectroscopy: Where is the Nitrogen in Space?”
September 29	Mike Mumma, NASA/GSFC Solar System Exploration Division “Deep Impact: A Comet’s Volatile Secrets Exposed”

NAI Distributed Workshop: Methane on Mars:

The GCA hosted the East-coast site for a distributed Workshop on Mars methane on May 18. The Workshop was sponsored by the NAI and organized by Bruce Runnegar, Mike Mumma, and Mark Allen. “Gordon Conference” Rules were adopted to encourage free and open interchange. About 50 people participated from four geographic sites (CAB, Spain; NASA Ames; CAB, Australia; Goddard). M. J. Mumma opened the Workshop with a balanced view of work by the three groups reporting detections of methane on Mars. Craig Manning (UCLA), Barbara Sherwood-Lollar (Toronto), Chris House (Penn State), and Mike Summers (George Mason Univ.) provided excellent overviews of terrestrial analogues, and Dorothy Oehler, T. C. Onstott, and Barbara Sherwood-Lollar contributed additional 10-minute remarks. Abstracts in the attached agenda provide a good synopsis of the formal talks.

Methane on Mars: NAI Distributed Workshop

May 18, 2005

8:00-14:30 PDT NASA Ames Research Center, California, USA

11:00-17:30 EDT NASA Goddard Space Flight Center, Maryland, USA

16:00-23:30 CEST Centro de Astrobiologia del CSIC-INTA, Madrid Spain

Introductory remarks

Bruce Runnegar, NASA Astrobiology Institute, Ames Research Center, Moffett Field, CA 94035, USA; Bruce.Runnegar@nasa.gov

Spectral observations of methane on Mars

Michael J. Mumma, Goddard Center for Astrobiology, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA; Michael.J.Mumma@nasa.gov

Abstract: Three groups have reported independent detections of methane on Mars. I will review the current status of these searches. On Mars, the photochemical lifetime of methane is very short (~300 years), and any methane now in its atmosphere must have been released within that time. However, the lifetime could be very much shorter if heterogeneous processes destroy methane efficiently, and this would require that estimated production rates be revised upwards. I will present evidence supporting the presence of strong latitudinal (meridional) gradients, obtained by our team. These gradients require: 1. significant local sources of methane, and 2. a removal mechanism that is much more rapid than photochemistry. The destruction lifetime might be shorter than the meridional circulation time (of order weeks), i.e., several thousand times faster than photochemistry and this provides an important quantitative constraint for assessing the release rate. The combination provides an important constraint for assessing biogenic vs. primordial or geothermal origins.

Terrestrial analogs 1 — water-rock reactions

Craig E. Manning, Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567, USA; manning@ess.ucla.edu

(No Abstract available)

Terrestrial analogs 2 — deep crustal methane

Resolving abiogenic versus biogenic sources of methane and implications for Mars exploration.

Barbara Sherwood-Lollar, Department of Geology, University of Toronto, Ontario, Canada M5S 3B1; bslollar@chem.utoronto, ca

Sherwood Lollar, B.¹, Telling, J.¹, Lacrampe-Couloume, G.¹, Slater, G.F.², Onstott, T.C.³ and Pratt, L.M.⁴. (1Department of Geology, 22 Russell St., University of Toronto, Toronto, Ontario Canada M5S 3B1 bslollar@chem.utoronto.ca. ²School of Geography and Geology, McMaster University, Hamilton, Ontario L8S 4K1. ³Dept. of Geosciences, Guyot Hall, Princeton University, Princeton NJ 08544. ⁴Dept. of Geological Sciences, Indiana University, Bloomington IN 47405)

Abstract: To date the characteristics of abiogenic hydrocarbons have not been well defined. Studies of terrestrial abiogenic gases have shown that measuring the delta 13C value of methane alone is not always diagnostic. If the source of carbon is mantle-derived, as at the mid-ocean spreading centers, the delta 13C value of the methane would be expected to be relatively enriched in 13C. Away from mantle carbon input however, in crustal-dominated systems such as deep Precambrian Shield rocks, processes of water-rock interaction (including serpentinization) produce abiogenic hydrocarbons that may have much more isotopically light (12C-rich) signatures, reflecting local crustal carbon sources. Drawing on field data from terrestrial abiogenic gases and recent laboratory experiments, this paper will address key parameters that may be used as diagnostic tools for identifying biogenic hydrocarbons versus abiogenic geological sources of methane and other hydrocarbons, in particular the pattern of 13C and 2H variation between methane and higher hydrocarbon gases such as ethane.

Terrestrial analogs 3 – biogenic methane

Christopher H. House, Department of Geosciences, Pennsylvania State University, University Park, PA 16802, USA; chouse@geosc.psu.edu

Abstract: Methanogens, members of the Euryarchaeota, inhabit diverse of anaerobic habitats on Earth ranging from polar sediments to hydrothermal vents. The phylogenetic, environmental, and metabolic diversity of methanogens and methanotrophs will be discussed. Also, an overview of carbon isotopic fractionation during methanogenesis will be presented.

Fate of Disequilibrium Trace Gases in the Martian Atmosphere

Michael E. Summers, School of Computational Sciences, Department of Physics and Astronomy, George Mason University, Fairfax, Va 22030

Abstract: The recent discovery of methane in the atmosphere of Mars has provided a new approach for indirectly probing possible disequilibrium chemistry beneath the Martian surface. Methane in the Martian atmosphere has a chemical lifetime of less than about 300 Earth years, thus its existence in the atmosphere may suggest a continuous replenishment. Its chemical lifetime is several orders of magnitude longer than typical atmospheric transport timescales, and thus its mixing ratio is to first order expected be fairly uniform throughout the Martian lower atmosphere, except possibly near localized source regions. A measurement of its average value would thus provide an estimate of the total magnitude of its source. In order to use measurements of methane as a probe of its source strength, it is important to understand its fate in the atmosphere. The chemical destruction of methane in the terrestrial atmosphere has been extensively studied. Analogous processes are likely to dominate the destruction of gaseous methane on Mars. Specifically, ultra-violet photolysis and chemical reactions between methane and both OH (hydroxyl) and O(1D) are probable loss processes on Mars. The oxidation of Martian methane will have an inconsequential impact on the overall chemical structure of the atmosphere, but understanding the details of the oxidation process may provide a means to use measurements of small variations of atmospheric methane to locate source regions. Also, understanding the kinetics of methane chemical destruction on Mars also provides a theoretical framework for understand the chemical loss of other possible disequilibrium gases such as H2S, NH3, HCN, and CH2O, that might exist in the Martian atmosphere. These latter species probably have chemical lifetimes substantially shorter than that of methane, and their distributions in the Martian atmosphere will probably show strong correlations with their respective source regions. And finally, understanding the isotopic fractionation of methane in the Martian atmosphere may provide a means to use isotopic measurements as constraints on the nature of the methane source.

Working session/brief contributions:

Dorothy Oehler

T.C. Onstott

Barbara Sherwood-Lollar