2002 Annual Science Report
NASA Jet Propulsion Laboratory Reporting | JUL 2001 – JUN 2002
As it is presently defined, life probably arose on Earth about four billion years ago, and some of the footprints of those first organisms and of the countless others that followed have been preserved in various mineralogical records. In their efforts to learn more about the origins of life, of planets, and of biospheres, scientists are working ? with earthly and extraterrestrial samples and remote measurements ? to identify, authenticate, interpret, characterize, and classify these markers, or biosignatures, from life’s beginning.
The JPL1 NAI team began with a very broad approach to investigations of the coevolution of planets and biospheres. The strategy employed began with the use of Earth as a laboratory for the development of a suite of biosignatures that could be used across the range of environments in which life is found. At the same time, the study of ancient and modern environments on Mars was also pursued, both for comparison with those of Earth and because Mars is a prime target for astrobiological exploration. As can be seen from the work described below, this approach has continued to mature and develop over the years. In several key areas of research, the team has made significant progress over the past year.
Mineralogical biosignatures that consist primarily of iron oxyhydroxide minerals formed as the result of microbial activity in near-neutral pH solutions have been characterized. This research has established that bacteria can grow by utilizing ferrous iron (Fe2+) released by iron silicate mineral dissolution, and has identified polymer biosignatures in which pseudosingle crystals of metastable mineral phases adopt unusual dimensions as the result of polymer-directed nucleation. This work opens the door for the detection of biosignatures at the nanoscale spatial level – formation of nanocrystals as biominerals. Work is continuing with this approach in an effort to determine whether such nanocrystals can form by abiotic methods, and what the range of different types of nanocrystals is that are formed by living and metabolizing bacteria.
The fractionation induced by the photolysis of dinitrogen oxide (NNO), first predicted using a combination of nonlinear spectroscopic light sources and mass spectrometry or infrared spectroscopy, has been described in detail. A novel theoretical approach was developed that can be easily extended to other gas-phase chemical systems. A chemical model of the Martian atmosphere is being used to study the fate of several organic trace gases; the interest is in using trace gases as a test for a hypothetical subsurface biosphere on Mars. Ancient atmospheres are being modeled, and a culture system is being set up to test specific aspects of these models.
TRANSITION METALS AND ISOTOPE SIGNATURES
Work continued to explore the use of transition metal isotope fractionations as biosignatures, and to determine the extent of iron (Fe) isotope variations in natural samples from modern and ancient Earth, and to find evidence that Fe isotopes are fractionated during leaching by biogenic ligands. It appears that Fe isotopes will be sensitive indicators of past cycling of soluble pools of Fe in aqueous systems in either ancient, oxygen-poor planetary bodies that contained liquid water, or where biological cycling of Fe occurred; however, it also appears that Fe cycling in an oxygenated atmosphere, where there are not significant separable pools of Fe, will produce little Fe isotope variation. Preliminary data indicate that molybdenum (Mo) isotope fractionation also occurs during uptake of Mo into bacteria. We believe that the potential of these metal isotopes has been revealed by this work, and we also anticipate that such approaches will open new avenues for the examination of ancient samples from Earth, as well as potentially available samples from future missions.
Figure 1. Distribution of Fe isotope ratios in nature (figure courtesy of Clark Johnson).
PLANETARY PROCESSES AS ENVIRONMENTAL INDICATORS
Our team has shown that magnetization in the ALH84001 Martian meteorite dates back to 4.0 billion years, and that remnant magnetization in the meteorite provides a constraint on the evolution of Martian surface temperatures. Work on water ice vaporization and its effect on impact cratering demonstrates that much lower shock pressures are required for vaporization of ice then previously inferred. This work leads to estimates that the 2.5-km-deep Mars regolith contains 10% to 30% ice, in good agreement with recent Mars Odyssey data.
PHYSIOLOGY AND METABOLISM OF EXTREMEOPHILES
In studies of the ability of various species of bacteria to grow at extreme pressures it has been observed that cell viability is retained even after exposure to pressures of over 1,000 megapascals. Low levels of amino acid racemization repair in Siberian permafrost organisms up to 30,000 years old have been detected. This finding suggests that low-level metabolism may play a role in the retention of microbial viability over geologic time in cold environments where organisms were previously thought to be completely dormant. Work continues with endolithic (rock dwelling) extremophiles from both Antarctica and North American deserts, including the TUFA environments of Mono Lake, California. In addition, two types of extremophiles have been characterized: hyperthermophilic alkaliphiles from the thermal vents in Mono Lake, and psychrotrophic (cold tolerant) microbes from Siberian permafrost that are capable of metabolism and growth at -10 o C. The latter organsisms provide a new perspective for long-term active life, for they are capable of growth and repair under conditions that are permanently maintained in permafrost environments, and come from subsurface water lens areas of the order of 50,000 years of age.
Figure 2. Observed (solid line) and predicted (dashed line) extent of aspartic acid racemization versus 14C age in Siberian permafrost (Brinton et al 2002, Astrobiology 2, 77).
DEVELOPMENT OF IN SITU ANALYTICAL INSTRUMENTATION
Exploratory work on the development of spacecraft-based, in situ Fe isotope measurements for future Mars lander missions has begun, including novel methods for directly analyzing Fe isotopes in situ. New technologies are being developed that should enable the in situ measurement of important radiatively and biogenically active gases, such as CO, CO2, H2O, CH4, NNO, and H2S to very high precision, using laser diodes and sensors to image infrared laser-induced fluorescence (IR-LIF). Microchip lasers have been combined with state-of-the-art detectors to investigate the sensitivity of IR-LIF under realistic planetary conditions. Work is under way to describe the visible and near-infrared reflectance spectra of hyperthermophile communities and associated carbonate and silica deposits in Yellowstone National Park; to develop immunological reactions for detecting signs of life on Mars and Europa (zero-gravity tests of a prototype detection system have been performed); and to develop several novel methods for in situ detection and identification of amino acids and other organic biomarkers.
Several JPL1 co-investigators have been involved with current or proposed missions over the past year the Mars Odyssey THEMIS instrument and various submitted Mars Scout mission proposals.
EDUCATION AND PUBLIC OUTREACH
The education and outreach activities of JPL1 have focused for the most part on informal education, particularly interactions with museums and related institutions. Team members have collaborated with the Los Angeles County Museum of Natural History on the Skymobile mobile interactive exhibit, culminating this past year with the rollout of the exhibit itself. This exhibit and its accompanying curriculum-enhancement program are now rotating among elementary schools in the Los Angeles Unified School District. In collaboration with NAI Central and other NAI teams, a national survey of museum astrobiology content and interests has been initiated..
In the final year of its initial 5-year term, the JPL1 team will work to consolidate the knowledge gained in the research described above, and to position itself to apply that knowledge to the ongoing exploration of Mars and other Solar System bodies. Several instrument development projects in which team members are participating have the potential to result in instruments that can be proposed for the 2009 Mars Smart Lander mission, for future Mars Scout missions, and also perhaps for future outer Solar System missions under the New Frontiers program. The team will also seek to take advantage of opportunities to help shape the growing interface between geobiology and astrobiology, through individual and collective interactions with the new Program in Geobiology at the University of Southern California. This combination of terrestrial research, extraterrestrial exploration, and educational activities will underlie the continued success and accomplishments of the team.