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Project Progress

Research by the Blake group as part of the NAI effort led by P.I. K. Nealson centers on isotopic studies of biogenic greenhouse gases as evidence for life on the large scale appropriate for remote sensing approaches and on global biogeochemical investigations. Our early work in this area with the Nealson and Yung groups was concerned with the early and present biogeochemical evolution of the Earth. We have continued this largely theoretical study, but now are also developing new tools for the exploration of Mars and other extraterrestrial environments. Our particular tracer of emphasis is stable isotope fractionation, and we seek to understand whether or not these signatures can be reliably detected in extraterrestrial solar system bodies and exo-planetary systems. We have now characterized in detail the fractionation induced by the photolysis of NNO first predicted by Prof. Yung using a combination of non-linear spectroscopic light sources and mass spectrometry or Fourier transform infrared (FTIR) spectroscopy (Rahn et al. 1998, Zhang et al. 2000, Turatti et al. 2000), and have recently developed a novel theoretical approach that can be easily extended to other systems (Blake et al. 2002).

Neither of these approaches is compatible with the stringent space and weight requirements of in situ planetary exploration strategies. We are therefore developing new technologies that should enable the in situ measurements of important radiatively and biogenically active gases such as CO, CO₂, H₂O, CH₄, NNO, and H₂S to very high precision in order to examine the atmospheric dynamics and potential biogeochemistry on Mars, Titan, and other solar system bodies. Specifically, we are using laser diodes and sensors to image infrared (IR) laser induced fluorescence (IR-LIF). The support from NAI was used to conduct pivotal modeling tests of this approach, now under development primarily with Planetary Instrument Definition and Development Program (PIDDP) support. We have recently combined microchip lasers with state-of-the-art HgCdTe detectors to investigate the sensitivity of IR-LIF under realistic planetary conditions, to optimize the optical pumping and filtering schemes for important species, and to apply the spectrometer to the non-destructive measurement of stable isotopes in a variety of test samples. These studies form the necessary precursors to the development of compact, lightweight stable isotope/trace gas sensors for future planetary missions. Thanks to support from the Astrobiology Science and Technology Instrument Development (ASTID) program to Dr. Chris Webster, this coming year we will undertake the first combined laser absorption and emission tests using miniaturized, flight-compatible diode laser spectrometers at the Jet Propulsion Laboratory (JPL). Within the NAI consortium, we will continue to work with the Nealson and Yung groups on modeling of the potential biological activity on Mars and the early Earth, and on the isotopic signatures of various model biospheres. This research is groundbreaking, and provides the necessary context for IR-LIF to be used as a robust diagnostic of extant or extinct (through its sampling of gases trapped in Martian soils and ice caps) biota on and underneath planetary surfaces.