Shallow-Borehole Array for Measuring Greenland Emission of Trace Gases as an Analogue for Methane on Mars (GETGAMM). This project is a 3-year, multimillion dollar grant funded by NASA Astrobiology Science and Technology for Exploring Planets (ASTEP).
Planetary exploration of Mars is rapidly advancing with high-resolution data from orbiting and landed instruments upending the image of a monotonously arid red planet and raising interest in the search for evidence of extant Martian life. The plausibility of biotic influences on release and sequestration of water and other volatile molecules on Mars remains a highly contentious topic. Despite this uncertainty, treating volatile emissions as potential atmospheric biomarkers is prudent for planetary protection and is critical for refinement of exploration strategies aimed at life detection on Mars. Using deeply eroded Paleoproterozoic bedrock in southwestern Greenland as an analogue for Mars, a team of scientists from Indiana University, Princeton University, Goddard Space Flight Center, the Jet Propulsion Laboratory, and Honeybee Robotics is participating in a three-year field campaign to analyze seasonal and diurnal variation in concentration and isotopic composition of methane, ethane, and hydrogen sulfide in bedrock boreholes (0.5 to 2 m depth) and soil pipe wells (0.5 to 1 m depth) intersecting permafrost environments in a study site aligned with a highly fractured, regional shear zone.
Open-path laser spectroscopy (OPLS) is the basis for detection of methane from a variety of bedrock and vegetated terrains in periglacial settings. A hand-carried laser source and retro-mirror reflector are deployed at transects perpendicular to the strike of the shear zone. OPLS data combined with soil-gas samples are used to target specific sites for seasonal and diurnal monitoring of trace-gas release to the atmosphere.
An innovative gas-exchanging drill string coupled to a percussive drill has been developed as part of the GETGAMM project in order to monitor subsurface gas emissions along the shear zone. A commercial, soil-gas pipe well is used to collect samples from the top of the permafrost in peatlands and along lake margins. Gas-tight syringes attached to capillary lines allow rapid transfer of unaltered gas samples from the drilled boreholes and the soil-gas pipes into analytical instruments. The field campaigns will culminate in the third year with an integrated drill-packer-optic-capillary system as a technology demonstration of semi-autonomous drilling for planetary exploration.
During three years of sequential field campaigns in southwestern Greenland, we propose to measure seasonal and diurnal variation in concentration and isotopic composition of methane in bedrock boreholes (0.5 to 2 meters in depth) and soil pipe wells (1 to 1.5 meters in depth) intersecting permafrost environments across a study site of about 1 square km. Three instruments will be deployed for the measurement of methane isotopic compositions in the field: a multi-path tunable laser spectrometer that is optimized for carbon isotope discrimination will be contributed by the Jet Propulsion Laboratory; a cavity ring down spectrometer capable of both carbon and hydrogen isotopic measurements will be contributed by a collaboration between Goddard Space Flight Research Center and Princeton University; and a commercially produced integrated cavity output spectrometer from Los Gatos designed for carbon isotopic measurements will be operated by Indiana University. Isotopic compositions determined in the field will be validated using duplicate flask samples and injection into conventional gas-source isotope ratio monitoring mass spectrometers in the Stable Isotope Research Facility at Indiana University.
Drilling in the first two field campaigns will be progressively more robotic, leading to a technology demonstration in the third year of semi-autonomous drilling to depths of 2 meters with an integrated compression packer to seal the borehole and install one fiber optic and two capillary tubes. At time intervals of days to months, gas in the sealed boreholes will be transferred without atmospheric contamination to a suite of above ground instruments using the capillary tubes.
The GETGAMM campaign directly addresses the challenge of determining concentrations and isotopic compositions for methane in soil-gas or fracture-gas samples as a means to ground truth reports of methane plumes in the Martian atmosphere. A coordinated field test of three methane instruments will allow on-site comparison of analytical sensitivity and reproducibility as well as assessment of setup and calibration complexity for each instrument. Thus, results of the proposed study in Greenland are fundamental to engineering and scientific preparation for a proposed dual landing in 2018 of a NASA rover designed to explore and cache samples and a European Space Agency rover designed to drill down to depths of 2 meters.
Access to the proposed study site is possible year-round at reasonable cost due to the presence of a former U.S. military airbase with re-purposed buildings serving as the Kangerlussuaq International Scientific Support Facility. Continuous permafrost is present down to 300 meters depth with temperatures dropping to -3 degrees centigrade at a depth of about four meters, providing a relatively shallow and pristine setting for an instrumented study of reduced trace gases released by weathering and by microbial metabolism in super-permafrost bedrock and soil. There are mafic rock units and fracture zones within the proposed Greenland study site that are excellent targets for drilling Mars-analogue boreholes.