Geophysical Investigations of the Interior of Mars, Emphasizing the Detection, Characterization, and History of Groundwater, 15-9428

Principal Investigator
Robert E. Grimm

Inclusive Dates:  10/01/04 - Current

Background - The NASA Mars Exploration Program Assessment Group (MEPAG) has rated the detection and characterization of subsurface, liquid water as one of the highest exploration objectives. Low-frequency electromagnetic (EM) sounding has been a principal geophysical tool in terrestrial groundwater investigations for decades and is the best choice for detection of liquid water on Mars.

Approach - The principal goals of this investigation are to develop concepts for EM instruments and EM-centered Scout missions for Mars. Additional work will focus on the history of groundwater on Mars, particularly using recently acquired data sets.

Quantitative requirements for detecting groundwater on Mars using both passive and active low-frequency EM sensors will be developed. Passive systems will be given priority because they exploit ambient EM energy from natural sources and therefore can be low mass and cost. Active systems use a transmitter and therefore can achieve higher signal-to-noise, but over a more limited depth range. EM methods will be tested in a variety of terrestrial Mars-analog environments. With regard to the history of groundwater on Mars, the research team will first extend saturated-flow models to full spherical geometry and further explore the conditions of recharge and crustal heterogeneity that permit development of the outflow channels. The team will further determine whether relationships among different kinds of fluvial features on Mars can be interpreted in terms of progressive global cooling and surface dessication. This latter task will require the development of additional software tools to utilize the recent THEMIS visible and infrared image database.

Accomplishments - The team studied the possibility of incorporating low-frequency EM sensors on the Mars Mobile Science Laboratory (MSL), but determined that such an experiment would likely be judged out of scope for this mission. However, this work contributed to an invitation by JPL to be principal investigator of a high-frequency EM subsurface investigation proposed to MSL. Together with personnel from the Center for Nuclear Waste Regulatory Analyses, the team performed EM surveys near Yucca Mountain, Nevada, and determined that this area was not a suitable Mars analog because of the high ground conductivity. The team published an innovative concept for ancient groundwater dynamics on Mars in Geophysical Research Letters and received the cover illustration of that journal. Also the team developed the necessary THEMIS software tools and began mapping relationships between valley networks and outflow channels on Mars.

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