Searching for Liquid Water in the Martian Deep with TH2OR
Abstract
The "holy grail" of planet exploration is the quest for life. This quest has been framed around "follow the (liquid) water", with the implication that seeking liquid water is tantamount to seeking habitable environments. For Mars, pure liquid water is generally only stable in the deep subsurface, at depths of kilometers. Here, we will describe (i) how we can use transient electromagnetic techniques (TEM) to sense liquid groundwater in the Martian subsurface and (ii) discuss the capabilities of the TH2 OR (Transient H2 O Reconnaissance) TEM instrument, which is currently being developed at JPL - with a targeted capability to detect liquid groundwater in the Martian subsurface down to depths of several kilometers while keeping payload mass and power small. Our TEM approach is different from radar soundings as it is not sensitive to the dielectric constant but rather to electric conductivity and allows much deeper penetration down to aquifer depths of ~1-10 km due to the lower frequencies that are being used (~Hz-kHz for EM versus ~MHz for radar). EM exploits the fact that only slightly-saline water has an electric conductivity orders-of magnitude greater than dry rock. On Mars, we expect especially highly-saline waters due to the much longer residence time of groundwater than on the geologically and hydrologically much more active Earth. Moreover, as the Martian crust is expected to be much drier than the Earth's crust, we expect much greater contrast ratios in electric conductivity between overburden (crustal part above aquifer) and a putative aquifer on Mars than on the Earth. These "Martian TEM advantages" allow us to sound with TH2 OR down to depths of kilometers in order to infer the depth, thickness, and also salinity of liquid subsurface water. Salinity, especially in combination with information on local geothermal gradients, can hence also allow us to indirectly estimate its chemical composition. The ability to characterize the water chemistry to some degree is a particularly important feature of TEM sounding, which other methods generally lack. This opens the possibility to use TH2 OR to detect and characterize the habitability of deep subsurface environments on modern-day Mars.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFM.P44B..02B
- Keywords:
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- 1829 Groundwater hydrology;
- HYDROLOGY;
- 5215 Origin of life;
- PLANETARY SCIENCES: ASTROBIOLOGY;
- 6225 Mars;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS;
- 6297 Instruments and techniques;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS