Credit: Planetary Science Institute Blue marks in the Martian South Polar Region that were previously thought to be indicative of subsurface water may now indicate other subsurface materials. Credit: USGS Astrogeology Science Center at Arizona State University, INAFA new paper suggests that the liquid water lakes discovered beneath Mars' south pole might not have been as dry as previously thought.Scientists had previously detected radar reflectivity areas using the Mars Advanced Radar for Subsurface and Ionosphere sounding (MARSIS), an instrument aboard the European Space Agency’s Mars Express orbiter. They believed these were lakes deep below the surface ice.However, this may not be true according to a paper "Strong MARSIS radar reflections from the Base Martian South Polar Cap might be due Conductive Ice or Minerals", published in Geophysical Research Letters. Nathaniel Putzig, Senior Scientist at PSI, is the author. Lead author is Carver J. Bierson, Arizona State University.To explain the results of MARSIS observations, it is not necessary that liquid water be invoked at the base the polar caps. Putzig suggested that clays, some metal minerals and salty ice are possible alternatives.Lead author Bierson stated that the team wanted to look at other materials than liquid water in order to determine if they could produce bright reflections. Salty ice and conductive minerals are at the base the ice sheets are less visible, but are closer to the extreme cold temperatures at Mars poles."Because water, especially in liquid form, is so essential to the survival of life, it is vital that astrobiological researches seek out its presence on Mars in the present or in the past. Putzig stated that it is essential to consider all other possible detections of liquid water in order to make scientific progress.MARSIS detects the subsurface reflected echo and surface reflections when a radar beam is directed towards Mars' surface. The electrical properties of underground liquid water are very different from those found in surrounding rocks or ice, and they will reflect very strongly.Earlier MARSIS analyses of subsurface radar reflections primarily concentrated on electrical permittivity. Permittivity is a control over the speed of radio waves in a material (fastest within vacuum, slowest in ice and slower still in rock, and less power for reflected waves). To explain the MARSIS results, the new paper examines electrical conductivity.According to the paper, previous research had reported strong radar reflections under Mars' south-polar ice sheet. This radar reflection was seen as liquid water due to its brightness. The contrast between electric conductivity and dielectric permittivity can make a radar reflection bright. Prior research only looked at contrasts in dielectric permistivity. The reflection's brightness could also be explained by differences in the electric conductivity of materials. This could be caused by clays, metal-bearing mineral, or saline under the polar glacier."Electrical conductivity is interrelated with permittivity. Putzig stated that most previous assessments of the power subsurface radar reflections have focused on permittivity rather than conductivity when assessing reflective properties of materials. This led to previous workers concluding that liquid water, which was expected to be liquid at temperatures and pressures 1.5 km below Mars' south pole ice cap, is the best explanation for radar reflectivity. The paper shows that conductivity can play an important role in some materials and therefore, this paper offers a viable alternative explanation.Continue exploring Explore more Study Mars' underground water signalsC. J. Bierson et. al., Strong MARSIS radar Reflections from Base of Martian South Polar Cap could be due to Conductive Ice or Minerals. Geophysical Research Letters (2021). Information from Geophysical Research Letters C. J. Bierson et. al. Strong MARSIS Radar Refractions from the Base Martian South Polar Cap could be due to Conductive Ice or Minerals. (2021). DOI: 10.1029/2021GL093880
