Mars Groundwater is a No Show

Jan 26, 2022 | Daily Space, Mars, Opportunity

IMAGE: A view of Mars’ south pole. Research led by The University of Texas at Austin found that a 2018 discovery of liquid water under the Red Planet’s south polar cap is most likely just radar reflecting from volcanic rock. CREDIT: ESA/DLR/FU Berlin

While the cold weather pushes through my part of the midwest, I’m reminded of the landing of the Mars Exploration Rover Opportunity back in 2004. That day it was warmer on Mars where Opportunity landed than it was where I worked in the city of Boston. I was envious of that warm rover and became very close friends with its distant cousin, my electric space heater.

While we think of Mars as a sub-freezing desert, the truth is summertime temperatures can soar into the 70s. It’s not the temperatures that prevent water from flowing on the red planet; it is the lack of atmosphere. Without the push back of air, water molecules will happily go from frozen ice to humidity raising gas in a single step called sublimation.

Scientists held out hope, however, that groundwater could still exist beneath the surface. Not ice; water. In 2018, this hope was thought to be confirmed as reality when radar returns showed a region of high reflectivity under Mars’s ice-covered south pole. In general, radar reflects extremely well off water, and we know that sub-glacial conditions can allow liquid water here on Earth, but sometimes when you see smoke, there is just a smoke machine and no actual fire.

In this case, the strong radar returns came from a region that detailed calculations said probably shouldn’t actually have water. Mars isn’t Earth, and what makes sense here, doesn’t apply there. When a different team of researchers simulated what other regions of Mars would look like in radar if covered in ice, they realized that volcanic plains, with their solidified iron-rich lava, can reflect in ways that look just like what was seen at the south pole.

This research was led by Cyril Grima and appears in Geophysical Research Letters. Grima’s colleague Isaac Smith reminds us: Science isn’t foolproof on the first try. That’s especially true in planetary science where we’re looking at places no one’s ever visited and relying on instruments that sense everything remotely.

Space is hard, but it is really amazing that while we can’t yet explore Mars in person, we can explore it with robots, radar, and so much more.

More Information

AGU press release

UTA press release

The Basal Detectability of an Ice-Covered Mars by MARSIS,” C. Grima, J. Mouginot, W. Kofman, A. Hérique, and P. Beck, 2022 January 24, Geophysical Research Letters

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