New study challenges a key Martian water theory

When planning with crew Missions to Mars the keyword is “Follow the Water”. When astronauts land on the red planet in the next decade, they will need access to water to meet their basic needs.

Following the water is also crucial to our ongoing exploration of Mars and to learning more about its past. While all of the water on the surface of Mars now exists as ice (most of it trapped in the polar ice caps), it is now known that rivers, lakes, and an ocean covered much of the planet billions of years ago.

Determining where this water went is critical to learning how Mars underwent its historical transformation to become the dry and cold place it is today.

Almost 20 years ago, the ESAs Mars Express Orbiter made a tremendous discovery when it uncovered what appeared to be a massive deposit of water ice beneath the southern polar region. However, recent findings from a team of researchers at Cornell University suggest that the radar reflections from the South Pole Layered Deposit (SPLD) could be the result of geological stratification.

The research was led by Daniel Lalich, a research associate at the Cornell Center for Astrophysics and Space Science (CCASS). The paper that described their findings, titled Explain bright radar reflections beneath the south pole of Mars without liquid waterwas published on September 26 in natural astronomy.

Mysterious Layers

In 2004, the Mars Express orbiter discovered the SPLD using the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). While many astronomers have concluded that the radar bounce was the result of a 1.4-kilometer (0.89-mile)-thick formation of relatively pure water ice, there has since been an ongoing debate as to whether the SPLD is water ice or something else entirely.

For their study, Lalich and his colleagues ran computer simulations on the MARSIS data to investigate what might have produced the strong radar reflections.

As they explained in their article, radar reflections of this type are the result of liquid water on Earth, as evidenced by buried lakes like Lake Vostok beneath the East Antarctic Ice Sheet. But on Mars, the prevailing view has been that conditions are too cold for similar lakes to form.

To study this, Lalich and his colleagues used a one-dimensional modeling technique commonly used to interpret MARSIS observations. This consisted of simulation layers of four materials (atmosphere, water ice, carbon dioxide [CO2] ice and basalt) and assign a corresponding permittivity to each layer.

This describes the interaction between a material and how electromagnetic radiation penetrates it instead of being reflected from it. In the end, they found that three-layer simulations (two layers of CO2 ice separated by a layer of dusty ice) produced reflections that were as bright as the MARSIS observations.

This effectively showed that geological strata could explain the SPLD readings without the presence of water or other rare materials. As Lalich explained in a recent article Cornell Chronicle Press release:

“I used layers of CO2 embedded in water ice because we know it’s already abundant near the surface of the ice cap. In principle, however, I could have used layers of rock or even particularly dusty water ice and would have come to similar results. The point of this paper is really that the composition of the basal layers is less important than layer thicknesses and spacing.”

No need for H2O?

From their modelling, the team also found that the thickness and spacing of the layers have a greater impact on reflectivity than their respective compositions. While this does not necessarily mean that there is no liquid water beneath the south pole of Mars, the results suggest that the MARSIS readings can be reproduced in the absence of water.

This builds on research conducted in 2021 (to which Lalich contributed) which showed that a class of minerals common on Mars (smectite) could produce a reflection similar to that observed by MARSIS under the right conditions .

Given its importance for future missions and for understanding the evolution of Mars, it is vital that scientists determine where water is (and isn’t) on Mars. The presence of liquid water beneath the polar cap could also have important implications for its age, the internal heating of Mars, and the evolution of the planet’s climate over recent geologic periods.

The same applies to the many other suspected underground lakes that have been discovered in recent years. As Lalich has indicated, he and his colleagues are not yet ruling out the possibility of liquid water:

“If there is liquid water, maybe there is life, or maybe we could use it for future human missions to Mars. None of our work disproves the possible existence of liquid water down there. We just think the interference hypothesis is more consistent with other observations. I’m not sure anything other than an exercise could definitively prove either side of this debate right or wrong.”

This article was originally published on universe today by Matt Williams. Read the original article here.