There has been a renewed discussion on the possibility of liquid water existing on modern-day Mars due to recent radar measurements made beneath the Martian south polar layered deposit (SPLD). However, unlike Earth, the temperature is too low under Martian ice to sustain or produce meltwater.
Researchers from Cornell University have offered a clear, thorough, and less spectacular explanation for the bright radar reflections that were first thought to be liquid water beneath Mars’ south pole’s ice cap.
According to their models, radar signals can constructively interfere with one another due to minute fluctuations in water ice layers that are too small for ground-penetrating radar equipment to detect.
Such interference can result in reflections with intensities and variability that correspond with observations made thus far, both in the region thought to contain liquid water and across the so-called south-polar layered deposits.
Daniel Lalich, a research associate at the Cornell Center for Astrophysics and Planetary Science, said, “I can’t say it’s impossible that there’s liquid water down there, but we’re showing that there are much simpler ways to get the same observation without having to stretch that far, using mechanisms and materials that we already know exist there. Just through random chance, you can create the same observed signal in the radar.”
Robotic explorers, such as NASA’s Perseverance rover, have uncovered ample evidence that water once flowed on the surface of ancient Mars, notably at a former river delta. In 2018, the science team of the European Space Agency-led Mars Express spacecraft announced that they had found a lake buried beneath the south polar cap, thanks to their use of a radar sensor that can probe below the surface to find water ice and potentially undiscovered aquifers.
The ramifications were profound: microbiological life may exist anywhere in liquid water.
The same brilliant would probably indicate a subglacial lake on Earth, but Mars has completely different pressure and temperature circumstances.
Lalich has previously demonstrated using simpler models that bright radar signals could be produced even in the absence of liquid water, but he said it was likely erroneous to assume that layers of frozen carbon dioxide were beneath the ice cap.
He said that the new research fills in the radar interference theory gaps with more accurate modeling and provides a more comprehensive story. The thousands of randomly produced layering scenarios altered the composition and spacing of the ice layers in ways expected across tens or hundreds of km, and they were solely based on conditions known to occur at the Martian poles.
Lalich said, “This is the first time we have a hypothesis that explains the entire population of observations below the ice cap without having to introduce anything unique or odd,” Lalich said. “This result where we get bright reflections scattered all over the place is exactly what you would expect from thin-layer interference in the radar.”
While not ruling out the potential for some future detection by more capable instruments, Lalich said he suspects the story of liquid water and potential life on the red planet ended long ago.
“The idea that there would be liquid water even somewhat near the surface would have been fascinating,” Lalich said. “I just don’t think it’s there.”
Journal Reference:
- Daniel Lalich, Alexander Hayes et al. Slight variations in ice composition and layer thickness explain bright reflections below martian polar cap without liquid water. Science Advances. DOI: 10.1126/sciadv.adj9546