For anyone hoping that life will soon be found on Mars, there is disappointing news – “polar lakes” may be nothing more than just frozen clay.
It all began in 2018 when a team led by Roberto Orosei of Italy’s Istituto Nazionale di Astrofisica claimed that they discovered evidence of subsurface lakes beneath the Martian South Pole. They made the discovery by using a radar instrument on board the European Space Agency’s Mars Express orbiter. The radar signals that seemingly came from underneath the polar cap were incredibly bright which could have indicated liquid water. And with the possibility of liquid water came the discussions of potential life inhabiting the Red Planet.
While this was certainly exciting news, recent studies have claimed that the radar signals may have been picking up frozen clay instead of liquid water. First, the scientists had to figure out how much heat would be needed for water to remain in liquid form underneath the surface of the planet.
Jeffrey Plaut from NASA’s Jet Propulsion Laboratory (JPL) and Arizona State University doctoral student Aditya Khuller (who was interning at JPL) studied 44,000 radar echoes over a span of 15 years that were taken at the base of the southern polar cap by the Mars Advanced Radar for Subsurface and Ionospheric Sounding (MARSIS). Interestingly, they found dozens more bright radar reflections similar to the one in 2018. Additionally, many of the signals were captured close to the surface of the planet where water couldn’t have been in liquid form. This certainly raised questions as to what was causing the radar signals.
At that point, two different groups of scientists looked at the radar signals in greater detail and found that they could have been caused by several other factors, such as saline ice, metal-bearing minerals, and clay. Isaac Smith from York University in Toronto went a step further by analyzing smectite – this is a type of clay that looks like a normal rock but was created by liquid water and is found all over the Martian surface. He put frozen liquid nitrogen on the smectite to make it similar to how it would be found at the South Pole of Mars and then measured its radar signal. Incredibly, his results matched almost perfectly to the radar signals found on Mars.
He then made sure that there was in fact smectites around the Martian South Pole and he was correct. This experiment proved that smectite can make radar reflections and it is found in the exact area where the subsurface “polar lakes” were thought to have been located.
On the other hand, it’s still unconfirmed whether the radar signals were picking up liquid water beneath the surface or if it was just frozen clay. The only way we’ll know for certain is to dig through miles of ice. “In planetary science, we often are just inching our way closer to the truth,” Plaut noted, adding, “The original paper didn’t prove it was water, and these new papers don’t prove it isn’t. But we try to narrow down the possibilities as much as possible in order to reach consensus.”