Michelle Starr
What scientists think are lakes of liquid water lurking under the ice cap at Mars’ south pole may be an ordinary layer of ancient rock. New investigations have revealed that the bright radar signal thought to be groundwater on the Red Planet may also be formed by geological stratification. This isn’t a definitive conclusion yet, but it does reveal that we need stronger evidence before we can pinpoint what’s lurking beneath the surface.
‘NOT WATER’
“We show here that similar reflections can occur as a natural consequence of lamellar formation, not to mention any liquid water or other rarefied substances,” says a research team led by Dan Lalich, an astronomer at Cornell University. combined with other recent studies, it questions the possibility of finding liquid water beneath the south polar stratified sediment (SPLD).”
This enigmatic signal was first detected several years ago in radar data collected by the European Space Agency’s Mars Express satellite probe. There, scientists detected an unusually reflective layer of material buried beneath Mars’ south polar ice cap. Subsequent searches revealed subterranean layers that glowed brighter; this revealed that whatever the first layer found, it was by no means unique.
Even more excitingly, bright strata like these were also found right here on Earth, and were also buried under the ice at the South Pole. These are sub-ice lakes, such as Lake Vostok, that form a network of liquid deposits under the Antarctic ice. This led scientists to the conclusion that similar liquid deposits may exist on Mars. There’s only one problem: Mars is thought to be too cold for liquid water to exist, even under the pressure of ice sheets, and to have a low freezing point due to the presence of various salts.
WHAT DO LAYERS CONSIST OF?
So, what are these bright spots? To investigate this, Lalich and his colleagues conducted various simulations using a layer of four materials known to occur on Mars. Ground penetrating radar works by bouncing radio waves over an object or surface. How long and how strong these radio waves are reflected back reveals the properties of materials found under a planet’s surface; however, it does not indicate what these materials are.
The researchers created layers of mimicked water ice, carbon dioxide ice, basalt, and atmosphere in varying configurations and thicknesses, all of which contain properties that reflect radar waves in specific ways. Next, they resolved the issue of what signals these configurations would generate. And they arrived at something as bright as the Mars Express observations: a layer of dusty water ice sandwiched between two layers of carbon dioxide ice.
“I used layers of CO2 (carbon dioxide) embedded in the water ice because we already know it exists in large quantities near the surface of the ice sheet,” explains Lalich. . The purpose of this article is to show that, in fact, the composition of the base layers is less important than the layer thicknesses and their separation.”
THERE ARE OTHER SUGGESTIONS
This is not the only proposition that the glowing signal could be produced by anything other than liquid water. Last year, a team of researchers discovered that frozen clays produce the same level of radar luminosity, and earlier this year another team cited volcanic rocks (which are abundant on Mars) as the source. The water explanation seems to be far from probable when including layers of rock and/or ice that seem more consistent with what we know about Mars.
This may be embarrassing because the past and perhaps present presence of liquid water on Mars will have some impact on the planet’s habitability and future crewed mission flights to the Red Planet. On the other hand, it may be the case that we will never know for sure.
“None of the research we’ve done refutes the possible presence of liquid water there,” says Lalich. I’m not sure anything outside of practice can definitively prove either side of this argument ‘right’ or ‘wrong’.”
Given the depth of the strata, the distance to Mars, and the difficulty of getting things there (especially heavy drilling rigs), it’s unlikely to happen in the near future.
The team’s research was published in the journal Nature Astronomy.
Original article Science Alert taken from the website. (Translated by Tarkan Tufan)