In 1971, data from the Mariner 9 probe first detected ice from the south pole of Mars, sparking a 50-year debate over whether ice flows or not.
Each time a flow interpretation emerged, it was quickly discarded with new observations. For 50 years, researchers have struggled to explain this immobile ice.
Now, a new paper led by Planetary Science Institute (PSI) senior scientist Isaac Smith has an answer: Ice, which is made of variable layers of material, can be held in place by those layers.
High-resolution images of Mars’ polar caps reveal complex layered structures. These caps are between 2 and 3 km thick and extend more than 1,000 kilometers along the Martian poles. These polar caps are composed mainly of water ice. Beneath the ice lies a complex landscape that includes steep slopes and cliffs.
Researchers had expected that ice flows could reach speeds of up to 1 meter per year in these regions, and even the most modest flow predictions predict flows of 10 centimeters per year. This rate of motion would be visible in images taken over a short period of time by modern missions, with their ability to resolve features as small as 1.2 to 2.4 meters. Long-duration flow should also be visible in other features such as moraines (or debris piles), depressions in frozen cliffs, and layer deformation. None of this is seen in any location on any of the polar caps.
Given the lack of observations supporting ice flow, as Smith puts it in a statement, “the question then becomes, why is the ice moving slower than predicted and how slow is it? We have an upper limit, So let’s test some hypotheses. In my article, I looked at four hypotheses to see if they could slow down the ice.”
LIKE OREO COOKIES
In a new paper published in the journal Icarus, Smith performs complex calculations for four different scenarios: 1) the ice is too cold to move, 2) impurities in the ice slow it down, 3) its homogeneous mixture of material slows the flow, 4) the ice is arranged in layers in a way that uniquely slows it down to an immeasurable flow. While all four ideas sounded possible, mathematical models showed that in the first three cases, the ice should still have moved observably and left evidence behind. Only in the latest layered landscape model was the ice fixed in place.
“The layers are similar to those used to make marshmallows or Oreos: stiff layers with soft layers in between. If you stack enough Oreos on top of each other and press, there will be some flow, but not as much as if you had a chopped Oreo cookie mix,” explains Smith. “The layered model can slow things down by several orders of magnitude, enough to match the observed motions (or lack thereof).”
As we build models that allow us to understand the diversity of glaciers in our solar system, we begin to see how the physics can be the same everywhere, but specific local conditions cause things to act very differently. It’s easy to imagine Mars as Earth-like, and perhaps it once was, but for the last billion years or so, Mars has had a unique, harsh climate that leaves very un-Earth-like characteristics for us. let us study them.
“Researchers since Percival Lowell have been considering the polar ice caps on Mars. Lowell even considered flowing ice and canals to help people living on Mars,” says Smith, referring to Lowell’s work at the turn of the century. XIX and early 20th century.
“We need to understand basic physical principles before we can say much more about what is happening on other planets. This is quite esoteric, very few people are interested in the dynamics of ice sheets on other planets, but many more people are interested. The history of ice on Mars is interesting. Without the right context, we can be wrong for decades. Getting it right means knowing which processes are active and which are not. I think this article brings us much closer to understanding why ice on Mars behaves the way it does. way he does it without moving,” he adds.
