When contemplating Martian ice, our minds typically gravitate toward the poles, where it’s visually observable via probes and even ground-based telescopes. However, access to the polar regions is difficult, especially given the limitations on exploration in those areas due to the risk of biological contamination.
Scientists have long hoped to locate water closer to the equator, which would make it more readily accessible to researchers. In Mars’ mid-latitudes, there are regions resembling glaciers blanketed by thick layers of dust and rock. Do these formations truly harbor vast water reserves near where humans might first set foot on the Red Planet? Possibly, according to a new paper by M.A. de Pablo and co-authors, recently published in the journal Icarus.
The key to deciphering this might lie with a small volcanic island in Antarctica. Known as Deception Island, this volcano covered the surrounding massive glaciers with ash and dust following a series of eruptions in the 60s and 70s. The authors suggest they’ve identified a Martian volcano with a similar history, named Hecates Tholus.
Hecates Tholus is an ancient shield volcano on Mars that shares many characteristics with Deception Island’s volcano. Since it’s established that ice exists beneath the debris on Deception Island, this could imply that similar formations might be present under the debris surrounding Hecates Tholus.
On Mars, there is compelling evidence for glacial ice, rather than just loose rocks or even rocks loosely bound by a small amount of ice. Firstly, there are crevasses. Any explorer will tell you how hazardous these formations are on Earth, but the key feature of crevasses on Deception Island is that they are visible from orbit, particularly near the glacier’s “headwall”—the steep, nearly vertical cliff face marking the glacier’s highest point. Similar features are visible from orbit at Hecates Tholus, and such distinct, visible crevasses would not be apparent if only rock lay beneath them. Specifically, these crevasses indicate that a solid ice mass is still moving beneath the surface debris of the volcano.
Another undeniable piece of evidence is the presence of bergschrunds. These are characteristic deep cracks formed at the very top of a glacier. All bergschrunds are technically a form of crevasse, though they are significantly larger and arise from a much more specific process than typical examples. This process is the separation of moving ice from stationary ice. Some examples of bergschrunds near Hecates Tholus stretch up to 600 meters long and are clear indicators that, at some point, active ice movement was occurring.
Yet another supporting factor is the bulldozer effect—or more accurately, the presence of “push moraines” at the base of the valleys on both Deception Island and Hecates Tholus. As they advance, glaciers act like bulldozers, pushing massive stones ahead of them and leaving behind hummocky terrain. Similar landforms to those found on Deception Island are again visible around Hecates Tholus, suggesting that an active glacier existed in that area at one time.
So, if these glaciers truly exist, how have they managed to persist for millions of years without sublimating away? The authors propose a two-stage process. Initially, when the crevasses formed, some water did sublimate, but those openings were subsequently covered by dust, shielding the newly exposed water from further sublimation. This ultimately resulted in the shallow “furrows” we observe on Mars, rather than true crevasses.
One obvious question for those closely following Mars exploration is why SHARAD hasn’t detected anything there. If a subsurface glacier exists near the equator, the ground-penetrating radar aboard the Mars Reconnaissance Orbiter should certainly have picked up a signal. After all, we have repeatedly reported on this in other Martian regions (and sometimes had to revise those findings). SHARAD radar physics performs poorly on the steep slopes of volcanoes, making it hard to gain a clear picture of what lies beneath the dust and debris. For a truly better understanding, we will need samples gathered from Earth, either by robots or humans.
But the paper carries another, unstated implication. If enormous glaciers are indeed hiding near Hecates Tholus on Mars, perhaps numerous other glaciers are concealed near other massive volcanoes. Article IX of the 1967 Outer Space Treaty mandates the exploration of other solar system bodies to avoid “harmful contamination” of celestial bodies. Many have interpreted this clause as requiring explorers to steer clear of the Martian poles, where evidence of abundant water exists. If water turns out to be widespread across Mars, buried under volcanic debris, does this mean those areas are also off-limits to researchers?
Only time will reveal the answer to this question—and we may never know for certain if water is present around these volcanoes unless we dispatch explorers there, as there’s only so much we can achieve remotely. There are proposals for missions that could settle this debate, such as FlyRADAR, but for now, we must await definitive confirmation on whether Martian volcanoes are indeed glaciated—and perhaps, for the moment, observe a similar volcano in our own vicinity.
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