Every morning during the Martian spring and summer, a thin and extremely long cloud emerges, only to disappear again. The wispy formation appears near the volcano Arsia Mons and gradually elongates until it reaches over 1,000 miles—about the distance from New York to Kansas City as the crow flies—before dissipating. This cycle then repeats for several months.

Since it was first recorded by a probe in 2018, scientists have been unable to find a plausible explanation for the existence of this cloud, often referred to as the Arsia Mons Elongated Cloud (AMEC). Until now. Recently, researchers successfully modeled the cloud’s formation for the first time, their results suggesting that it may be driven by a physical process that has never been directly observed in any planet's atmosphere.

"We found that we needed to include some exotic physics… physics that, while included in textbooks, is treated as theoretical and usually thought not to happen in nature. It certainly hasn’t been seen in action before," Jorge Hernández-Bernal, a planetary scientist at Paris’ Sorbonne Université and lead author of the study, said in a press release. "Once we included this physics in our simulations, the AMEC emerged just as we hoped.”

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Barnes Ice Cap sits on the central plateau of Baffin Island, in the Canadian Arctic. It is the last surviving fragment of the Laurentide Ice Sheet, the largest of the Pleistocene ice sheets, which at its peak buried most of Canada under two miles of ice and locked away around 80 meters of sea level. That remnant has now yielded direct physical evidence that ice sheets might have reversed their retreat and started to grow again thousands of years ago.

In a recent Science study, researchers show that the Laurentide reached its smallest size about 3,600 years ago, then started re-expanding roughly 2,000 years ago, which the team interprets as the opening move of the next glaciation. Apparently, this brand-new ice age was on its way until about 1960, when human-caused climate warming reversed it.

Frozen to the bed

“Barnes is the last remaining piece of one of the domes of the Laurentide Ice Sheet,” says Nicolás Young, a geologist at Columbia University's Lamont-Doherty Earth Observatory and lead author of the study. As that enormous dome thinned through the Holocene, its margin withdrew up onto Baffin Island, and what's left today is the deflated core of something that was once two miles thick. The reason Barnes can testify about its own history, Young explains, comes down to the temperature at its base.

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