The remains of a glacier have been found near the Martian equator, suggesting that some form of water could still exist in a region on the red planet where humans may one day land.
The ice mass is no longer there, but scientists spotted telltale remains among other mineral deposits near Mars' equatorial region. The deposits there usually contain light-colored sulfate salts.
When scientists took a closer look, they recognized the features of a glacier, including ridges called moraines — debris deposited or pushed by a moving glacier. The research team also spotted crevasse fields, or deep wedge-shaped openings that form inside glaciers.
The findings were shared Wednesday at the 54th Lunar and Planetary Science Conference in The Woodlands, Texas.
"What we've found is not ice, but a salt deposit with the detailed morphologic features of a glacier," lead study author Dr. Pascal Lee, a senior planetary scientist with the SETI Institute and the Mars Institute, said in a statement.
"What we think happened here is that salt formed on top of a glacier while preserving the shape of the ice below, down to details like crevasse fields and moraine bands."
The researchers believe the glacier was 3.7 miles (6 kilometers) long and 2.5 miles (about 4 kilometers) wide, with an elevation between 0.8 to 1.1 miles (1.3 to 1.7 kilometers).
Volcanic activity creates protective layer
Scientists have an idea of how the imprint of the glacier came to be, based on evidence of volcanic material in the region. When mixtures of volcanic ash, lava and volcanic glass called pumice react with water, a hard, crusty salt layer can form.
"This region of Mars has a history of volcanic activity. And where some of the volcanic materials came in contact with glacier ice, chemical reactions would have taken place at the boundary between the two to form a hardened layer of sulfate salts," said study coauthor Sourabh Shubham, a doctoral student of geology at the University of Maryland, College Park, in a statement.
"This is the most likely explanation for the hydrated and hydroxylated sulfates we observe in this light-toned deposit."
Geologically young surface ice near equator
The volcanic material likely eroded over time, revealing the salty layer that captured an imprint of the glacier ice and its distinctive features, said study coauthor John Schutt, a geologist at the Mars Institute and an icefield guide in the Arctic and Antarctica.
Mars has a thin atmosphere, which allows space rocks to collide regularly with the planet's surface. But the fine, detailed features of the glacier still remain largely undisturbed in the salt deposit, which leads researchers to believe it's relatively "young."
The study authors said they think the glacier existed during the Mars Amazonian geologic period, which began 2.9 billion years ago and remains ongoing.
"We've known about glacial activity on Mars at many locations, including near the equator in the more distant past. And we've known about recent glacial activity on Mars, but so far, only at higher latitudes," Lee said. "A relatively young relict glacier in this location tells us that Mars experienced surface ice in recent times, even near the equator, which is new."
The researchers don't know if any ice remains beneath the deposit.
"Water ice is, at present, not stable at the very surface of Mars near the equator at these elevations," Lee said. "So, it's not surprising that we're not detecting any water ice at the surface. It is possible that all the glacier's water ice has sublimated away by now. But there's also a chance that some of it might still be protected at shallow depth under the sulfate salts."
Potential for shallow ice pockets
During the study, the team also looked at ancient ice islands called salars in Bolivia's Altiplano salt flats in South America. Blankets of salts have protected old glacier ice from melting or evaporating, leading the researchers to think that a similar scenario might have occurred on Mars.
Next, the researchers want to determine if any ice remains from the glacier, and if so, how much is present at shallow depths beneath the salt deposits. If this particular salt deposit is protecting ice, it's possible that other pockets of ice exist nearby.
Orbiters circling the planet have shown deposits of ice at the frigid Martian poles, but if water in any form exists at the warmer equatorial lower latitudes, it could have implications for our understanding of the red planet's history and potential habitability — and future exploration by humans.
"The desire to land humans at a location where they might be able to extract water ice from the ground has been pushing mission planners to consider higher latitude sites," Lee said. "But the latter environments are typically colder and more challenging for humans and robots. If there were equatorial locations where ice might be found at shallow depth, then we'd have the best of both environments: warmer conditions for human exploration and still access to ice."
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