Modern glacial remains found near the Martian equator suggest water ice may be present at low latitudes today

A relict glacier near the equator of Mars. Image credit: NASA MRO HiRISE and CRISM false color composite/Lee et al. 2023

In a landmark announcement at the 54th Lunar and Planetary Science Conference in The Woodlands, Texas, scientists unveiled the discovery of a relic glacier near the equator of Mars. Located in the eastern Noctis Labyrinthus at coordinates 7° 33′ S, 93° 14′ W, this finding is significant because it indicates the recent presence of surface water ice on Mars, even near the equator. This discovery raises the possibility that ice may still be present at shallow depths of the area, which could have significant implications for future human exploration.

The surface feature identified as “Relic Glacier” is one of many light tone deposits (LTDs) found in the region. Typically, LTDs are mostly composed of light-colored sulphate salts, but this deposit also shows many features of a glacier, including crevasse fields and moraine bands. The glacier is estimated to be 6 kilometers long and up to 4 kilometers wide, with a surface elevation of +1.3 to +1.7 kilometers. This discovery suggests that Mars’ recent history may have been more watery than previously thought, which could have implications for understanding the planet’s habitability.

“What we found is not ice but a salt deposit with the detailed morphological features of a glacier. What we think happened here is that salt formed on a glacier while the shape of the underlying ice was preserved in minute detail—crevasse fields and moraine bands,” said Dr. Pascal Lee, a planetary scientist at the SETI Institute and at the Mars Institute and lead author of the study.

The presence of volcanic material covering the region suggests how the sulfate salts may have formed and preserved an underlying glacial imprint. When freshly erupted pyroclastic materials (mixtures of volcanic ash, pumice, and hot blocks of lava) come in contact with water ice, sulfate salts, such as those commonly found in Mars’ bright deposits, can form and build up into a hardened, crusty layer of salt.

“This region of Mars has a history of volcanic activity. And where some of the volcanic materials came into contact with glacial ice, chemical reactions would have taken place at the boundary between the two to form a hardened layer of sulfate salts,” explains Sourabh Shubham, a graduate student in the University of Maryland’s Department of Geology and co- author of the study. “This is the most likely explanation for the hydrated and hydroxylated sulfates we observe in this light-toned deposit.”

Over time, as erosion removed the covering volcanic material, a crustal layer of sulfates was exposed, reflecting the underlying glacial ice, which would explain why a salt deposit is now visible, with features unique to glaciers such as fissures and moraine bands.

Interpretation of the features of the relict glacier. Photo credit: Lee et al. 2023

“Glaciers often exhibit distinctive types of features, including marginal, splaying, and tic-tac-toe fissure fields, as well as thrust moraine bands and foliation. We see analogous features in this light-toned deposit in shape, location, and extent. It’s very intriguing,” said John Schutt, a geologist at the Mars Institute, a veteran ice field guide in the Arctic and Antarctic and a co-author of this study.

The subtle features of the glacier, associated sulfate salt deposits, and overlying volcanic material are all very sparsely impact-cratered and must be geologically young, probably of Amazonian age, the last geological period to encompass modern Mars. “We have known of glacial activity on Mars in many places, 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. A relatively young relic glacier at this location tells us that Mars has had surface ice very recently, even near the equator, which is new,” Lee said.

It remains to be seen whether there is still water ice beneath the bright deposit or whether it has completely disappeared. “Water ice is currently not stable on the surface of Mars near the equator at these altitudes. It is therefore not surprising that we do not find any water ice on the surface. It is possible that all of the glacier’s water ice has sublimated away by now. But there is also the possibility that part of it is still protected at a shallow depth under the sulphate salts.”

The study draws an analogy to the old ice islands on salt lake beds or salars of the Altiplano in South America. There, old glacial ice has remained protected from melting, evaporation, and sublimation under blankets of light-colored salts. Lee and his co-authors use a similar situation to explain how sulfate salts on Mars might be able to provide protection for otherwise sublimation-prone ice at low latitudes on the planet.

If there is still water ice on Mars at shallow depths, it would have implications for science and human exploration. “The desire to land humans in a place where they might be able to extract water ice from the ground has prompted mission planners to consider locations at higher latitudes. But the latter environments are usually colder and more challenging for both humans and robots. If there were equatorial locations where ice could be found at shallow depths, then we would have the best of both environments: warmer conditions for human exploration and still have access to ice,” Lee said.

But Lee warns that more work needs to be done: “We now need to determine if and how much water ice may actually be present in this relict glacier, and if other bright deposits may also have or have had ice.” rich substrates.”

More information:
Pascal Lee et al, A relict glacier near the Martian equator: evidence for recent glaciation and volcanism in the eastern Noctis Labyrinthus (2023)

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