Equatorial relict glacier uncovered on Mars

The preservation of water ice at low depths and low latitudes on Mars would have significant implications for both scientific research and human exploration.

During the 54th Lunar and Planetary Science Conference held in The Woodlands, Texas, scientists announced a groundbreaking discovery of a relict glacier located near the equator Mars. This glacier is located in eastern Noctis Labyrinthus at coordinates 7° 33′ S, 93° 14′ W, and its discovery is a significant indication of the presence of surface water ice on Mars in recent history, even close to the equator. This finding also suggests the potential existence of ice at shallow depths in the region, which could have crucial implications for future human exploration.

The surface feature identified as a “relict glacier” is one of many light-toned deposits (LTDs) found in the region. Typically, LTDs consist mainly of light sulfate salts, but this deposit also shows many of the characteristics of a glacier, including fissure fields and moraine bands. The glacier is estimated to be 6 kilometers long and up to 4 kilometers wide, with a surface height 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 habitability of the planet.

“What we have 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 top of a glacier at the same time as that the shape of the ice underneath was preserved, down to details like fissure fields and moraine bands,” said Dr. Pascal Lee, a planetary scientist at the SETI Institute and the Mars Institute and lead author of the study.

The presence of volcanic materials covering the region suggests how the sulfate salts could have formed and preserved the imprint of a glacier below. When freshly erupted pyroclastic materials (mixtures of volcanic ash, pumice, and hot lava blocks) come into contact with water ice, sulfate salts like those that commonly make up Mars’ bright deposits can form and build up into a hardened, crusty salt layer.

Interpretation of “Relict Glaciers” features. Credit: Pascal Lee

“This region of Mars has a history of volcanic activity. And where some of the volcanic material came into contact with glacial ice, chemical reactions would have occurred 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-colored deposit.”

Over time, with erosion removing the overlying volcanic materials, a crusted layer of sulfates that mirrored the glacial ice beneath was exposed, which would explain how a salt deposit is now visible and presents features unique to glaciers, such as crevasses and moraine bands.

“Glaciers often display distinctive types of features, including marginal, scattered fissure fields and fissure fields, and also encounter moraine bands and foliation. We see analogous features in this bright deposit in shape, location and scale. It’s very exciting,” said John Schutt, a geologist at the Mars Institute, experienced Arctic and Antarctic ice field guide and co-author of this study.

The fine scales of the glacier, its associated deposits of sulfate salts, and the overlying volcanic materials are all very sparsely cratered by impacts and must be geologically young, probably of Amazonian age, the most recent geological period that includes modern Mars. “We’ve known of glacial activity on Mars in many places, including near the equator for a long time. And we’ve known of recent glacial activity on Mars, but so far only at higher latitudes. A relatively young relict glacier at this location tells us that Mars has experienced surface ice in recent times, even near the equator, which is new,” Lee said.

It is not yet known whether water ice is still preserved under the light deposit or whether it has disappeared completely. “Water ice is not currently stable on the very surface of Mars near the equator at these altitudes. So it is not surprising that we do not detect any water ice at the surface. It is possible that all the glacial water ice has sublimated away now. But there is also a chance that some of it is still protected at shallow depth beneath the sulfate salts.”

The study draws an analogy with the ancient ice islands on salt lake beds or salars in the Altiplano in South America. There, ancient glacial ice has remained protected from melting, evaporation and sublimation under blankets of bright salts. Lee and his co-authors hypothesize a similar situation to explain how sulfate salts on Mars might offer protection to otherwise sublimation-vulnerable ice at low latitudes on the planet.

If water ice is still preserved at shallow depths at a low latitude on Mars, 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 led mission planners to consider locations at higher latitudes. But the latter environments are typically colder and more challenging for humans and robots. If there were equatorial places where ice could be found at shallow depth, then we would have the best of both environments: warmer conditions for human exploration and still access to ice,” said Lee.

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

Reference: “A Relict Glacier Near Mars’ Equator: Evidence for Recent Glaciation and Volcanism in Eastern Noctis Labyrinthus” by Pascal Lee, Sourabh Shubham and John W. Schutt, 2023, 54th Lunar and Planetary Science Conference.
Abstract: https://www.hou.usra.edu/meetings/lpsc2023/pdf/2998.pdf