Ancient dunes on Mars reveal long-lasting underground water

Ancient sand dunes in Gale Crater hold new clues about how long water lingered beneath the surface of Mars.

A team in Abu Dhabi found evidence that small amounts of groundwater once moved through these dunes, leaving behind minerals that Curiosity later detected.

By comparing rover images with naturally cemented dunes in the United Arab Emirates, the researchers showed that Mars stayed wetter – at least underground – long after its lakes vanished.

The study was led by Dimitra Atri, head of the Mars Research Group at New York University Abu Dhabi’s Center for Astrophysics and Space Science (NYUAD).

Signals locked in sandstone

Curiosity imaged ancient dunes that later hardened into sandstone, a process called lithification, the hardening of loose sediment into rock.

The researchers found that fluids rose from below, seeped into these wind-built layers, and left mineral clues behind. These clues include gypsum and other salts that form when water moves through pores and fractures.

The deposits occur within the Stimson Formation at the edge of the Greenheugh Pediment, a site that records some of the Gale Crater’s most recent watery moments.

“Our findings show that Mars didn’t simply go from wet to dry,” said Atri. “Even after its lakes and rivers disappeared, small amounts of water continued to move underground, creating protected environments that could have supported microscopic life.”

Mars’ dunes transformed by water

On Earth, desert dunes can become rock when minerals precipitate between grains, a process called cementation, or mineral growth that binds sand into solid stone.

Evidence from Mars suggests a similar path, with calcium sulfate cements turning loose sand into durable layers.

Why gypsum matters comes down to preservation. Laboratory and field studies in Mars-like deserts show that gypsum can trap organic molecules inside crystals, shielding them from harsh radiation.

That protective effect makes these dunes more than geologic oddities. They are vaults that could keep fragile organic signals intact for long periods under the surface.

The study also points to water moving along a boundary known as an unconformity. This contact can focus flow and create a narrow, stable zone where microbes might have endured.

Gale Crater’s new water clues

Gale Crater has already delivered on the search for ancient habitability. Curiosity has found organic molecules of increasing complexity in mudstones, including the largest compounds detected so far on Mars.

Those organics came from lakebed rocks, yet the new work extends the story to wind-formed dunes on Mars that were later altered by water. It widens the set of places where traces of past life could hide.

Gale’s geology helps explain why. The Stimson sandstones overlie older lake deposits and were later cut by fractures that acted like tiny plumbing, moving fluids upward through permeable layers.

Detailed mapping of Curiosity’s path through Glen Torridon and toward Greenheugh documents shifts from clay-rich mudstones to cemented sandstones.

A USGS report outlines how these units record changing water availability as the climate dried.

Where else water maybe hiding

If dunes turned to stone with the help of late-stage water, then hardened dune fields across Mars deserve closer attention. Their mineral cements may have captured and protected carbon-bearing clues when the surface grew hostile.

Water moving from below would have carried dissolved ions and heat from deeper layers. A shallow aquifer, a rock unit that stores and transmits water, could have periodically recharged these zones even as the atmosphere thinned.

Modeling suggests that water-rock reactions beneath the Greenheugh surface were plausible and could alter chemistry in ways that Curiosity can recognize.

NASA’s NTRS modeling study explores how fluids interacting with basaltic sands would leave sulfate-rich cements and halos.

The preservation angle matters for field planning. Teams can now target specific textures, such as cross bedded sandstones with mineral veins, where fluids concentrated rather than spread out.

This approach complements ongoing searches in lake deposits and deltaic rocks elsewhere on Mars. It also aligns with the broader idea that the best biosignature – a measurable sign of past or present life – is one that was quickly entombed and shielded from radiation and oxidants.

What it means for future missions

The next step is to probe below the surface, where radiation damage drops quickly within a few feet. Drilling a few inches to a few feet could reach cements and mineral veins that never saw open air.

Curiosity has drilled dozens of holes but cannot reach deeper strata where protected material likely resides. With this new map of promising targets, planners can prioritize dune cements and fracture networks when selecting sampling sites.

Sample-return decisions could benefit as well. Rock cores that blend sandstone fabrics with gypsum or other sulfates would carry an extra preservation bonus if cached and returned to Earth.

Meanwhile, Earth analogs remain vital. UAE dune fields that underwent natural cementation provide testbeds to refine protocols and avoid contamination when handling delicate organic signals.

Finally, the picture of Mars that emerges is not a binary switch from oceans to desert. It is a slower fade with lingering pockets where small, shielded ecosystems may have had just enough water and chemistry to hang on.

The study is published in the Journal of Geophysical Research: Planets.

Image Credit: NASA/JPL-Caltech/University of Arizona

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