For years, researchers have been fascinated by the peculiar, slender pathways meandering through certain sand dunes on Mars. These Martian characteristics are unique and unlike anything found on Earth. Initially, it was believed that these depressions were formed by flowing water, potentially when Mars had a more temperate and humid climate millions of years ago. This notion thrilled scientists as it implied that Mars may have once been capable of supporting life.

Nevertheless, newer satellite images have indicated that these depressions are not merely remnants of the past, but are actively forming and evolving with the seasons, deepening the enigma. Lonneke Roelofs, a geoscientist from Utrecht University in the Netherlands, was determined to unravel this extraterrestrial riddle. Her inquisitiveness drove her to examine surface processes beyond our planet.

“Mars is presently the sole planet where we have detected these types of gullies,” she stated to Mashable, “making them a rather unique and thrilling landform.”

Rather than depending on computer models, Roelofs and a graduate student visited a laboratory at The Open University in the UK to simulate conditions reminiscent of Mars, incorporating low atmospheric pressure and fine sand. Their experiments unexpectedly replicated the gullies.

These Martian formations, referred to as linear dune gullies, frequently run in parallel and terminate with small depressions. Their widths range from approximately three to 30 feet and can extend from 65 to several hundred feet in length, depending on the dune’s size. Despite their designation, many ditches twist rather than form straight paths. With assistance from NASA’s Mars Reconnaissance Orbiter images, researchers have seen these features transforming during the Martian spring.

“The rate of erosion is influenced by how swiftly the dunes migrate,” Roelofs remarked. “Over a decade, we have observed gullies diminish. Yet, some persist for longer.”

Since Mars currently lacks liquid water on its surface, scientists have explored alternative explanations. One hypothesis involves pieces of frozen carbon dioxide, or dry ice.

During the Martian winter, frost and dry ice collect atop desert dunes in the southern hemisphere, occasionally forming a layer exceeding two feet in thickness. As springtime sunlight returns, the ice warms and fractures, with fragments cascading down the slopes.

Some scientists have theorized that the gullies may be the result of avalanches. However, it remained uncertain how a dry ice avalanche under Mars’ thin atmosphere would compare to snow on Earth.

In the lab’s Mars simulation chamber, the team released blocks of dry ice down slopes of varying angles and monitored their movement. The experiment showcased two distinct behaviors. Their results were published in the journal Geophysical Research Letters.

On steep inclines, the dry ice slid, forming thin, shallow grooves. Conversely, on gentler slopes, the base of the ice converted straight into gas, bypassing the liquid stage, and propelled surrounding sand away due to increased pressure. The ice burrowed downward, creating deeper and more convoluted trenches.

A simple block of ice seemed to move as if it were alive, forming ridges, or levees, on either side. Video documentation of the experiments exemplifies this phenomenon. Roelofs compares the behavior to sandworms in “Dune.”

The experiments also indicated that the ditches can only form on dunes composed of very fine, uniformly sized sand grains. Coarser or more irregular materials hinder the burrowing motion, which might clarify why the gullies manifest in specific Martian locales.

Many planetary scientists have presumed that winding channels invariably signify a former presence of liquid water, with streams sculpting the surface. Yet, at least for Mars, this is not necessarily the case.