For as long as humans have stared at the soft red glow of Mars, we’ve wondered whether something once stirred beneath its rusty soil. The surface, with its dust storms sharp as sandpaper and temperatures that swing wildly between freezing and bitterly freezing, seems like a poor cradle for life. But the surface was never the only place to look. If Mars ever offered refuge to anything living, it may have done so in places the Sun barely reaches: caves, carved into the crust, waiting in silence.
Now, a new discovery is shifting the search underground with more focus than ever before. Eight mysterious holes—“skylights,” as scientists call them—may be far more than simple pits. They might be entrances to an entirely new class of Martian caves, created not by fire or volcanic fury, but by the patient, ancient work of water.
A World Beneath the Dust
The story begins with Chenyu Ding of Shenzhen University in China and a team of colleagues who turned their attention to a northwestern region of Mars called the Hebrus Valles. This rugged landscape, shaped by time and turbulence, had already been mapped by past Mars missions. In the data, eight deep, circular depressions stood out. They did not have the typical raised rims or ejected debris that would suggest meteor impacts. These were something else—something hollow.
In their paper published in The Astrophysical Journal Letters, the researchers announced that these pits are likely collapse entrances to caves shaped not by lava, but by dissolving rock. Most caves on Mars identified to date have been volcanic lava tubes, frozen traces of ancient flows. But Ding and his team argue that these are different: they are karstic caves, formed when water eats away at soluble rock.
“These skylights are interpreted as the first known potential karstic caves on Mars, representing collapse entrances formed through the dissolution of water-soluble lithologies—defining a new cave-forming class distinct from all previously reported volcanic and tectonic skylights,” wrote the researchers.
If true, it means Mars once hosted water capable of dissolving carbonate- and sulfate-rich rocks, carving out cracks and chambers over long periods—much like how limestone caves grow on Earth.
Ghosts of Water Long Gone
To uncover this possibility, the team sifted through data from the Thermal Emission Spectrometer (TES) aboard NASA’s Mars Global Surveyor. TES is designed to read the mineral fingerprints of Martian terrain, and around these eight pits, it detected rocks rich in carbonates and sulfates. These minerals dissolve easily in water, making them perfect candidates for karstic cave formation.
The researchers then paired these findings with high-resolution imagery. They built 3D models of the pits, revealing structural shapes that looked far more like collapse features created by underground cavities than anything volcanic or tectonic. The pits’ clean, circular forms hinted at chambers beneath them—chambers that may have once grown through the steady drip and flow of ancient water.
On Mars, where any trace of long-standing liquid water is precious, this alone would be remarkable. But these caves could hold something even more compelling.
A Natural Hideaway for Possible Life
If life ever found a foothold on Mars, it would have needed protection. The surface, blasted by radiation and stripped of its once-thicker atmosphere, is hostile to even the hardiest microbes. Caves, however, offer shelter. They shield against radiation, buffer extreme temperatures, and provide stable environments long after the surface becomes unlivable.
That’s why the idea of karstic caves—water-made caves—is electrifying. They don’t simply suggest shelter. They suggest a history of water flow, perhaps gentle and persistent enough to shape rock into caverns. If these pits do open into such spaces, they could represent some of the most promising places yet to search for life’s fingerprints.
The eight skylights in Hebrus Valles, then, become more than holes in the ground. They become portals into Mars’ hidden past.
A New Priority for Explorers
The search for life on Mars has always felt overwhelming, like trying to spot a single glimmer in a vast desert of dust. But Ding and his colleagues argue that discoveries like these can bring order to the search, pointing missions toward the places most likely to hold answers.
They believe the eight possible karstic caves should be high-priority targets for upcoming missions, whether robotic or human. Even if no life waits in the shadows below, the caves could still hold enormous value. Their natural sheltering structure might one day protect astronauts from radiation and storms, turning them into ready-made havens for explorers stepping onto Martian soil.
With each new finding, Mars becomes less of a barren question mark and more of a layered history book—written in minerals, carved in stone, and waiting patiently beneath the dust.
Why This Discovery Matters
These possible karstic caves represent more than geological curiosity. They offer the strongest evidence yet that water once seeped through Martian rock long enough to sculpt underground voids. That alone deepens our understanding of Mars’ past environment and the role water played in shaping it.
But even more importantly, the caves give scientists a concentrated set of targets in the quest for life. Instead of scanning endless plains and craters, we now have eight specific points where the right conditions for life might once have existed—and perhaps still do in protected pockets.
In a world where most of Mars remains a mystery, these hidden caverns could become the key to unlocking answers about habitability, exploration, and the planet’s deep-time story. They remind us that Mars is not just a dusty sphere orbiting quietly in the cold, but a world with secrets tucked into its shadows, waiting for someone brave enough to look inside.
More information: Ravi Sharma et al, Water-driven Accessible Potential Karstic Caves in Hebrus Valles, Mars: Implications for Subsurface Habitability, The Astrophysical Journal Letters (2025). DOI: 10.3847/2041-8213/ae0f1c
