Skylights in Hebrus Valles Suggest Karst Caves on Mars — Potential Refuges for Past Life and Astronauts

Skylights in Hebrus Valles Point to Water‑Carved Caves

Mars is an extremely hostile environment: temperatures can plunge below −100 °F, the surface is bombarded by intense ultraviolet radiation, and powerful dust devils can whip winds approaching 99 mph. Given those extremes, any organisms that once lived on Mars—or that might still survive there—would have been far better off sheltered underground in caves.

Now, a team of researchers from China and Italy report the possible discovery of a new class of Martian cave formed by liquid water dissolving soluble rocks. Unlike most known Martian caves, which owe their origins to volcanic or tectonic activity, these proposed features are karstic—created by chemical erosion—making them especially intriguing as targets in the search for past habitability.

What are karstic caves?

On Earth, karst systems develop where slightly acidic groundwater dissolves soluble rock layers such as limestone or gypsum, widening fractures over time until they form caves. The researchers propose that ancient Martian water flows could have similarly dissolved carbonate‑ and sulfate‑rich strata in the crust, leaving behind voids and surface openings known as skylights.

Evidence from Hebrus Valles

The team identified several skylight candidates in the Hebrus Valles region, an area marked by troughs and channels consistent with past flooding. Using high‑resolution data and imagery from NASA missions including Mars Global Surveyor and Mars Odyssey, they closely examined eight pits. These features differ from impact craters: they are deep, largely circular depressions and are surrounded by rock units enriched in carbonates and sulfates—minerals that readily dissolve in liquid water.

“These skylights represent promising subsurface refugia,” the authors wrote, noting that such pits could preserve traces of past water activity and potentially remnants of past life.

Why this matters

If confirmed, karstic caves would be important for both astrobiology and exploration. Subsurface voids can protect organic molecules and microbial fossils from harsh surface radiation and temperature swings, increasing the chance that any biosignatures would survive. In addition, skylights and caves could offer sheltered sites for future robotic missions and, eventually, human explorers seeking protection from radiation and extreme weather.

The researchers published their findings recently in The Astrophysical Journal Letters. While the evidence is compelling, further observations—ideally higher‑resolution imaging and, eventually, in situ exploration—are required to confirm the karstic origin of these pits and to assess their astrobiological potential.

Note: The interpretation is cautious and does not claim direct evidence of life—only that these features, if karstic, are promising locations to search for preserved signs of past water activity and potential biosignatures.