Somewhere near the Martian equator, a gash in the planet’s surface runs so wide it would stretch from New York to Los Angeles. Valles Marineris is not just a canyon; it is a cross-section through billions of years of Martian history, its walls stacked with mineral layers the way tree rings record seasons. And those layers are finally being read in detail.
A peer-reviewed study published in Icarus has mapped hydrated sulfates and chemically altered minerals along the steep flanks of Ius Chasma, one of the canyon system’s deepest segments. The sulfate signatures point to something remarkable: liquid water, likely acidic brine, pooling inside the canyon long enough to soak into rock and leave a permanent chemical imprint. This was not a single flash flood. The mineral patterns require sustained, repeated wetting over geological time.
Meanwhile, the James Webb Space Telescope has turned its infrared instruments toward Mars on multiple occasions. JWST’s first Mars observations, captured using NIRSpec and NIRCam, produced atmospheric and surface composition data released by NASA in 2022 and analyzed in a 2023 study in Nature. While those early JWST datasets covered broad surface regions rather than targeting specific canyon-wall outcrops, the telescope’s spectral sensitivity opens a new window for future mineral mapping at sites like Ius Chasma, complementing the orbital instruments that have already rewritten our understanding of what lies inside those walls.
A layer cake of fire and water
The research team behind the Icarus study used compositional maps from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) aboard NASA’s Mars Reconnaissance Orbiter, then cross-referenced them with stereo topography from the European Space Agency’s HRSC camera and high-resolution HiRISE imagery. The sulfate zones they identified are not scattered randomly. They follow specific elevation bands along the canyon walls, consistent with brine overflow and acid alteration of exposed rock at distinct water levels.
But the sulfates are only half the story. Interbedded with those water-altered layers are dark basaltic units, the frozen remnants of volcanic lava flows that built Mars’s crust over hundreds of millions of years. A USGS analysis of dark materials within Valles Marineris treats the canyon as a natural drill hole into kilometer-deep crustal rock, exposing volcanic and magmatic layers that would otherwise remain buried. JPL imaging of the canyon’s wall stratigraphy describes these equatorial layers as a direct record of crust formation, dominated by basaltic and pyroxene-rich compositions typical of Mars’s upper crust.
The result is a vertical timeline where volcanic construction and aqueous chemistry alternate. One layer records a lava flow hardening into basalt. The next records water seeping through fractures, dissolving minerals, and depositing sulfates as it evaporated. Then another lava flow sealed the sequence, preserving it for billions of years until tectonic forces ripped the canyon open and exposed the entire stack.
Bright outcrops high in the walls
Some of the most striking evidence sits not on the canyon floor but high on the walls themselves. NASA’s Photojournal documents bright, layered rock outcrops first captured by Mars Global Surveyor’s Mars Orbiter Camera. Their position, hundreds of meters above the canyon bottom, and their apparent age suggest they formed during early episodes of crustal construction, long before the canyon reached its current depth.
Deeper inside the canyon, interior layered deposits (ILDs) present their own puzzle. These thick sedimentary stacks sit on the canyon floor, and their origin remains actively debated. NASA describes competing explanations: wind-blown sediments accumulated over eons, volcanic ash and lava, landslide debris, or lakebed sediments deposited when the canyons held standing water. The ILDs may record a different chapter of the canyon’s history than the wall outcrops, potentially a later period when water filled the deepest parts of the system.
On the canyon floor, orbital views reveal stacked sedimentary sequences with laterally continuous beds, erosional benches, and talus slopes. Whatever deposited them, whether water, wind, or volcanic fallout, operated over extended periods. This was not a single catastrophic event but a drawn-out geological process, or more likely, many processes layered on top of one another.
The volcanic neighborhood
Ius Chasma does not exist in isolation. West of Valles Marineris, the fractured terrain of Noctis Labyrinthus contains multiple depressions where water-bearing minerals have been detected from orbit. A separate Icarus study linked a hydrated, light-toned alteration unit in one Noctis chasma directly to local volcanic activity, providing a concrete mechanism: magmatic heat drove groundwater through rock, altering minerals and leaving hydrated signatures behind.
Farther west, the Tharsis volcanic province, home to Olympus Mons and three other massive shield volcanoes, looms over the region. Mars Express OMEGA and HRSC data show relatively recent volcanic plains in Tharsis, indicating that heat sources persisted in this equatorial belt long enough to sustain both volcanic resurfacing and aqueous chemistry. The implication is that heat and water coexisted across a broad swath of equatorial Mars, not just within a single canyon. Wherever tectonics and volcanism cracked the surface, subsurface water found pathways upward.
What the data cannot yet tell us
For all the detail in the orbital record, significant gaps remain. No rover or lander has visited the equatorial wall exposures of Valles Marineris. The canyon walls are too steep and the terrain too hazardous for any landing technology currently in operation. Mars rovers have sampled sulfate-bearing rocks elsewhere, notably Curiosity in Gale Crater, but the specific bright outcrops high in the Ius Chasma walls remain accessible only through remote sensing. Until a surface mission reaches these deposits, the mineralogical interpretations carry an inherent margin of uncertainty tied to spectral resolution, atmospheric interference, and the difficulty of unmixing complex rock assemblages from hundreds of kilometers above.
Timing is another open question. The relative ages of volcanic flows, tectonic faulting, and aqueous alteration can be estimated from crater counts and cross-cutting relationships, but the precision is coarse, often spanning hundreds of millions of years. If some sulfate-rich layers formed much later than the main phase of canyon opening, they might record localized groundwater upwelling rather than an early, globally significant wet period. Current data cannot fully separate these scenarios.
Quantitative thickness and volume estimates for the layered deposits draw on older USGS topographic analyses that have not been updated with newer spectral datasets. The gap matters because vertical zoning of sulfate minerals, if it follows a systematic brine-evaporation sequence rather than uniform volcanic ash alteration, would distinguish repeated localized water-filled basins from a single regional lake. That distinction has not been resolved by any published dataset as of mid-2026.
Why it matters beyond geology
The question of whether Valles Marineris hosted long-lived water is not purely academic. Sustained liquid water, especially water warmed by volcanic heat, creates the kind of environment where microbial life could theoretically have gained a foothold. The sulfate deposits in Ius Chasma are chemically similar to minerals found in terrestrial environments that support extremophile organisms, such as acid mine drainage systems and volcanic hot springs. That parallel does not prove anything lived in the Martian canyon, but it places these deposits squarely on the short list of targets for future astrobiology missions.
The emerging picture is compelling but incomplete. Valles Marineris and Ius Chasma almost certainly hosted long-lived interactions between volcanic heat and liquid water. The mineral evidence, drawn from multiple instruments across multiple missions, converges on that conclusion. But the exact form of those environments, whether deep lakes, shallow brine pools, or circulating groundwater systems, remains an active area of research. Each new dataset, whether from JWST’s infrared instruments, future orbital missions, or an eventual surface explorer, will add another line to a story that has been locked inside those canyon walls for more than three billion years.
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*This article was researched with the help of AI, with human editors creating the final content.
