NASA’s Curiosity rover is picking its way through a sprawling network of mineral ridges on Mars, a terrain scientists call “boxwork” that preserves a record of ancient groundwater flowing through fractured rock in Gale Crater. The ridges stand roughly 3 to 6 feet tall, separated by sandy hollows, and are studded with pea-sized mineral nodules along central fractures. On Sol 4636, the rover’s MAHLI camera captured a 50-image mosaic of the formations, and the mission team has since drilled into a ridge target called Nevado Sajama to extract powder for onboard analysis. The campaign amounts to a field test of whether these structures mark a late, widespread pulse of groundwater that may have extended habitable conditions well beyond the era of Gale Crater’s ancient lake.
Why the boxwork ridges reshape the timeline for Martian water
The boxwork terrain is not just visually striking. It carries direct implications for how long liquid water persisted beneath the Martian surface. Each ridge likely formed when mineral-laden groundwater seeped through fractures in sedimentary rock, depositing cements that hardened the surrounding material. Wind later stripped away the softer, less-cemented rock between those fractures, leaving the resistant ridges standing in relief. That sequence, described in a recent update from the mission team, means the boxwork records a groundwater episode that postdates the original deposition of the sediments themselves.
The key question is whether the cements inside these ridges differ chemically from minerals found in earlier formations Curiosity has studied, such as Vera Rubin ridge and the clay-rich Glen Torridon unit. If they do, the boxwork could represent a chemically distinct, post-lake groundwater pulse, one whose timing could eventually be tested by comparing the radiometric or cosmic-ray exposure ages of the ridge cements against those of older diagenetic features. That comparison has not yet been made, but the drilling campaign now underway is designed to gather exactly the kind of compositional data needed to begin.
Scientists are particularly interested in whether the fluids that built the boxwork were oxidizing or reducing, acidic or neutral, and whether they carried elements such as sulfur, chlorine, or silica in unusual abundances. Shifts in those parameters over time would point to evolving subsurface environments, with implications for how long potentially habitable niches persisted after surface lakes dried up. In that sense, the boxwork ridges offer a late chapter in the hydrologic story Curiosity has been piecing together since it landed in 2012.
From ridge traverses to the Nevado Sajama drill hole
Curiosity’s encounter with the boxwork terrain unfolded over months of careful driving and imaging. The rover first crossed ridge-and-trough terrain on Sol 4588, when the science team noted open questions about whether the resistant ridges differ in composition from the trough materials between them. That initial traverse revealed a patchwork of raised, resistant strips alternating with softer, sand-filled hollows, a pattern that hinted at fracture-controlled cementation but left the details unresolved.
By Sols 4649 through 4654, the team was operating within pronounced ridge and hollow morphology and planning an approach to a ridge suitable for drilling. The rover’s navigation cameras and Mastcam images showed ridges aligned in multiple directions, creating a lattice-like texture across the landscape. Selecting a drill site required balancing scientific priorities-sampling the heart of a ridge cement-against engineering constraints, such as stable footing and safe arm reach for the drill hardware.
The MAHLI mosaic acquired on Aug. 21, 2025 (Sol 4636) provided the most detailed close-up view yet. It documented pea-sized nodules clustered along central fractures within the ridges, features that suggest localized mineral precipitation rather than uniform cementation. Some nodules appear partially embedded in the ridge matrix, while others protrude slightly, hinting that they may be compositionally distinct and perhaps more resistant to erosion than the surrounding material. The ridges themselves measure approximately 3 to 6 feet (1 to 2 meters) tall, large enough to create a maze-like obstacle course for the car-sized rover.
During Sols 4723 through 4730, Curiosity drilled into the target dubbed Nevado Sajama, positioned atop one of the boxwork ridges. The rover obtained a drilled powder sample from that ridge-top context and began feeding it to its onboard instruments. The sampling strategy-explicitly contrasting ridge material with nearby hollow material-is central to determining whether the cements that built these ridges have a distinct mineral signature from the surrounding rock. If the ridge sample shows enrichment in particular minerals or elements, it would bolster the interpretation that late-stage fluids selectively strengthened the fracture zones.
Curiosity’s Sample Analysis at Mars (SAM) and Chemistry and Mineralogy (CheMin) instruments are expected to play complementary roles. CheMin can reveal which crystalline minerals dominate the ridge cements, while SAM can detect volatile-bearing phases and measure isotopic ratios that speak to the temperature and composition of the fluids. Together, those data sets will allow researchers to test whether the boxwork formed in a single, brief fluid event or through multiple pulses of groundwater over an extended period.
Building on a decade of groundwater clues
This campaign builds on years of earlier work. Curiosity explored the clay-bearing Glen Torridon unit from January 2019 to January 2021, a stretch that revealed heterogeneous alteration by groundwater fluids of variable chemistry, according to a USGS-hosted overview of that campaign. In those rocks, subtle variations in clay types and vein fillings pointed to shifting fluid conditions long after the original lake sediments were laid down.
Separately, a peer-reviewed synthesis published in the Journal of Geophysical Research: Planets established that long-lived diagenesis at Vera Rubin ridge involved hematite, mineral veins, and other signatures consistent with groundwater activity that persisted longer than the surface lake itself. There, Curiosity found evidence that iron-bearing minerals were repeatedly oxidized and reworked, implying that oxidizing fluids circulated through the subsurface over significant spans of time.
Research published in Nature Astronomy used Curiosity’s CheMin X-ray diffraction data on mudstones lower on Mount Sharp to argue that diagenetic processes have overprinted the original lake sediments in multiple stages. Those authors concluded that the subsurface of Gale Crater remained chemically active long after surface conditions became cold and dry, with groundwater reshaping mineral assemblages in ways that could either preserve or erase potential biosignatures.
The boxwork ridges now under study appear to represent an even later phase in this sequence. If the Nevado Sajama sample and future ridge targets confirm distinct mineralogy or fluid signatures, scientists will be able to place the boxwork within a relative timeline: initial lake deposition, early burial and compaction, intermediate diagenesis at Vera Rubin ridge and Glen Torridon, and finally, late-stage fracture-focused cementation that carved the present-day “spiderweb” landscape.
What comes next for Curiosity in the boxwork maze
In the near term, Curiosity’s team plans additional contact science on both ridge tops and adjacent hollows, using the rover’s arm-mounted instruments to map fine-scale variations in texture and chemistry. Short drives between nearby ridges will let scientists test how uniform the boxwork is across Gale Crater’s lower slopes: whether all ridges share a common cement, or whether different patches record distinct fluid events.
Farther ahead, the rover is expected to continue its climb up Mount Sharp, leaving the densest boxwork behind but carrying its geochemical story into higher, younger strata. By comparing the Nevado Sajama results with samples from overlying units, researchers hope to determine whether late-stage groundwater activity was confined to specific layers or pervaded the mountain more broadly.
Whatever the outcome, the boxwork campaign underscores a central lesson of Curiosity’s mission: Mars’ habitability cannot be judged solely by its ancient lakes and rivers. The subsurface, sculpted by groundwater long after surface water vanished, may have hosted the planet’s last refuges for life. With each ridge it drills and each mosaic it returns, Curiosity is tightening the constraints on how long those hidden environments endured-and how complex Mars’ watery past truly was.
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*This article was researched with the help of AI, with human editors creating the final content.
