"The presence of these features at a high elevation on the mountain indicates that groundwater persisted in this area of Mars later than previous orbital data suggested."
New Clues from Mount Sharp
NASA's Curiosity Mars rover has concluded a six-month investigation of a geological region on Mount Sharp characterized by "boxwork" formations—networks of low, interconnected ridges. The rover's analysis of rock samples and surface features has provided new data on the mineral composition and formation processes of these structures.
Terrain and Geological Features
The boxwork region consists of narrow ridges, 1 to 2 meters (3 to 6 feet) tall, separated by sandy, eroded hollows. From orbit, these crisscrossing patterns resemble a giant spiderweb. The terrain posed operational challenges for the SUV-sized rover, as the ridge tops are often only slightly wider than the rover itself.
Formation Hypothesis
Scientists propose that the formations developed when groundwater moved through large fractures in the bedrock, depositing minerals that hardened the rock along these cracks. Over time, the unreinforced surrounding rock eroded away, leaving the ridge network. Prior to Curiosity's arrival on the scene, only orbital images of these formations were available.
Evidence of Ancient Groundwater
The location of the boxwork on Mount Sharp—a 5-kilometer (3-mile) tall mountain—is significant. Each layer of the mountain formed during a different era of Mars' ancient climate, with higher elevations generally showing more evidence of water drying out, interspersed with periods when rivers and lakes returned. The observation of boxwork at this altitude implies a historically high groundwater table, indicating that water required to sustain life may have been present longer than earlier orbital assessments suggested.
Confirmation of Central Fractures
In 2014, orbital imagery identified dark lines within the spiderweb-like ridges, which scientists hypothesized were central fractures where groundwater permeated and concentrated minerals. Curiosity's close-up examination has confirmed these dark lines are central fractures, supporting the groundwater hypothesis.
Nodule Discovery
The rover also identified small, bumpy structures known as nodules, which are associated with ancient groundwater activity. These nodules were located along the sides of the ridges and within the sandy hollows, rather than near the central fractures. Researchers are investigating why the nodules are positioned in this manner, hypothesizing that the ridges may have been cemented by minerals first, with subsequent groundwater episodes forming nodules around them.
Sample Analysis
A core component of Curiosity's mission is the collection and analysis of rock samples using a drill and onboard instruments. Over the past year, the rover analyzed three samples from the boxwork region: one from a ridge top, one from bedrock in a hollow, and one from a preceding area. X-ray analysis and high-temperature heating identified:
- Clay minerals in the ridge sample.
- Carbonate minerals in the hollow sample.
Subsequently, a fourth sample was collected for a specialized wet chemistry analysis. This method involves heating the powdered rock and introducing chemical reagents to enhance the detection of organic compounds—carbon-based molecules that are fundamental to the chemistry of life.
Future Plans
Curiosity is scheduled to depart the boxwork region in March. The rover is currently situated within a sulfate-rich layer of Mount Sharp, where these minerals formed as Mars' water receded. Over the coming year, the rover will continue to traverse this sulfate-rich layer, collecting additional data to further understand the evolution of the ancient Martian climate billions of years ago.
Mission Background
Curiosity was developed and is managed by NASA’s Jet Propulsion Laboratory (JPL) as part of NASA’s Mars Exploration Program. Images cited in this report were taken by one of Curiosity’s Navigation Cameras on Sol 4928 (June 17, 2026).