For the past six months, NASA's Curiosity rover has been delving into an intriguing Martian region characterized by geological formations known as boxwork. These structures, which rise between 3 to 6 feet (1 to 2 meters) and are separated by sandy depressions, extend for miles across the Martian landscape. The presence of these crisscrossing ridges suggests that groundwater may have flowed through this area later than scientists previously thought, prompting new inquiries into how long microscopic life could have thrived on Mars billions of years ago, prior to the planet's transformation into the cold desert we observe today.
From a distance, the boxwork formations resemble enormous spiderwebs scattered across the terrain. Researchers theorize that these shapes emerged as groundwater infiltrated fractures in the bedrock, depositing minerals that solidified over time into ridges. The surrounding rock, lacking this mineral reinforcement, eroded away, revealing the intricate web-like patterns we see today.
Before Curiosity's arrival, the only way scientists could study these formations was through orbital imagery, leaving many questions regarding their true structure unanswered.
Investigating Martian Boxwork Up Close
While boxwork formations also exist on Earth, they are typically much smaller and found in caves or arid environments. The Martian versions are significantly larger, prompting the Curiosity team to conduct direct investigations and gather detailed measurements.
However, navigating this rugged terrain has proven challenging. Engineers must carefully maneuver Curiosity, an SUV-sized rover weighing nearly 2,000 pounds (899 kilograms), along ridge tops that are often only slightly wider than the rover itself.
"It feels like a highway we can drive on, but we also have to navigate down into the hollows, being cautious of Curiosity's wheels slipping in the sand," explained Ashley Stroupe, operations systems engineer at NASA's Jet Propulsion Laboratory. "There's always a solution; it just requires exploring different paths."
Scientists are keen to understand how such an extensive network of ridges formed on Mount Sharp, a towering 3-mile-high (5-kilometer-high) mountain that Curiosity is currently exploring. Each layer of the mountain reveals a different chapter in Mars' climatic history, showing signs of water's gradual disappearance over time, interspersed with wetter periods that allowed rivers and lakes to re-emerge.
"Finding boxwork this high up the mountain indicates that the groundwater table must have been relatively high," noted Tina Seeger from Rice University, one of the mission scientists leading the boxwork investigation. "This suggests that the water necessary to support life could have persisted longer than previously thought based on orbital observations."
Evidence of Ancient Groundwater
Earlier satellite imagery also highlighted dark lines running through the spiderweb-like ridges. Researchers proposed in 2014 that these streaks might indicate central fractures where groundwater seeped through rock cracks, concentrating minerals.
Curiosity's close-up analysis has confirmed these dark lines are indeed fractures, reinforcing the idea that groundwater played a crucial role in shaping these ridges.
The rover has also discovered small, bumpy structures known as nodules, which are often associated with ancient groundwater activity. Surprisingly, these nodules are not found near the central fractures but rather along the ridge sides and within the sandy depressions.
"We are still trying to understand why the nodules are located where they are," Seeger said. "Perhaps the ridges were first cemented by minerals, with subsequent groundwater episodes creating the nodules around them."
Curiosity as a Mobile Chemistry Lab
A significant aspect of Curiosity's mission involves drilling rock samples. The rover grinds rock into powder, which is then analyzed by sophisticated onboard instruments.
Last year, scientists examined three samples from the boxwork area, discovering clay minerals within the ridges and carbonate minerals in the hollows. These findings provide valuable insights into the processes that formed this unique terrain.
Recently, Curiosity collected a fourth sample for specialized analysis. After heating the powdered rock, chemical reagents were added to conduct wet chemistry, revealing carbon-based molecules that are essential for life.
Continuing the Search for Mars' Climate History
Curiosity is set to move on from the boxwork region in March, as it continues its journey through a sulfate-rich layer of Mount Sharp, gathering new evidence about the ancient climate of Mars.
This ongoing exploration not only enhances our understanding of Mars' geological history but also raises intriguing possibilities regarding the planet's potential to have supported life.