What appears to be a spider web when viewed through a satellite turns out to be a drive issue when the “threads” are rocks.
Over the past six months, the Curiosity rover of NASA has been trekking across one of the areas of low, overlapping ridges of the lower slope of Mount Sharp within Gale Crater. The structures, which are called boxwork, are approximately 3 to 6 feet (1-2 meters) high, and there are sandy depressions in between, and were initially identified as a dark-colored lattice in an orbital photograph as slightly out of place on a landscape with winds. At a closer approach, the same geometry turns into a navigation riddle: Curiosity will have to strike a balance between traction and wheel slip, as well as turning constraints, when ascending narrow ridges crests and dropping into soft troughs.
“It almost feels like a highway we can drive on. But then we have to go down into the hollows, where you need to be mindful of Curiosity’s wheels slipping or having trouble turning in the sand,” said operations systems engineer Ashley Stroupe in a NASA Jet Propulsion Laboratory statement. “There’s always a solution. It just takes trying different paths.”
Boxwork is created on Earth when the water is transported through a “system of fractures” in rock and deposits mineral coating on the sides of the cracks. In the long term, erosion will remove the less cemented host rock and the mineralised veins will be left behind in the form of ridges. At the same base recipe on Mount Sharp, the boxwork on Gale Crater is the test item against a Martian version: this mountain is 3-mile-tall (5-kilometer-tall), a stack of sedimentary layers formed during several climate periods. The ascending of the rover works as a geological clock, with steepier landscapes in general bearing more intense marks of dry outbursts, in between transient surface water revivals. That gives these ridges more than a picturesque curiosity; they indicate the channels in which underground waters have moved, and in which the mineral growth might have fixed the records of the chemicals in the rock.
One of these hints was in the eye of the sky: dark, thin smears, traversing the lattice. In 2014, it was postulated that these were the centrifugal fractures, in which mineral deposition was concentrated by groundwater. The closer examination of curiosity revealed that the dark lines are cracks and this supports the notion that fluids were taking advantage of cracks and selectively making sections of the bedrock stronger. There were also nodules, which are rough surfaces frequently linked to ancient water on Mars, that were located along the ridge walls and in depressions instead of the fractures as the team has not yet clarified.
The same statement was made by Rice University researcher and mission scientist Tina Seeger when she mentioned that seeing boxwork that high up the mountain meant the groundwater table must have been fairly high. And that is that water required to support life could have been a lot longer than we imagined when we were looking at orbit.
Curiosity does not only apply to the surface textures. The rover has been sampling with its drill and internal instruments the top of the ridges and nearby hollows in order to make measurements of mineral composition. The ridges have been analyzed as containing clay minerals and the hollows containing carbonate minerals, a correlation that assists in limiting the way fluids transferred and where the chemical environment varied in the boxwork terrain.
Minerals that crystallized underground, where it might have been warmer, and salty liquid water flowing through will be found on these ridges, according to a 2024 statement by the Curiosity team member, Rice University planetary scientist Kirsten Siebach. The microbes on early earth would have been able to survive in a similar environment. It is an exciting place to visit because of that.
With Curiosity about to take off, the boxwork is being used as a stop on the larger goal: a sulfur-bearing layer on Mount Sharp associated with a shift in Mars to colder, drier weather. The ongoing traverse over those salts by the rover is intended to read how the availability of water diminished with the passage of time- and whether or not the resistant chemical markings of that change were buried underground, only to be uncovered afterwards, by the action of the winds on the planet.