Giant Spiderweb Formations on Mars Contain Ancient Evidence of the Planet’s Waterlogged Past
The mystery of Mars’ ancient rivers and lakes continues to pose many questions, but answers may come in the form of spiderwebs — not silky webs spun by spiders, but rock formations that look like massive webs from a birds-eye view.
NASA’s Curiosity Mars rover has been valiantly trudging along rugged landscapes for over 13 years, but a recent leg of its journey has yielded some of the most critical updates on Mars’ past yet. For the past few months, Curiosity has been exploring a peculiar region of Mars that’s riddled with geologic formations called “boxwork,” patterns of low ridges interspersed with hollow ridges. This area has shed light on how groundwater flowed throughout ancient Mars, back when microbial life may have lived on the planet.
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The Origins of Martian Spiderwebs
On its recent travels in the boxwork region, Curiosity has encountered low ridges (roughly 3 to 6 feet tall) with sandy hollows in between them. The boxwork formations, when seen from orbit, appear as webs woven on the planet’s surface.
Boxwork features exist in caves and in dry environments on Earth, too, but they’re not quite the same as the Martian formations. For one, they’re much smaller, only a few centimeters tall.
The formations on Mars are more than just perfect Halloween decorations; they serve as geological evidence of a wet Martian environment that dried up billions of years ago. The boxwork, according to a NASA statement, is the work of groundwater that once flowed through large fractures in the bedrock.
As the groundwater flowed, it deposited minerals that helped the ridges of today’s boxwork solidify. The portions that weren’t supplemented with minerals, meanwhile, were hollowed out by wind. Curiosity’s recent exploration of the boxwork region has allowed scientists to finally get a closer look at these remnants of the planet’s past, which may indicate that the groundwater flow persisted longer than expected.
Crossing a Complicated Landscape
To see the boxwork formations up close, NASA scientists had to carefully direct Curiosity across the tops of ridges.
“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 Ashley Stroupe, an operations systems engineer at NASA’s Jet Propulsion Laboratory, in a statement. “There’s always a solution. It just takes trying different paths.”
Curiosity had to scale Mount Sharp, a 3-mile-tall mountain composed of multiple layers that represent the evolution of Mars’ climate history. As Curiosity climbed higher, the layers revealed how Mars dried out over time, though there were occasional signs of the periodic return of rivers and lakes.
“Seeing boxwork this far up the mountain suggests the groundwater table had to be pretty high,” said Tina Seeger, a planetary geologist at Rice University and one of the mission scientists leading the boxwork investigation in the press statement. “And that means the water needed for sustaining life could have lasted much longer than we thought, looking from orbit.”
Curiosity also found other features that hinted at groundwater flow, including dark lines where water may have seeped through cracks in the rock and bumpy textures called nodules along the walls of ridges and hollows.
Drilling for Minerals
Curiosity has collected multiple samples at the boxwork region by drilling into hollows and ridges, and these samples were later analyzed with X-rays and a high-temperature oven. This analysis has revealed clay minerals in ridge samples and carbonate minerals in hollow samples, both of which could help explain how the formations formed.
The rover recently collected another sample, which was processed with chemical reagents to help researchers detect evidence of certain organic compounds essential to life.
Curiosity will leave the boxwork formations in March, but throughout the year, it will continue to explore parts of Mount Sharp enriched in sulfates. These minerals — residue left after Mars dried out — may help scientists piece together the Red Planet’s ancient climate history.
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