I remember the first time I saw a mudcrack in the Arizona desert—a dried-up pond bed, split into a jigsaw of five- and six-sided plates. It felt like nature’s way of doodling. But that memory came rushing back as I read the latest update from Mars, where NASA’s Curiosity rover is now trundling through a landscape that looks like the same thing, only writ large and ancient. This isn’t a dry lake bed from last summer. This might be a billion-year-old whisper of water.
Curiosity’s latest traverse, covering Sols 4934 to 4940—that’s Martian days, for the uninitiated—has brought the rover into a unit that, from orbit, appears light-toned and fractured. The team calls it “the land of the polygons,” and for good reason. The ground is crisscrossed with ridges forming geometric shapes, some as big as cars. It’s a geological puzzle, and William Farrand, a senior research scientist at the Space Science Institute, is one of the people trying to piece it together.
What Are These Polygons, Anyway?
The polygons Curiosity is driving over aren’t just pretty patterns. They’re clues. On Earth, similar features form when wet sediment dries and contracts, or when freeze-thaw cycles crack the ground. On Mars, the leading hypothesis points to ancient lakebeds or mudflats that dried out billions of years ago. The light tone from orbit? That could be a sign of salts or fine-grained sediments that reflect sunlight differently than the darker, dustier surroundings.
“We’re seeing these polygonal fracture networks that are very similar to what we see in terrestrial playas—dry lakebeds,” Farrand told me. “The challenge is that Mars doesn’t give up its secrets easily. We have to look at the chemistry, the mineralogy, and the morphology all together.” And that’s exactly what the rover is doing. Over the two planning cycles this week—Monday and Friday—Curiosity has been using its Mastcam and ChemCam to zap and photograph the polygons, building a dataset that could confirm whether this region was once a shallow lake.
A Week of Two Plans
The planning for Sols 4934–4940 wasn’t straightforward. The Monday plan focused on a particularly interesting polygonal block that the team nicknamed “Garnet Ridge.” The rover parked, extended its arm, and used the Mars Hand Lens Imager (MAHLI) to get microscopic images of the surface. Then ChemCam fired its laser—100 shots per target—to vaporize tiny bits of rock and analyze the vapor’s composition. The results showed elevated levels of calcium sulfate, a mineral that often precipitates from water. That’s not proof of a lake, but it’s one more piece of the puzzle.
By Friday, the team had shifted focus to a lighter-toned patch about 10 meters away. “We wanted to see if the color difference from orbit was just dust or an actual compositional change,” Farrand said. “So we did a ‘touch-and-go’—touch the surface with the arm, then drive forward.” The drive took Curiosity about 25 meters, a modest hop but a significant one, given the rough terrain. The rover’s wheels have taken a beating over the years, so the team is careful about sharp rocks. The polygons, thankfully, are mostly flat.
What This Means for Mars’s Wet Past
This isn’t the first time Curiosity has found polygons. The rover saw similar features back in 2015 in the “Pahrump Hills” area. But this new site is different. It’s closer to the sulfate-rich unit that Curiosity has been climbing toward for months—a layer that orbital data suggests formed in a much saltier, more acidic environment. The polygons here might represent a transition: a last gasp of neutral-pH water before Mars dried into the acidic, arid world we see today.
Context matters. Curiosity landed in Gale Crater in 2012, and since then, it’s been slowly climbing Mount Sharp, the 5-kilometer-high mound at the crater’s center. Each layer of rock tells a chapter of Mars’s climate story. The polygonal unit sits at an elevation of about 4,500 meters above the crater floor—a sweet spot where the rock record shifts from clay-rich (indicating wet conditions) to sulfate-rich (indicating drier, saltier conditions). “The polygons could be the smoking gun for that transition,” Farrand said. “If we can show they formed in a wet-dry cycle, it supports the idea that Mars had episodic, not just constant, water.”
And episodic water is exactly what astrobiologists are after. Why? Because wet-dry cycles are thought to be a key ingredient for the chemical reactions that might have led to life. Mega-droughts on Earth are reshaping our own water cycles—but on Mars, those ancient cycles may have been the crucible for prebiotic chemistry. It’s a humbling parallel.
The Road Ahead
Curiosity won’t linger in polygon land forever. The plan for the next few weeks is to continue climbing, targeting a ridge called “Junda” that’s visible from orbit. But before moving on, the team wants to drill one of the polygon blocks—if the rock is soft enough. Drilling on Mars is always a gamble; the rock could be too hard, or the drill could jam, as it did back in 2016. But if it works, the powdered sample could be fed into the rover’s internal labs, SAM and CheMin, for definitive mineral analysis.
For now, the rover is healthy, the science is rolling, and the polygons are yielding their secrets one laser shot at a time. Farrand summed it up neatly: “We’re in a beautiful, weird place. And we’re reading the story of Mars in the cracks.” It’s a story that’s still being written—line by line, sol by sol, polygon by polygon.
Frequently Asked Questions
Q: What are the polygons on Mars made of?
A: The polygons are likely fractured sedimentary rock, possibly mudstone or siltstone, that formed when wet sediments dried and cracked. The light tone suggests they may contain salts or fine-grained minerals. Curiosity’s ChemCam has already detected calcium sulfate, which is common in evaporative environments.
Q: How does this discovery relate to the search for life on Mars?
A: Wet-dry cycles, which create polygonal cracks, are thought to concentrate organic molecules and drive chemical reactions that could lead to the building blocks of life. If Curiosity confirms that these polygons formed in such cycles, it strengthens the case that Gale Crater once had habitable conditions.
Q: Why is the rover climbing Mount Sharp instead of driving across the crater floor?
A: Mount Sharp’s layers are like a stack of history books. Each elevation exposes rocks from a different time period, allowing scientists to study how Mars’s climate changed over billions of years. The polygonal unit sits at a key transition between wetter and drier periods.
