A Sea of Polygons on Mars
The surface of Mars is home to some of the most breathtaking and awe-inspiring landscapes in the solar system. This is primarily because the Red Planet lacks several resurfacing processes that Earth possesses, including plate tectonics, volcanism, and flowing water. While Mars does have dust storms, these have done little to reshape the planet's surface, which has remained largely undisturbed for billions of years. However, this near-pristine landscape has enabled scientists to look back in time while slowly piecing together what Mars was like long ago.
Now, NASA's Mars Curiosity rover has beamed back images of a landscape featuring polygon-like features. This unique landscape has been observed in other regions of Mars but was a first-time observation for the car-sized rover.
Hypotheses and Ancient Clues
It is hypothesized that these polygonal features form as mud cracks, a process discussed in a 2023 study published in Nature, in which researchers hypothesized that intense wet-dry cycles formed the features from Curiosity rover observations within Gale Crater. That study concluded that the mud cracks could have formed during what's known as the Noachian-Hesperian transition, which occurred about 3.8–3.6 billion years ago and which researchers have hypothesized is when Mars could have exhibited an Earth-like climate.
However, researchers studying these new polygonal features suggest more work is needed to understand their formation processes. The features measure about 4–8 centimeters (1.5–3 inches) across.
"We've seen a lot of fascinating landscapes through Curiosity's eyes, but this sea of polygons took our breath away," said Dr. Ashwin Vasavada, a Curiosity rover mission scientist at NASA's Jet Propulsion Laboratory. "We measured their shapes and chemistry carefully and are hopeful there are clues in the data as to how these features formed."
Comparing Ground-Level and Orbital Views
As noted, polygonal features have been observed across Mars. While these latest polygons are hypothesized to have formed as mud cracks, polygons in other regions of Mars are hypothesized to have formed from freeze-thaw cycles or from tectonic or volcanic stress.
Gale Crater is the only region observed at ground level by a rover that has shown mud cracks. Other polygonal surface features have been observed by NASA's High Resolution Imaging Science Experiment (HiRISE) orbiter, which has orbited Mars since 2006. The primary difference between ground-level and orbiter observations is the size of the polygons: ground-level polygons are about the size of those observed by Curiosity, while orbiter polygons range from 15 to more than 350 meters (50 to more than 1,000 feet) in diameter.
Examples of regions with crater floor polygons include Hellas Planitia, Noachis Terra, and Margaritifer Terra. Hellas Planitia is the largest impact basin on Mars, measuring about 2,300 kilometers (1,400 miles) in diameter and just over 7,000 meters (23,000 feet) deep beneath the Mars datum.
A Window into Mars's Past
Today, Mars's surface displays processes from the Pre-Noachian, Noachian, and possibly Hesperian periods, which are estimated to have collectively spanned 4.5–3.0 billion years ago; the current period is the Amazonian period. The near-pristine state of the Martian surface allows scientists to study these ancient features, offering a glimpse into the planet's climate and conditions billions of years ago.