Scientists aren’t entirely sure how life began on Earth, but one prevailing theory posits that persistent cycles of wet and dry conditions on land helped assemble the complex chemical building blocks necessary for microbial life. This is why a patchwork of well-preserved ancient mud cracks found by NASA’s Curiosity Mars rover is so exciting to the mission’s team.
A new paper in Nature details how the distinctive hexagonal pattern of these mud cracks offers the first evidence of wet-dry cycles occurring on early Mars.
“These particular mud cracks form when wet-dry conditions occur repeatedly, perhaps seasonally,” said the paper’s lead author, William Rapin of France’s Institut de Recherche en Astrophysique et Planétologie.
The Curiosity rover is gradually ascending the sedimentary layers of Mount Sharp on Mars, which stands 3 miles (5 kilometers) high in Gale Crater.
The rover spotted the mud cracks in 2021 as it explored a rock target nicknamed “Pontours,” found within a transitional zone between a clay-rich layer and one higher up that is enriched with salty minerals called sulfates. While clay minerals usually form in water, sulfates tend to form as water dries up.
The minerals prevalent in each area reflect different eras in Gale Crater’s history. The transitional zone between them represents a period when the lakes and rivers that once filled the crater had begun to recede after long dry spells became prevalent.
As mud dries out, it shrinks and fractures into T-shaped junctions, like what Curiosity discovered previously at “Old Soaker,” a collection of mud cracks lower down on Mount Sharp. Those junctions are evidence that Old Soaker’s mud formed and dried out once, while the recurring exposures to water that created the Pontours mud caused the T-junctions to soften and become Y-shaped, eventually forming a hexagonal pattern.