Evidence of Mars' wet past found preserved in ancient mud

The rover has documented patches of well-preserved ancient mud cracks, indicating that Mars had periodic wet-dry cycles 3.6 billion years ago.
Mrigakshi Dixit
A location nicknamed “Pontours” on Mars where preserved, ancient mud cracks were formed during long cycles of wet and dry conditions
A location nicknamed “Pontours” on Mars where preserved, ancient mud cracks were formed during long cycles of wet and dry conditions

NASA/JPL-Caltech/MSSS/IRAP 

NASA's Curiosity rover has discovered new compelling evidence of Mars' soggy past. 

The rover has documented patches of well-preserved ancient mud cracks, indicating that Mars had periodic wet-dry cycles 3.6 billion years ago. This discovery adds to the evidence that the red planet was once likely conducive to life. 

One theory for how life began on Earth postulates that repeated cycles of wet and dry land conditions supplied the ideal mix of conditions for the formation of the complex chemical building blocks necessary for the genesis of microbial life. This hypothesis might also apply to Mars. 

“This is the first tangible evidence we’ve seen that the ancient climate of Mars had such regular, Earth-like wet-dry cycles. But even more important is that wet-dry cycles are helpful – maybe even required – for the molecular evolution that could lead to life,” said William Rapin, the paper’s lead author, in an official release.

The unique polygonal cracks 

In 2021, Curiosity passed over a Martian landscape carved with unique polygonal ridges near the Gale Crater. These patterns have never been observed before on the Martian surface. 

The ground-based mission controllers instructed the rover to drill into a mud crack sample from a rock target known as "Pontours."

The data beamed back revealed the red planet's buried ancient past. The drill samples uncovered a transitional zone between two soil layers under Mars's surface. 

One layer was rich in clay, while the one above it was abundant in salty minerals known as sulfates. Because clay minerals occur in water and sulfates create when water dries up, the existence of these two is strong evidence of wet-dry cycles. 

“The minerals prevalent in each area reflect different eras in Gale Crater’s history. The transitional zone between them offers a record of a period when long dry spells became prevalent and the lakes and rivers that once filled the crater began to recede,” explained NASA. 

Evidence of Mars' wet past found preserved in ancient mud
Close-up of the panorama taken by Curiosity’s Mastcam at “Pontours” reveals hexagonal patterns – outlined in red in the same image, right – that suggest these mud cracks formed after many wet-dry cycles occurring over years.

How were the shapes carved out? 

Mud shrinks and fractures into T-shaped junctions when it dries. NASA adds that the Pontours mud was formed through repeated exposure to water, as the T-shaped joints weakened and turned Y-shaped, eventually leaving behind this seen hexagonal pattern.

The hexagonal cracks in the transitional zone continued to develop even after new sediment was deposited, showing that the wet-dry conditions persisted for a long time.

These hexagonal cracks have remained safe from erosion due to the presence of a tough crust of sulfates at the borders, thereby preserving them for billions of years.

The results have been reported in the journal Nature. 

Study abstract:

The presence of perennially wet surface environments on early Mars is well documented, but little is known about short-term episodicity in the early hydroclimate. Post-depositional processes driven by such short-term fluctuations may produce distinct structures, yet these are rarely preserved in the sedimentary record. Incomplete geological constraints have led global models of the early Mars water cycle and climate to produce diverging results. Here we report observations by the Curiosity rover at Gale Crater indicating that high-frequency wet–dry cycling occurred in early Martian surface environments. We observe exhumed centimetric polygonal ridges with sulfate enrichments, joined at Y-junctions, that record cracks formed in fresh mud owing to repeated wet–dry cycles of regular intensity. Instead of sporadic hydrological activity induced by impacts or volcanoes, our findings point to a sustained, cyclic, possibly seasonal, climate on early Mars. Furthermore, as wet–dry cycling can promote prebiotic polymerization, the Gale evaporitic basin may have been particularly conducive to these processes. The observed polygonal patterns are physically and temporally associated with the transition from smectite clays to sulfate-bearing strata, a globally distributed mineral transition. This indicates that the Noachian–Hesperian transition (3.8–3.6 billion years ago) may have sustained an Earth-like climate regime and surface environments favourable to prebiotic evolution.

Add Interesting Engineering to your Google News feed.
Add Interesting Engineering to your Google News feed.
message circleSHOW COMMENT (1)chevron
Job Board