Nasa’s Curiosity rover has been investigating the spider-web-like rock formations found on Mars – and found mysterious egg-like structures.
Newly issued images show giant zig-zagging ridges, known as ‘boxwork’, spread across the slopes of Mount Sharp inside Gale Crater.
Some of the close-up photographs reveal small, rounded spheroids scattered across the formations, features not previously seen on Mars.
Over the past eight months, Curiosity has been closely examining these interconnected rocky ridges, which stretch across an area up to 12 miles (20km) wide.
Scientists believe the structures formed billions of years ago, when groundwater flowed beneath the Martian surface, depositing minerals that later hardened into ridges as surrounding rock was eroded by wind.
From orbit, the formations resemble enormous spiderwebs etched into the landscape.
Although they were first identified by spacecraft in 2006, their remote location meant they remained largely unexplored until Curiosity arrived.
For about six months, the rover has been driving across the low ridges, which stand roughly three to six feet (one to two metres) tall, with sandy hollows in between.
The patterns suggest groundwater was present in this region later in Mars’ history than scientists had previously thought, raising fresh questions about how long microbial life might have survived on the planet.
To explain the shapes, researchers believe water once flowed through fractures in the bedrock, leaving minerals behind. These minerals strengthened certain areas, forming ridges, while the surrounding rock without this reinforcement was gradually worn away.
Until Curiosity reached the site, scientists were unsure what the formations would look like at ground level or how difficult they would be to traverse.
As the rover climbed higher up Mount Sharp, which rises about 3 miles (5km) above the crater floor, the layers of rock show evidence of Mars’ changing climate. Higher layers suggest increasingly dry conditions, interrupted by occasional wet periods when rivers and lakes may have returned.
Tina Seeger, of Rice University, is one of the scientists leading the investigation.
‘Seeing boxwork this far up the mountain suggests the groundwater table had to be pretty high,’ she said.
‘And that means the water needed for sustaining life could have lasted much longer than we thought looking from orbit.’
Previous orbital images had shown dark lines running through the spiderweb-like patterns. Scientists had suggested these might be fractures where groundwater once flowed.
Curiosity’s close-up investigations have now confirmed that these lines are indeed fractures.
The rover has also identified small, bumpy egg-like features known as nodules, which are considered clear signs of past groundwater activity.
However, scientists were surprised to find that the nodules were located along the sides of ridges and in the hollows, rather than near the central fractures.
‘We can’t quite explain yet why the nodules appear where they do,’ Seeger said. ‘Maybe the ridges were cemented by minerals first, and later episodes of groundwater left nodules around them.’
Curiosity has drilled several rock samples from the region, analysing the powdered material using X-rays and high-temperature ovens inside the rover. The results have revealed clay minerals in the ridges and carbonate minerals in the hollows, offering further clues to how the formations developed.
A more recent sample was analysed using a specialised wet-chemistry technique designed to help detect organic compounds, carbon-based molecules considered important to the origins of life.
The rover is expected to leave the boxwork region in March and continue exploring a wider sulfate-rich layer of Mount Sharp.
Scientists hope the ongoing mission will provide further insight into how Mars’ climate evolved billions of years ago, transforming the planet from one with flowing water into the cold, dry world seen today.
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