SCARS on the red planet’s surface have baffled scientists for decades – but an explanation may lie in their recreation of Mars in a barrel.
The spider-like geologic formations have been known to scientists since Mars orbiters returned images in 2003.
However, the spindly structures appear only on the planet’s southern hemisphere.
Dubbed araneiform terrain, they can stretch more than a half mile from end to end, with hundreds of branched “legs.”
The leading theory says the structures were created by carbon dioxide ice, a substance that couldn’t be found on Earth – until now.
A team of Nasa scientists recreated Mars-like conditions on Earth to simulate the process. Their findings were published yesterday in The Planetary Science Journal.
The study supports processes detailed by the Kieffer model, a widely accepted explanation for seasonal changes on the Mars surface.
According to the theory, sunlight heats the Martian soil when it shines through slabs of carbon dioxide ice that build up on the Martian surface each winter.
The soil absorbs the heat and causes nearby ice to turn directly into carbon dioxide gas without becoming liquid first – a process known as sublimation.
As pressure builds, the Martian ice splinters, allowing the gas to escape. It travels upwards, carrying a stream of dark dust and sand that lands on the surface of the ice.
When seasons change and the remaining ice turns to gas, the spiderlike formations remain.
This is, of course, according to theory – leaving Nasa scientists with the momentous task of proving it was possible.
The researchers knew they had to recreate the red planet’s low air pressure and temperatures around negative 301 degrees Fahrenheit (negative 185 degrees Celsius).
Luckily, a test chamber at Nasa‘s Jet Propulsion Laboratory was perfectly suited for the task.
The barrel-sized device is called the Dirty Under-vacuum Simulation Testbed for Icy Environments, but scientists know it by its nickname, DUSTIE.
The researchers chilled Martian soil simulant in a container submerged within a liquid nitrogen bath.
They placed it in the DUSTIE chamber, where the air pressure was reduced to mirror the red planet’s southern hemisphere.
Carbon dioxide filled the chamber and turned from gas to ice over the next three to five hours.
After several attempts, the team achieved the necessary conditions for thick, translucent ice. A heater was set inside the chamber to warm the simulant from below, melting the ice.
Lead author Lauren Mc Keown recalled her shock when a dark plume of carbon dioxide gas emerged.
“It was late on a Friday evening and the lab manager burst in after hearing me shrieking,” Mc Keown said. “She thought there had been an accident.”
The pressurized gas tore holes in the simulant as it was expelled, scattering debris.
The team noticed how ice formed between the simulant grains before cracking it open – a possibility excluded from the Kieffer model.
Future experiments will simulate sunlight from above, rather than below, to narrow down the conditions under which “spiders” form.
Bigger questions – including whether the scars are vestiges of a different time and climate – must go unanswered for now.
Although the Curiosity and Perseverance rovers are trekking across Mars, they are far from the southern hemisphere.
Conditions on the red planet’s hemispheres are notoriously harsh.
The Phoenix lander, which touched down in the north, only lasted a few months before succumbing to the limited sunlight and punishing chill.
Here's what you need to know about the red planet...
