The secret behind Mars’s strange ‘spider’ formations

Discovered in 2003, "araneiform" formations on Mars have been recreated in the laboratory, confirming their link to carbon dioxide ice

High-resolution images preserved by orbiters around Mars in 2003 showed a landscape that might have been lifted directly from the screenplay of a science fiction movie. The involved formations had been termed “araneiform terrain“, and to state it mildly, they were like nothing more than giant spiders etched into the Martian surface, the instant magnets for media attention. They appear almost like deep scars, carved into the red skin of Mars, with some of these “spiders” stretching over half a mile from end to end in a web of “legs” radiating from a central point, especially in the southern hemisphere.

To an undiscerning eye, these formations give the impression of the aftermath of some cataclysmic event long ago or, for those of even more fertile imagination, the remains left from eons-dead Martian life. The reality behind such patterns kept scientists guessing for decades. It is only recently that the mystery has been solved: the culprit involved is carbon dioxide.

Carbon dioxide: the architect of martian spiders

In this season, the ground is covered by layers of CO₂ ice. During spring, the sun starts heating the ground and, in turn, causes sublimation of the ice. The gas trapped underground builds up enough pressure to fracture the ice and then erupts upwards, carrying dust and sand with it, to form these complex patterns.

The mystery behind martian spiders’ formation

To test that hypothesis, a NASA team simulated Martian conditions in a lab using the DUSTIE chamber-a controlled environment in which to create the low temperatures and atmospheric pressure typical of the Red Planet. Place some CO₂ ice on a sample of Martian soil and heat it from below, and presto. Just those same formations developed, confirming the role of the gas in creating these “spiders.”

A Seasonal Phenomenon Specific to Mars Curiously enough, these features are found only in the southern hemisphere and strictly in the Martian spring, thereby underlining the fact that the process is intimately interlinked with seasonal changes on the planet. Understanding this mechanism better may one day be crucial for future exploratory missions so as to enable us to judiciously select the most harmless landing sites for probes, far from these hidden giants beneath the surface.

But this much is sure: with every new secret that we discover on Mars, we are reminded of the fantastically surprising and, in equal measure, utterly unpredictable universe we are a part of.

Source: The Planetary Science Journal