These Spiders from Mars are in Fine Araneiform

James Maynard
Mar 24 · 4 min read

Explaining the Spiders from Mars — one of the strangest oddities of the Red Planet

Spiders from Mars seen in 2011 by the HiRISE instrument onboard the Mars Reconnaissance Orbiter (MRO). Image credit: NASA/JPL/UArizona

Mars is a world alive with mysteries and questions. One of the oddest is the so-called spiders from Mars, one of the strangest features on the surface of this tawny world.

Known as araneiforms, these spiders from Mars are likely the result of dry ice — frozen carbon dioxide — sublimating (turning directly from solid to vapor) within the Martian crust, a new study out of Trinity College Dublin finds.

“This unique geomorphic mechanism is hypothesised to be the cause of the dendritic, branching, spider-like araneiform terrain and associated fans and spots — features which are native to Mars and have no Earth analogues,” researchers describe in an article published in the journal Scientific Reports.

Unlike Earth, the thin atmosphere of Mars consists largely of carbon dioxide, which partially freezes into dry ice at the Martian poles each winter.

“In the summer the ice will disappear into the atmosphere, and we will see just the channels of ghostly spiders carved in the surface. This is truly Martian terrain — this type of erosion does not take place anywhere naturally on Earth because our climate is too warm,” Candy Hansen writes for the University of Arizona.

Another look at araneiforms on Mars, taken by HiRISE. Image credit: NASA/JPL/UArizona

Araneiforms can appear at the southern pole of Mars as the Sun starts to warm the frozen ice caps. The strange features come in several varieties, including fat spiders that measure about 50 meters (165 feet) in diameter, thin spiders which can reach 100 km (330 feet) across, and starburst araneiforms which can stretch an entire kilometer (six-tenths of a mile) from side to side.

“These patterns are fractal, resemble tree branches and are found on Earth in systems… such as river networks, fork lightning strikes and even nerve endings in the human brain,” researchers describe in Scientific Reports.

“Ziggy played guitar, jamming good with Weird and Gilly,
and the Spiders from Mars.
He played it left hand, but made it too far,
became the special man, then we were Ziggy’s Band…”
- David Bowie, Ziggy Stardust

Researchers utilized the the Open University Mars Simulation Chamber to determine if structures like the spiders from Mars could form from the sublimation of dry ice in a simulated Martian atmosphere.

The team drilled holes in large blocks of dry ice and, using a claw, lowered them onto beds of tiny glass spheres inside chambers filled with a low-pressure atmosphere simulating Mars.

The Mars simulation chamber and the carnival-like hook system that lowered dry ice onto beds of glass beads. Image credit: Open University

When the blocks hit the much-warmer sandy beds, a process known as the Leidenfrost effect kicked in, forming a layer of gaseous carbon dioxide. This gas rose through the hole, and was measured by instruments.

In every case, spider patterns like those seen on Mars were created by the process. Researchers used several sizes of spheres in the beds, finding smaller grains produced greater numbers of branches.

“The experiments show directly that the spider patterns we observe on Mars from orbit can be carved by the direct conversion of dry ice from solid to gas. It is exciting because we are beginning to understand more about how the surface of Mars is changing seasonally today,” explains Dr. Lauren McKeown, who led this work during her PhD study at Trinity, currently at the Open University.

This process on Mars may be caused by sunlight penetrating the translucent ice, and heating the underlying terrain. This would produce a gaseous layer of carbon dioxide that would build up until pressures cracked the ice, allowing gas to escape, forming the spider-like patterns.

This study could help researchers learn more about other worlds where an icy surface meets a thin atmosphere such as Jupiter’s ocean moon Europa, and Enceladus, in orbit around Saturn.

Robotic explorers continue to map and study Mars, preparing for a time in the near future when humans will begin to populate the Red Planet.

When humans do set boots on Mars, we may just bring along our own spiders in space.

James Maynard is the founder and publisher of The Cosmic Companion. He is a New England native turned desert rat in Tucson, where he lives with his lovely wife, Nicole, and Max the Cat.

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