Arizona State University graduate student Andrew Ryan has discovered a new form of Martian lava flow that resembles snail or nautilus shells.
Such patterns have been found on Earth, but never before on Mars. The discovery of 269 spiral lava coils ranging from 5 to 30 meters wide in the Athabasca Valles Region is published in the journal Science.
“I was interested in Martian outflow channels and was particularly intrigued by Athabasca Valles and Cerberus Palus, both part of Elysium,” said lead author Ryan. “Athabasca Valles has a very interesting history. There’s an extensive literature on the area, as well as an intriguing combination of seemingly fluvial and volcanic features.”
Among the features are large slabs or plates that resemble broken floes of pack ice in the Arctic Ocean on Earth. In the past, a few scientists have argued that the plates in Elysium are in fact underlain by water ice.
Assessing those claims that ice was present today beneath the lava plates drove Ryan to study the area. “My initial goal was to model the nighttime infrared temperatures of the plates,” he said. “Then I became fascinated by the terrain lying between the plates and the high-centered polygonal patterns found there.” This led him to look closely at every available image of the region.
“I examined probably 100 HiRISE images of the area,” Ryan said, referring to the High Resolution Imaging Science Experiment camera on the Mars Reconnaissance Orbiter. In addition, he pored over daytime and nighttime infrared and visual images from the Thermal Emission Imaging System camera on Mars Odyssey orbiter.
On Earth, lava coils can be found on the Big Island of Hawaii, mainly on the surface of ropey pahoehoe lava flows. They have also been seen in submarine lava flows near the Galapagos Rift on the Pacific Ocean floor.
“The coils form on flows where there’s a shear stress – where flows move past each other at different speeds or in different directions,” Ryan explained. “Pieces of rubbery and plastic lava crust can either be peeled away and physically coiled up – or wrinkles in the lava’s thin crust can be twisted around.”
“Since the surface of active lava lakes, such as those on Hawaii, can have crustal activity like spreading centers do, it’s conceivable that lava coils may form there in a similar way, but at a smaller scale,” he added.
The size of Martian lava coils came as a surprise. “On Mars the largest lava coil is 30 meters across – that’s 100 feet. That’s bigger than any known lava coils on Earth,” Ryan said.
“Lava coils may be present in other Martian volcanic provinces or in outflow channels mantled by volcanic features,” Ryan concluded. “I expect that we’ll find quite a few more in Elysium as the HiRISE image coverage grows over time.”