Gigantic lava spirals wreck Mars ice valley theory
Student goes looking for water, finds yet more rock
A boffin-in-training has discovered huge snail-like coils of lava on Mars that suggest the flow of molten rock formed valleys on the surface rather than ice.
For years scientists have wondered if parts of the Red Planet were long ago shaped by frozen water, the presence of which supports hope that there is or was life on the seemingly barren dust world.
In particular, the Athabasca Valles and Cerberus Palus regions in the Elysium volcanic province on Mars have fuelled hypotheses that their large slabs resemble broken floes of pack ice in the Arctic Ocean on Earth and may actually have water underneath them.
While searching for signs of ice, first-year graduate student Andrew Ryan found instead the telltale spirals that show where lava once flowed in different directions.
"The coils form on flows where there's a shear stress - where flows move past each other at different speeds or in different directions. 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," Ryan of Arizona State University explained.
He pored over around 100 HiRISE images of the area snapped by NASA's Mars Reconnaissance Orbiter as well as day and night infrared and visual images from the Thermal Emission Imaging System.
"One evening, I was making a second pass over the HiRISE images when I first noticed puzzling spiral patterns in an image near the southern margin of Cerberus Palus," Ryan said.
"The coils become noticeable in the full-resolution HiRISE image only when you really zoom in. They also tend to blend in with the rest of the light-grey terrain - that is, until you stretch the contrast a bit.
"I don't find it surprising that these were overlooked in the past. I nearly missed them too," he added modestly.
A few lava coils have been found on Earth on Hawaii and near the Galapagos Rift on the Pacific Ocean floor, but they are quite rare and this is the first time they've been spotted on Mars.
The Martian coils are also interesting because of their size. The largest is 30 metres across, much bigger than any documented spirals on Earth. Ryan's study was published in today's Science journal. ®