(Left) A graph charting the depth of the Hellas depression at different points, and a topographic map of the depression. (Right) A graph charting the depth of the Galaxias Fossae depression at different points, and a topographic map of the depression. Credit: Joseph Levy/NASA
A strangely shaped depression on Mars could be a new place to look for signs of life on the Red Planet, according to a University of Texas at Austin-led study. The depression was probably formed by a volcano beneath a glacier and could have been a warm, chemical-rich environment well suited for microbial life “We were drawn to this site because it looked like it could host some of the key ingredients for habitability – water, heat and nutrients,” said Joseph Levy, University of Texas Institute for Geophysics.
The depression is inside a crater perched on the rim of the Hellas basin on Mars and surrounded by ancient glacial deposits. It first caught Levy’s attention in 2009, when he noticed crack-like features on pictures of depressions taken by the Mars Reconnaissance Orbiter that looked similar to “ice cauldrons” on Earth, formations found in Iceland and Greenland made by volcanos erupting under an ice sheet. Another depression in the Galaxias Fossae region of Mars had a similar appearance.
“They’re concentrically fractured so they look like a bulls-eye. That can be a very diagnostic pattern you see in Earth materials,” said Levy, Portland State University. But it wasn’t until this year that he and his team were able to more thoroughly analyze the depressions using stereoscopic images to investigate whether the depressions were made by underground volcanic activity that melted away surface ice or by an impact from an asteroid.
Timothy Goudge et al used pairs of high-resolution images to create digital elevation models of the depressions that enabled in-depth analysis of their shape and structure in 3-D. “…we were able to measure not just their shape and appearance, but also how much material was lost to form the depressions. That 3-D view lets us test this idea of volcanic or impact,” Levy said. The analysis revealed that both depressions shared an unusual funnel shape, with a broad perimeter that gradually narrowed with depth.
“That surprised us and led to a lot of thinking about whether it meant there was melting concentrated in the center that removed ice and allowed stuff to pour in from the sides. Or if you had an impact crater, did you start with a much smaller crater in the past, and by sublimating away ice, you’ve expanded the apparent size of the crater,” Levy said.
After testing formation scenarios for the two depressions, they found that they probably formed in different ways. The debris spread around the Galaxias Fossae depression suggests that it was the result of an impact – but the known volcanic history of the area still doesn’t rule out volcanic origins. In contrast, the Hellas depression has many signs of volcanic origins. It lacks the surrounding debris of an impact and has a fracture pattern associated with concentrated removal of ice by melting or sublimation.
The interaction of lava and ice to form a depression would be an exciting find because it could create an environment with liquid water and chemical nutrients, both ingredients required for life on Earth. He said that the Hellas depression and, to a lesser extent, the Galaxias Fossae depression, should be kept in mind when looking for habitats on Mars. “These features do really resemble ice cauldrons known from Earth, and just from that perspective they should be of great interest,” Pedersen,volcanologist at the University of Iceland said. “Both because their existence may provide information on the properties of subsurface material – the potential existence of ice — and because of the potential for revealing ice-volcano interactions.” http://news.utexas.edu/2016/11/10/mars-funnel-could-support-alien-life
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