The surface of Mars exhibits numerous lava flows and other signs of effusive volcanism. Although models suggest that explosive volcanism should also have produced extensive deposits, direct evidence for large-scale explosive volcanism has been scarce.
A new study by Briony Horgan and James F. Bell III at Arizona State University on the mineralogy of dark regions covering more than ten million square kilometers in the northern hemisphere of Mars has revealed that these regions are dominantly composed of glass.
Horgan and Bell used the European Space Agency's Mars Express orbiter to re-examine light radiated from the martian plains. They determined that the unusual readings were caused by sand composed of glass. "We're actually seeing glass particles, like glass sand," Horgan said. "The only way to create an extensive glassy deposit like that is through explosive volcanism," he added. "This is the first direct evidence on Mars for explosive volcanism on a planetary scale."
The glass is most likely volcanic glass produced during explosive eruptions, and potential sources include volcano-ice interactions in the northern lowlands as well as ash deposits from the large martian shield volcanoes. The glass deposits also exhibit signs of weathering, indicating widespread interactions with liquid water. Under the hyper-arid climatic conditions Mars has experienced over the past three billion years or more, the most likely source of this water is melting ice or snow.
Such geological features are not unique to Mars. Iceland boasts thousands of square miles of volcanic desert dominated by glass sand.
These results suggest that explosive volcanism may be a major source of sediments on Mars, and that limited liquid water has been present at the surface of Mars even under long-term hyper-arid conditions.
The three-dimensional image at the bottom of the page of the Nili Fossae region of Mars Northern Hemisphere shows a type of minerals called phyllosilicates (in magenta and blue hues) concentrated on the slopes of mesas and along canyon walls. The abundance of phyllosilicates shows that water played a sizable role in changing the minerals of a variety of terrains in the planet's early history.
The northern highlands are hundreds to thousands of miles from known volcanoes, however, which has left scientists puzzled. The glass sand could provide a valuable clue. Because it requires ice or water to form, the subglacial lakes they suggest could solve part of the distribution problem.
Though the water would initially be contained - and ripe for life - eventually it could break free of the walls containing it, creating enormous floods across the lowlands.
"This would be similar to some of the catastrophic floods people have talked about for Mars."The presence of glass sand, and their requirement of water to form, bring a clearer understanding to the geology of the red planet, and a more concrete suggestion on where to look for life. "It's the first time we've really seen evidence for ice-related alterations on Mars," Horgan said.
The image at the top of the page shiws the glass-rich sand dunes like these found just south of the north polar ice cap could cover much of Mars.
The Daily Galaxy via astrobio.net and http://www.geosociety.org/news/pr/12-24.htm -- Widespread weathered glass on the surface of Mars Briony Horgan and James F. Bell III, School of Earth and Space Exploration, Arizona State University, Tempe, Arizona 85281, USA. Posted online 26 March 2012; doi: 10.1130/G32755.1.
Image Credit: NASA/JPL/The Johns Hopkins University Applied Physics Laboratory/University of Arizona/Brown University and Credit: NASA/JPL/University of Arizona
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