May 13, 2014
New Study Finds That Lava Carved The Giant Valleys Of Mars
April Flowers for redOrbit.com - Your Universe Online
In 1877, Giovanni Schiaparelli of Italy first described what he called "canali" on the surface of Mars. These straight landforms on the Martian equatorial region form a conspicuous net-like system of deep gorges called the Noctis Labyrinthus, which is clearly visible. Noctis Labyrinthus leads into the even larger Valles Marineris canyon, which is 2500 miles long, 125 miles wide and 4 miles deep. Together, these two systems would span the United States from the east coast to the west coast.
The Martian canals resemble terrestrial water-formed canyons, leading most scientists to assume that huge flows of water sometime in the ancient history of the planet would have been required to carve the canals into the Martian surface. Other scientists believed that tectonic activity created the largest rift valley to be found on any planet in our Solar System.
A new study from ETH Zurich geoscientist Giovanni Leone, however, suggests that lava, rather than water or tectonic plate activity, cut the gigantic valleys into the red planet's landscape. His findings were published in a recent issue of the Journal of Volcanology and Geothermal Research.
Leone, a specialist in planetary volcanism in the research group of ETH professor Paul Tackley, said that the assumptions of water or tectonic movement were far off the mark. According to his research, only lava flows would have the force and mass necessary for such formations.
Leone has performed an extensive study of the structure of these canyons and their outlets into the Ares Vallis and the Chryse Planitia — a huge plain on the low northern latitudes of the planet. He analyzed thousands of high-resolution images from a variety of Mars probes — including images from NASA's Mars Reconnaissance Orbiter that are available on the USGS image databases — to reach what he considers an unequivocal conclusion.
“Everything that I observed on those images were structures of lava flows as we know them on Earth,” he emphasizes. "The typical indicators of erosion by water were not visible on any of them.”
He can't, however, completely rule out water as a final formative force. Though scarce, evidence of water — such as salt deposits in locations where water evaporated from the ground or signs of erosion on the alluvial fans of the landslides — are still observable. “One must therefore ask oneself seriously how Valles Marineris could have been created by water if one cannot find any massive and widespread evidence of it.” Another challenge to the water formation theory, according to Leone, is that he could not find an explanation for where such massive amounts of water might have originated.
Leone's model demonstrates the formation history of the canyons from the source to the outlets, identifying the volcanic region of Tharsis as the source of the lava flow. Tharsis is also the location of the initial lava tubes that stretched to the edge of Noctis Labyrinthus.
"Pit chains," a chain of almost circular holes, formed when the pressure from an eruption subsided and the lava tube ceiling partially collapsed. The tube ceilings completely collapsed when lava flowed through the tubes again, forming deep V-shaped troughs. Mechanical erosion, and the melting of ground and rim material, allowed the mass of lava to carve a deeper and broader bed to form canyons. The rims of this bed slipped, and were consumed by subsequent lava flows. “The more lava that flowed, the wider the canyon became,” says Leone.
Leone's theory is upheld with height measurements from different Mars probes. In the valleys of Noctis Labyrnthus, the typical V-shape of "young" lava valleys can be observed where the tub ceilings have completely collapsed. However, the upper rims of these valleys are the same height, which they would not be if tectonic forces had formed them. The water formation theory is likewise undermined by the fact that such erosion would have taken tens of millions of cubic kilometers of water (approximately three billion US gallons of water per ten million cubic kilometers). If the canyons had been formed by water, nearly all the atmospheric water of all the ages would have had to be concentrated on the Noctis Labyrinthus region alone. Leone notes that on Mars the atmosphere is too thin, and the temperatures too cold, for surface water to stay liquid long enough to form a river of sufficient size and force.
The implications of Leone's findings are far-reaching. “If we suppose that lava formed the Noctis Labyrinthus and the Valles Marineris, then there has always been much less water on Mars than the research community has believed to date,” he says. The rain in Mars' past would have been insufficient to erode such deep, huge gorges, and the shallow ocean north of the equator was most likely much smaller than imagined. According to Leone, it would have only existed around the North Pole—making the likelihood that life existed on the planet, now or in the past, much lower.
Leone says it is possible that the still existing lava tubes could harbor living organisms, as they would offer protection from the UV rays that bombard the Martian surface. He suggests that in a future mission to Mars, a rover could be sent through a hole in the ceiling of a tube to search for evidence of life.
“Suitable locations could be determined using my data,” he says.
Leone's findings are controversial, and could result in a total change in dogma. The majority of studies done in the last two decades have focused on the question of water on Mars, and how this water could have formed the canals. Leone is not the first to posit lava as the formative force, in 1977 another researcher theorized that Vallis Marineris might have been formed by lava, but his ideas never caught hold. According to Leone, this is due to scientific tunnel vision locked onto the prevailing mainstream research. Science can only benefit, he says, from considering alternative approaches to the question.
“I expect a spirited debate,” he says. “But my evidence is strong.”