Image of the Day: The Ancient “Riverbeds” of Mars –Formed by Water or Lava?

MarsAncientRiverBed

David Leverington, an associate professor in the Department of Geosciences at Texas Tech, believes that what we view as the largest ancient riverbeds on Mars most likely were created not by water, but by massive, fast-moving, low-viscosity lava flows that seared the early planet, nixing the popular view that the channels were created by water that reinforced the belief that life on the planet may be or once was possible.  Life on Mars could have developed, he said, though the severe volcanic activity that created the largest outflow channels might have hampered the planet’s ability to support complex organisms living on the surface.


Leverington employed high-resolution photographs and mineralogical data to help lay out his theory for why lava is a much more likely culprit for creating the largest class of the outflow channels and canyons, which can stretch up to 1,800 miles.

“This paper highlights the strengths and weaknesses of the two theories that these outflow channels were formed by volcanic or water activity,” Leverington wrote in his study that appears in Geomorphology, which will publish in September 2011. “Many scientists realize there are issues with aqueous interpretations of these channels. They recognize that if these systems formed by giant subsurface flows of water, there would need to have been extraordinarily high ground permeability, up to a million or more times greater than what we’d expect for the crust of the Earth, just to allow sufficient amounts of water to make it to the outflow locations and erupt to the surface.”

Most of Mar's water appears to be trapped at the poles and at higher latitudes in the form of ice, Leverington said. Most modern theories on the creation of the largest channel systems center on the action of surface floodwaters pushed up from enormous subsurface aquifers. 

“What we know about Mars’ water is that it’s primarily in the solid state and concentrated at higher latitudes,” he said. “We see large concentrations at the polar icecaps. Various measurements also have been made to infer the presence of water at high latitudes to mid latitudes where there appears to be ice frozen below the surface. An important question has recently arisen: Is there much more water on Mars than this? While there is a considerable volume of water on Mars, it may not be sufficient to have driven the kinds of channel-forming processes many believe happened.”

The Martian outflow channels superficially resemble channels on Earth that formed by floods from giant glacial lakes. However, unlike Earth’s water-formed channels, Leverington said the large Martian canyons do not feature obvious river deposits and don’t terminate in delta-like, sediment-laden mouths, such as at the end of the Mississippi River, but fade into vast plains composed of volcanic basalt.

“We see abundant evidence for past eruptions of lava at the heads of these large systems, for flows along these systems and for extraordinarily large volumes of lava at the mouths of these systems,” he said. “These characteristics are very similar to what we see at volcanic channels on the moon and on Venus. There’s really no known process for the rapid eruption of large amounts of water from aquifers to form channels that are thousands of miles long. We do have evidence of this happening through past volcanic processes on the moon and Venus.”

These kinds of channel-forming volcanic flows wouldn’t have been like anything ever seen by humans on Earth, Leverington said, though evidence suggests these types of massive lava flows could have occurred very early in our planet’s history.

“If we look at modern mineralogy of ancient materials exposed on the surface of Mars, we see some evidence that water was present in the vapor or liquid state very early on,” Leverington said. “We also know of many materials that should have been altered by wet conditions quite readily that haven’t been greatly altered, though they have been exposed since quite early in Mars’ history. Some ancient exposed bedrock contains large amounts of iron-rich olivine, and that has not been altered in the past 3.5 billion years. That would suggest that most of Mars history has been extraordinarily dry.

“Surface conditions were likely to have been relatively wet in large regions only in Mars’ earliest development stages. These wet stages pre-date the development of the large outflow channels on Mars.”

“There’s still the potential for life to have developed and even flourished in the earliest and wettest stages of Mars’ history,” Leverington said. “Simple life forms, such as bacteria-like organisms, could have lingered in the subsurface under the dry conditions that ultimately became widespread. But if the large outflow channels formed through volcanic mechanisms rather than substantial water flow, that mainly restricts the environments conducive to the development of life to the earliest stages of that planet’s history.”

The image below is the Kasei Valles, a circum-Chryse outflow channel, which flowed into the Chryse Planitia. Credit: NASA/Texas Tech.

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