March 8, 2013
Subsurface Maps Show Buried Channels Beneath The Surface Of Mars
April Flowers for redOrbit.com - Your Universe Online
For the first time ever, new maps of the subsurface of Mars show buried channels below the surface of the planet. These channels suggest evidence of flooding on a planet that has been considered by scientists to be cold and dry for the last 2.5 billion years. The young channels are located in Elysium Planitia, an expanse of plains along the equator. This region is also the youngest volcanic region on Mars. Understanding the scale and source of these channels is essential for scientists to comprehend recent hydrologic activity on the planet. This will allow them to determine if such floods could have induced climate change.The research team, which includes scientists from NASA's Goddard Space Flight Center, the Jet Propulsion Laboratory, the Planetary Science Directorate in the Southwest Research Institute and the Smithsonian Institution, published their findings in a recent issue of Science.
Gareth Morgan, a planetary scientist at the Smithsonian Institution, told the Associated Press that beyond contributions from rovers and landers, "our view of the red planet has largely been restricted to looking at the surface."
Most of the surface of equatorial region of Elysium Planitia is covered by young lava as a consequence of extensive volcanism throughout the past several hundred million years. The lava was laid down approximately 500 million years ago, a relatively short time in geologic terms. This lava covering buries evidence of the region's recent geologic history, including the source and most of the length of the 1,000 kilometer-long Marte Vallis channel system. Though little is known of Marte Vallis because of the lava, it displays a similar morphology to more ancient channel systems likely formed by the catastrophic release of ground water.
Data from NASA's Mars Reconnaissance Orbiter spacecraft's Shallow Radar (SHARAD) instrument — which can penetrate some surface features, revealing layers beneath - was used to probe beneath the surface of the lava covering Elysium Planitia, allowing the team to map the buried channels and establish that the floods originated from a now buried portion of the Cerberus Fossae fracture system. The study reveals that whatever the cause of the Martian floods, they empty the region of so much water that the surface terrain collapses, resulting in so-called "chaos terrain." The Cerberus Fossae system, with its series of parallel faults caused by volcanic activity, certainly seems to fit the name.
"What we've found is that the source of this megaflood was water deep underground that was delivered to the surface through tectonic fractures," said Morgan. "The source of the water, and the size of the outflow, had been something of a mystery, but the radar allowed us to look below the lava flows and see what existed there before."
Ars Technica reports that the main channel for the Elysium Planitia flooding was approximately 25 miles wide and at least 131 feet deep — though in some places it could be as deep as 262 feet. The only confirmed flood feature of similar size on Earth is the draining of Lake Missoula in eastern Washington State during the last glacial period. Lake Missoula, which stretches some 200 miles, broke through an ice dam several times around 15,000 years ago. Scientists estimate the entire lake drained each time in under 48 hours, digging deep channels into the hardened lava, or basalt, of the region. The Marte Vallis floods had similar effects on the Martian surface, some 3.7 to 3.1 billion years ago.
"Our findings show that the scale of erosion was previously underestimated and that channel depth was at least twice that of previous approximations," said Morgan, geologist at the National Air and Space Museum's Center for Earth and Planetary Studies. "The source of the floodwaters suggests they originated from a deep groundwater reservoir and may have been released by local tectonic or volcanic activity. This work demonstrates the importance of orbital sounding radar in understanding how water has shaped the surface of Mars."
The Mariner 9 mission in 1971 originally spotted dry channels on the Martian surface. Viking spacecraft observations later suggested the geologic features were most likely carved by water. Subsequent Mars missions have used sophisticated instruments to detail these winding channels.
National Geographic News reports that this latest finding is part of a recent "revolution in water discoveries on Mars." Along with these deep river channels, scientists have discovered gullies of still forming liquid water and salty streams that appear to flow down some crater walls during the Martian summer. Mars rover Curiosity has identified a possible stream or riverbed that once flowed into Gale Crater by examining the makeup of rock formations and rounded nearby pebbles. Unlike the Elysium Planitia megafloods that only lasted days or months, these smaller rivers ran for thousands or millions of years.
"Mars is certainly very cold and dry today, but even now it remains dynamic and certainly is not dead," Morgan said. "There are huge reservoirs of ice beneath the surface and we don't really know much about its relationship with the surface."
It is clear from the new findings that water from deep inside of Mars can and has surged to the surface through rock fractures in the relatively recent past. The research team suggests it is within the realm of possibility that another megaflood could happen in the future and that despite decades of theory, Mars may remain a geologically active planet today.