A Glimpse of Channels Hidden Under Mars' Surface

Channels that run beneath the surface of Mars, evidence of a time when the planet was full of water, have mostly remained mysterious to NASA researchers. For instance, Marte Vallis, a 1000-kilometer (621-mile) channel near the planet's equator, has been impossible to study because it is buried beneath some of the youngest lava flows on the planet.

Now, scientists are learning to look beneath the surface. A team led by the Smithsonian Institution's Gareth Morgan has used the Shallow Subsurface Radar?known as SHARAD?on board the NASA Mars Reconnaissance Orbiter to probe the Marte Vallis.

SHARAD, provided by the Italian Space Agency and operational since November 2006, studies the surface of Mars by sending out a 15?25 MHz frequency band. Its antenna captures the radar wave as it returns. Some of the radar bounces back after hitting the surface, but other frequencies in the band will make it through to the channel, reflecting off its base instead. By measuring the time delay, researchers can determine what kind of material they've hit (such as dense rock, liquid water, or ice) and map the topography of the planet.

SHARAD is designed to cut as deep as 1 km, as it's under the surface that researchers hope to find ice. Morgan tells PM that the returning echoes give the researchers tracks of data across several hundreds of kilometers, producing slices into the subsurface and providing cross-sectional images. After filtering out noise and other interference, they have a picture of the subsurface.

"It's hard to look at these and see where the channel is," he said, "but we took each slice and mapped out where we thought we saw channels. Then, when we used software to spatially align the slices, we could see where the channels we'd marked were lining up from track to track."

3-D visualization of the buried Marte Vallis channels beneath the Martian surface. Marte Vallis consists of multiple perched channels formed around streamlined islands. Credit: NASA

Once they'd produced a final image, the team made several new discoveries about the channel. The channels proved to be twice as deep (18 meters, or about 60 feet) than previously assumed, and the system was much more complex than anyone had guessed. Most important, Morgan and his team found the source of the channel, which had been a cause of debate. Some scientists thought the water originated from a standing body, like a lake, that overflowed, while others though it came from the Cerbrus Fossae, a series of fissures. It was thought that the fissures never actually cut across the path of the channel, but SHARAD showed that it did a full 180 km (112 miles) to the east.

Until now, SHARAD's main purpose has been to seek out water and ice on Mars, not to explore its subsurface tunnels and caverns. Morgan hopes his work, published today in Science, will change that.

"This kind of 3D reconstruction hasn't been done with SHARAD previously," he said. "This shows that we can use this radar to look for buried channels." That, he says, is the next step in understanding the hydrology of Mars.

Source: http://www.popularmechanics.com/science/space/moon-mars/a-glimpse-of-channels-hidden-under-mars-surface-15185099?src=rss

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