The spacecraft took numerous images during the past few years that showed channels attributed to catastrophic flooding in the past 500 million years. During this period, Mars had been otherwise considered cold and dry. These channels are essential to understanding the extent to which recent hydrologic activity prevailed during such arid conditions. They also help scientists determine whether the floods could have induced episodes of climate change.
The estimated size of the flooding appears to be comparable to the ancient mega-flood that created the Channeled Scablands in the Pacific Northwest region of the United States, in eastern Washington.
“Our findings show the scale of erosion that created the channels previously was underestimated, and the channel depth was at least twice that of previous approximations,” said Gareth Morgan from the National Air and Space Museum’s Center for Earth and Planetary Studies in Washington, D.C. “This work demonstrates the importance of orbital sounding radar in understanding how water has shaped the surface of Mars.”
The channels lie in Elysium Planitia, an expanse of plains along the martian equator and the youngest volcanic region on the planet. Extensive volcanism throughout the past several hundred million years covered most of the surface of Elysium Planitia, and this buried evidence of Mars’ older geologic history, including the source and most of the length of the 620-mile-long (1,000 kilometers) Marte Vallis channel system. To probe the length, width, and depth of these underground channels, the researchers used the Mars Reconnaissance Orbiter’s Shallow Radar (SHARAD).
Marte Vallis’ morphology is similar to more ancient channel systems on Mars, especially those of the Chryse Basin. Many scientists think the Chryse channels likely were formed by the catastrophic release of groundwater, although others suggest lava can produce many of the same features. In comparison, little is known about Marte Vallis.
With the SHARAD radar, the team was able to map the buried channels in 3-D with enough detail to see evidence suggesting two different phases of channel formation. One phase etched a series of smaller branching, or “anastomosing,” channels that are now on a raised “bench” next to the main channel. These smaller channels flowed around four streamlined islands. A second phase carved the wide deep channels.
“In this region, the radar picked up multiple ‘reflectors,’ which are surfaces or boundaries that reflect radio waves, so it was possible to see multiple layers,“ said Lynn Carter from NASA’s Goddard Space Flight Center in Greenbelt, Maryland. “We have rarely seen that in SHARAD data outside of the polar ice regions of Mars.”
The mapping also provided sufficient information to establish the floods that carved the channels originated from a now-buried portion of the Cerberus Fossae fracture system. The water could have accumulated in an underground reservoir and been released by tectonic or volcanic activity.
“While the radar was probing thick layers of dry, solid rock, it provided us with unique information about the recent history of water in a key region of Mars,” said Jeffrey Plaut of NASA’s Jet Propulsion Laboratory in Pasadena, California.