Mars' underground flood channels are much deeper than we thoughtS

Mars is home to some of the most chaotic terrain in our solar system, and questions behind how its assorted canyons, fissures and chasmscame to be are among the most pressing in all of planetary science. Now, newly published research reveals that Marte Vallis — one of Mars' largest geological features — is longer, and far deeper, than we ever realized — a find that could have major implications for our understanding of the planet's watery past.

Gouged across the surface of the Red Planet is a wide assortment of long, broad, and occasionally very deep stretches of ramifying "outflow channels." The majority of these mysterious Martian features are usually attributed to megafloods1 — explosive deluges triggered by a massive release of liquid water from ancient subterranean aquifers.

Megafloods are thought to have been rare, episodic events, and occurred deep in Mars' past — but some of the planet's outflow channels are actually surprisingly young; by comparing them to older subterranean straits, planetary geologists think they can paint a clearer picture of the Red Planet's geophysical past.

At roughly 1,000 kilometers in length, Marte Vallis is the largest of the channels attributed to recent outburst floods ("recent" here meaning within the last 500 million years). It is therefore of prime importance to researchers keen on understanding Mars' hydrological history.

Mars' underground flood channels are much deeper than we thought

The image above highlights the location of the Marte Vallis channel on Mars. The dashed box highlights Elysium Planitia, the planet's second-largest volcanic region, and the area shown in the 3D model below.

But exploring the vastness of Marte Vallis is tricky. Since its formation, much of the channel has been filled in by lava flow, obscuring its reaches the way sand occludes cracks in freshly laid patio bricks. The channel's true depth and length have long remained a mystery, to say nothing of the water source responsible for its initial formation.

Now, a team led by planetary scientist Gareth Morgan has used subsurface radar to produce the most accurate — and extensive — map of Marte Vallis yet: a three-dimensional reconstruction that reveals the channel to be 180 km longer and twice as deep as previously believed. The team has also identified a series of fissures — known collectively as Cerberus Fossae — as the wellspring from which the megaflood responsible for Marte Vallis originally sprung. The team's findings are published in the latest issue of Science.

Mars' underground flood channels are much deeper than we thought

Via NASA: 3D visualization of the buried Marte Vallis channels beneath the martian surface. Marte Vallis consists of multiple perched channels formed around streamlined islands. These channels feed a deeper and wider main channel. Please note the surface has been elevated, and scaled by a factor of 1/100 for clarity. The color scale represents the elevation of the buried channels relative to a martian datum (Note: the reason the values are negative is because the elevation of the surface of Mars in this region is also a negative – below average global elevation).

The subsurface radar used to make the measurement goes by SHARAD (Mars SHAllow RADar sounder), and is just one of in a compendium of awesome instruments aboard NASA's Mars Reconnaissance Orbiter, that includes the HiRISE telescope used to photograph the Curiosity rover last August as it descended through Mars' atmosphere.

According to the researchers, the data acquired by SHARAD will prove crucial to our understanding of Mars' past. "Understanding Marte Vallis is essential to our assessment of recent Mars hydrologic activity," they write, "during a period otherwise considered to be cold and dry."

Read the team's findings in the latest issue of Science.

1. This is by no means a universally accepted theory. To quote NASA, "Channels are among the more puzzling and intriguing features of the Martian surface. The most controversial aspect of the channels is whether they were formed by running water." That said, they are part of an ever-growing body of evidence that supports a wet Martian past.