Flowing Barchan Sand Dunes on Mars

Reply Sun 22 Apr, 2012 11:32 am
Flowing Barchan Sand Dunes on Mars
Image Credit: HiRISE, MRO, LPL (U. Arizona), NASA

Explanation: When does Mars act like a liquid? Although liquids freeze and evaporate quickly into the thin atmosphere of Mars, persistent winds may make large sand dunes appear to flow and even drip like a liquid. Visible on the above image right are two flat top mesas in southern Mars when the season was changing from Spring to Summer. A light dome topped hill is also visible on the far left of the image. As winds blow from right to left, flowing sand on and around the hills leaves picturesque streaks. The dark arc-shaped droplets of fine sand are called barchans, and are the interplanetary cousins of similar Earth-based sand forms. Barchans can move intact a downwind and can even appear to pass through each other. When seasons change, winds on Mars can kick up dust and are monitored to see if they escalate into another of Mars' famous planet-scale sand storms.




This observation shows sand dunes within the Hellespontus region of Mars.

The sand appears to come from the layered mesas and knobs, features that have been eroded by powerful winds. The dunes here have a morphology indicating formative winds blowing from east to west (from right to left).

The primary indicator for this is the orientation of the barchan dunes, a dune type that on Earth has its horns in the downwind direction. Also, the steepest faces of the dunes are on the dunes’ eastern side, indicating easterly winds.

In addition to the barchans, some of the dunes are organized into a “seif,”, or longitudinal, form whereby their long axis is parallel to the wind. These are seen emanating from the sand sheets next to the mesas and knobs, as well as from some barchan horns.

Written by: Circe Verba, Nathan Bridges (18 April 2008)

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Reply Sun 29 Apr, 2012 10:55 am
Massive lava coils spotted on Mars, where everything is super-sized
Lava coils on Mars
(NASA / Associated Press By Amy Hubbard
April 27, 2012

A little bit of Hawaii has been discovered on Mars. Lava coils have been spotted on the surface of the Red Planet, but the Mars version dwarfs anything we've seen after Mauna Loa blows its stack.

The distinctive coils, spotted in a region of valleys near the planet's equator, were captured in high-resolution images by NASA's orbiter and returned to Earth for scientists to pore over. The spirals discovered in those images -- by a graduate student at Arizona State University -- are reportedly the first extraterrestrial lava coils ever identified.

"The spirals and polygonal fractures ... are similar to features seen in the more fluid lava flows on Earth, like those in Hawaii," said Ashwin R. Vasavada, deputy project scientist for the Mars Space Laboratory, in an interview Friday with the Los Angeles Times.

This is how such polygonal cracks and coils form: The surface of the lava cools and contracts. But as the lava beneath it cools more slowly, the surface splits open in a polygonal pattern. "It's not too different than the mud cracks you can find in a drying pond," Vasavada said.

Coils form when the cooling lava twists along as the lava flow moves downstream, like a whirl in a river downstream of a rock. But on Mars, "everything is larger and slower because the fluid on Mars is taffy like," he said.

Larger is right.

The spirals are up to 100 feet wide, he said, much larger than those in Hawaii, which are 1 to 2 feet wide. The super-sized Mars phenomenon was evident in a recent 12-mile-high dust devil documented on the planet's surface.

"Part of what makes studying other planets so fascinating," Vasavada said, "is to see processes we're familiar with on Earth, but with an unexpected twist because the 'ground rules' have changed."

Another striking thing about the lava patterns is that they speak to the long debate over what formed those valleys in the Athabasca Valles region of Mars in the first place -- fire or ice?

The scientist noted that "finding bits of circumstantial evidence like these spirals, which form in lava on Earth, will help solve this mystery."

It was Arizona State University graduate student Andrew Ryan who spotted the coils in images snapped by the Mars Reconnaissance Orbiter. He was analyzing the images as part of a class project, zoomed in and saw the coils.

In the April 27 issue of the journal Science, Ryan reported his findings. He told Space.com that there's no way ice could explain these patterns: They can be explained only by "lava processes," he said.

Scientists will continue to look at the implications of the cracks and spirals and the possibility of a history of water on the planet.

The Mars Science Laboratory, in fact, is on its way to Mars to plumb this mystery. The laboratory carries the Curiosity rover, which is set to land on the surface of Mars on Aug. 5. The laboratory project will follow up on the discovery of clays -- minerals that need liquid water to form -- on Mars.


Lava coils as much as 100 feet wide have been spotted on the surface of Mars, adding fuel to the debate over what formed the landscape -- fire or ice?

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