Dust devils on Mars

Dust devils on Mars

NASA's Curiosity Mars rover has begun a second campaign of investigating active sand dunes on the northwestern flank of Mount Sharp, inside the 160 km (100 miles) wide Gale Crater. The rover also has been observing whirlwinds carrying dust and checking how far the wind moves grains of sand in a single day's time.

Gale Crater observations by NASA's Mars Reconnaissance Orbiter have confirmed long-term patterns and rates of wind erosion that help explain the oddity of having a layered mountain in the middle of an impact crater.

"The orbiter perspective gives us the bigger picture - on all sides of Mount Sharp and the regional context for Gale Crater. We combine that with the local detail and ground-truth we get from the rover," said Mackenzie Day of the University of Texas, Austin, lead author of a research report in the journal Icarus about wind's dominant role at Gale.

The combined observations show that wind patterns in the crater today differ from when winds from the north removed the material that once filled the space between Mount Sharp and the crater rim. Now, Mount Sharp itself has become a major factor in determining local wind directions. Wind shaped the mountain; now the mountain shapes the wind.

On recent summer afternoons on Mars, navigation cameras aboard NASA's Curiosity Mars rover observed several whirlwinds carrying Martian dust across Gale Crater. Dust devils result from sunshine warming the ground, prompting convective rising of air. All the dust devils were seen in a southward direction from the rover. Timing is accelerated and contrast has been modified to make frame-to-frame changes easier to see. Credit: NASA/JPL

This month, the rover is investigating a type of sand dune that differs in shape from dunes the mission investigated in late 2015 and early 2016. Crescent-shaped dunes were the feature of the earlier campaign - the first ever up-close study of active sand dunes anywhere other than Earth. The mission's second dune campaign is at a group of ribbon-shaped linear dunes.

"In these linear dunes, the sand is transported along the ribbon pathway, while the ribbon can oscillate back and forth, side to side," said Nathan Bridges, a Curiosity science team member at the Johns Hopkins University Applied Physics Laboratory in Laurel, Maryland.

The season at Gale Crater is now summer, the windiest time of year. That's the other chief difference from the first dune campaign, conducted during less-windy Martian winter.

"We're keeping Curiosity busy in an area with lots of sand at a season when there's plenty of wind blowing it around," said Curiosity Project Scientist Ashwin Vasavada of NASA's Jet Propulsion Laboratory, Pasadena, California. "One aspect we want to learn more about is the wind's effect on sorting sand grains with a different composition. That helps us interpret modern dunes as well as ancient sandstones."

Before Curiosity heads farther up Mount Sharp, the mission will assess movement of sand particles at the linear dunes, examine ripple shapes on the surface of the dunes, and determine the composition mixture of the dune material, NASA reports.

Shifting sand and 'dust devils'

Images taken one day apart of the same piece of ground, including some recent pairs from the downward-looking camera that recorded the rover's landing-day descent, show small ripples of sand moving about 2.5 cm (1 inch) downwind.

Meanwhile, whirlwinds called "dust devils" have been recorded moving across the terrain in the crater, in sequences of afternoon images taken several seconds apart.

Credit: NASA/JPL-Caltech/TAMU

After completing the planned dune observations and measurements, Curiosity will proceed southward and uphill toward a ridge where the mineral hematite has been identified from Mars Reconnaissance Orbiter observations. The Curiosity science team has decided to call this noteworthy feature the "Vera Rubin Ridge," commemorating Vera Cooper Rubin (1928-2016), whose astronomical observations provided evidence for the existence of the universe's dark matter.

As Curiosity focuses on the sand dunes, rover engineers are analyzing results of diagnostic tests on the drill feed mechanism, which drives the drill bit in and out during the process of collecting sample material from a rock. One possible cause of an intermittent issue with the mechanism is that a plate for braking the movement may be obstructed, perhaps due to a small piece of debris, resisting release of the brake. The diagnostic tests are designed to be useful in planning the best way to resume use of the drill.

Featured image credit: NASA/JPL-Caltech/TAMU

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