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Mars' 'Raindrop' Sand Dunes Swarm

Raindrop-shaped sand dunes enriched with olivine swarm inside Mars' Copernicus Crater.

Mars is a funny place. It is both familiar and very alien. Take these sand dunes for example.

There are countless examples of dunes on Mars -- features created by the transport of the fine Martian regolith blowing in the wind. The physics behind this movement of material is surprisingly complex, but not too dissimilar to the sand dunes you might find on a terrestrial beach or desert.

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However, on analyzing a swarm of dunes inside Mars' Copernicus Crater, the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board NASA's Mars Reconnaissance Orbiter (MRO) picked out the presence of olivine, a mineral that forms in the presence of water. The High Resolution Imaging Science Experiment (HiRISE) was then used for follow-up observations. The tiny olivine particles have been blown in the wind, collecting in these "raindrop" shaped dunes.

Commonly, Mars dunes take the shape of barchan dunes we find on Earth. Barchans are characterized by a smooth windward-facing edge, with a receding steep slope, often creating a horn-like structure on the downward slope. As can be seen in the image left, some of the dunes do look like classic barchans, whereas many retain the droplet shape.

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"Olivine-rich dunes are very rare on Earth, as olivine rapidly weathers to clays in a wet environment," writes Alfred McEwen, University of Arizona planetary scientist and principal investigator of HiRISE. "There is also olivine-rich bedrock in the central peaks of Copernicus Crater on the Moon."

Observations like these not only help us piece together the puzzle of Mars' water history, it also gives us a clue about the active atmospheric and geologic processes that continually shape the red planet's surface.

The dark features here look like raindrops on Mars, but are actually sand dunes rich in the mineral olivine.

MAHLI Power

Since NASA's Mars Science Laboratory (MSL) rover Curiosity landed on the red planet, each sol (a Martian "day") of the mission sees a flood of new photographs from Aeolis Palus -- the plain inside Gale Crater where Curiosity landed on Aug. 5. In September 2012, mission controllers sent the command for Curiosity to flip open the dust cap in front of the robotic arm-mounted Mars Hand Lens Imager (MAHLI). Until that point, the semi-transparent dust cap only allowed MAHLI to make out fuzzy shapes -- although it did a great job imaging Curiosity's "head" and it is also famous for capturing Curiosity's first color photograph. But since the true clarity of MAHLI has been unleashed, we've been treated to some of the most high-resolution views of the rover, Martian landscape and, most importantly, we've seen exactly what MAHLI was designed to do: Look closely at Mars rocks and dirt, assembling geological evidence of potential past habitability of Mars.

The Business End

Curiosity is armed with 17 cameras and MAHLI is designed to capture close-up photos of geological samples and formations as the rover explores. MAHLI was designed and built by Malin Space Science Systems and is analogous to a geologist's hand lens -- only a lot more sophisticated. Its high-resolution system can focus and magnify objects as small as 12.5 micrometers (that's smaller than the width of a human hair!). This photograph captured by the rover's Mastcam shows the MAHLI lens (with dust cap in place) in the center of the end of Curiosity's instrument-laden robotic arm.

Lights On!

To aid its studies, MAHLI is equipped with four LEDs to light up the imager's samples.

Mars Dirt

The first photograph to be returned from MAHLI without the dust cover in place was received on Sol 33 (Sept. 8) of Curiosity's mission. Shown here is a view of the ground immediately in front of the rover. Although this photo was a test, mission scientists were able to do a very preliminary study of the large "pebble" at the bottom of the picture: "Notice that the ground immediately around that pebble has less dust visible (more gravel exposed) than in other parts of the image. The presence of the pebble may have affected the wind in a way that preferentially removes dust from the surface around it," they wrote.

How Did Lincoln Help MAHLI?

On Sol 34 (Sept. 9), MAHLI was aimed at Curiosity's calibration target. This target is intended to color balance the instrument and provide a "standard" for mission scientists to refer to. The 1909 Lincoln penny was provided by MAHLI's principal investigatory Ken Edgett. Using a penny as a calibration target is a nod to geologists' tradition of placing a coin or some other object of known scale as a size reference in close-up photographs of rocks, says the MSL mission site.

Dusty Wheels

Although MAHLI will be used to examine microscopic scales, it is showing its prowess at generating some spectacular high-definition views of the rover. Shown here is a mosaic of Curiosity's three left-side dusty wheels.

Hazard Avoidance Cameras

Hazard Avoidance Cameras, or Hazcams, have become "standard issue" for the last three rovers to land on Mars. Mounted on the front and back of rovers Opportunity, Spirit and Curiosity, these small cameras provide invaluable information about the terrain and potential hazards surrounding the rovers. These cameras are not scientific cameras -- they are engineering cameras. Shown here, MAHLI has imaged the four front Hazcams on Curiosity. Interestingly, it was these cameras who returned Curiosity's first dusty image after touch down in August.

Underbelly

Using the flexibility of the robotic arm, MAHLI was able to check the underside of Curiosity. As the camera can focus on objects from 0.8 inch (2.1 centimeters) to infinity, MAHLI has incredible versatility allowing mission controllers to focus on the very small features of Mars to checking the health of the rover to viewing the impressive vistas beyond.

Mystery Object

In October 2012, the Internet was abuzz with speculation about a "mystery object" lying beneath the rover during digging operations at "Rocknest." Sadly, after studying the translucent object, mission scientists deduced that it wasn't anything native to the alien environment, it was actually a piece of plastic that had fallen from Curiosity. Yes, Curiosity is littering the red planet.

Digging In

The MAHLI camera was very attentive while Curiosity dug trenches in the Mars soil at "Rocknest."

Mars Flower?

In early 2013, MAHLI snapped another curious photo. This time, after driving to a rocky outcrop at a location dubbed "Yellowknife," the camera picked out what appeared to be some kind of organic-looking object embedded in the rock. Nope, it's not a Mars "flower" -- more likely it's a concentration of minerals.

Cheese!

In what has become an iconic photo of Curiosity, MAHLI was commanded to capture dozens of high-resolution pictures of the rover. Like an "arms length" shot you may have in your Facebook profile, Curiosity did the same, composing a mosaic of pics taken with its outstretched robotic arm.

Curiosity Cleans Up!

The Mars rover isn't only a scientific superstar, it also has a talent for cleaning. This circular pattern on a Mars rock was brushed aside by Curiosity's Dust Removal Tool (DRT), helping the rover carry out analysis of the rock surface beneath the layer of dirt.