Blue Mars

Image Credit: NASA/JPL/Cornell

Endurance Crater’s Dazzling Dunes

As NASA’s Mars Exploration Rover Opportunity creeps farther into “Endurance Crater,” the dune field on the crater floor appears even more dramatic. This false-color image taken by the rover’s panoramic camera shows that the dune crests have accumulated more dust than the flanks of the dunes and the flat surfaces between them. Also evident is a “blue” tint on the flat surfaces as compared to the dune flanks. This results from the presence of the hematite-containing spherules (“blueberries”) that accumulate on the flat surfaces.

Sinuous tendrils of sand less than 1 meter (3.3 feet) high extend from the main dune field toward the rover. Scientists hope to send the rover down to one of these tendrils in an effort to learn more about the characteristics of the dunes. Dunes are a common feature across the surface of Mars, and knowledge gleaned from investigating the Endurance dunes close-up may apply to similar dunes elsewhere.

Before the rover heads down to the dunes, rover drivers must first establish whether the slippery slope that leads to them is firm enough to ensure a successful drive back out of the crater. Otherwise, such hazards might make the dune field a true sand trap.

Martian Spherules (also known as blueberries due to their blue hue in false-color images released by NASA) are the abundant spherical hematite inclusions discovered by the Mars rover Opportunity at Meridiani Planum on the planet Mars. They are found in situ embedded in a sulfate salt evaporitic matrix, and also loose on the surface.

The shapes by themselves do not reveal the particles’ origin with certainty. “A number of straightforward geological processes can yield round shapes,” said Dr. Hap McSween, an Opportunity science team member from the University of Tennessee, Knoxville. They include accretion under water, but apparent pores in the particles make alternative possibilities of meteorimpacts or volcanic eruptions more likely origins, he said.

Mosaic shows some spherules partly embedded, spread over the (smaller) soil grains.

For example, ranging in size from less than 100 micrometers to more than 250 micrometers, similar spherules were found in Moon soil samples collected by Apollo 12 at the Procellarum Basin, and Apollo 14 near Mare Imbrium (Sea of Rains), the dark crater that dominates the Moon’s face, and their properties were consistent with expectations for creation by meteor impacts.

“We see these strange round objects we’re calling “spherules” embedded in the outcrop, like blueberries in a muffin. The outcrop erodes away as it gets sandblasted, and the spherules (which seem to resist erosion better than the rest of the outcrop does) fall out and roll down the hill. Weird.” said Dr. Steve Squyres. The spheres may have formed when molten rock was sprayed into the air by a volcano or a meteor impact. Or, they may be concretions, or accumulated material, formed by minerals coming out of solution as water diffused through rock, he said in a February 9 press conference.

Not only are there spherules on the surface but they are also found deeper in the Martian soil. The difference between these and ones which were found at the surface was that they had a very shiny surface, that created strong glints and glares which made them appear shiny or polished. On March 2, Opportunity mission scientists reported that they concluded a survey of the distribution of spherules in the bedrock. They found that the spherules spread out evenly and randomly inside the rocks, and not in layers. This supports the notion that they grew in place, since if their origin was related to volcanic or meteoric episodes one would expect layers of spherules as a “record in time” for each event. This observation was added to the list of evidence for liquid water being present at this rock site, where it is thought the spherules formed.