NASA’s rover Opportunity has returned an image of the Martian surface that is puzzling researchers.
Small spherical objects concentrated at an outcrop called Kirkwood on the western rim of Endeavour Crater differ in several ways from iron-rich spherules nicknamed ‘blueberries’ the Opportunity photographed in 2004.
“This is one of the most extraordinary pictures from the whole mission,” said Dr Steve Squyres of Cornell University in Ithaca, a principal investigator with the Opportunity team.
“Kirkwood is chock full of a dense accumulation of these small spherical objects. Of course, we immediately thought of the blueberries, but this is something different. We never have seen such a dense accumulation of spherules in a rock outcrop on Mars.”
The spheres measure as much as 3 mm in diameter. The analysis is still preliminary, but it indicates that these spheres do not have the high iron content of Martian blueberries.
The Martian blueberries found elsewhere by Opportunity are concretions formed by action of mineral-laden water inside rocks, evidence of a wet environment on early Mars. Concretions result when minerals precipitate out of water to become hard masses inside sedimentary rocks. Many of the Kirkwood spheres are broken and eroded by the wind. Where wind has partially etched them away, a concentric structure is evident.
Researchers checked the spheres’ composition by using an instrument called the Alpha Particle X-Ray Spectrometer on Opportunity’s arm.
“They seem to be crunchy on the outside, and softer in the middle,” Dr Squyres said. “They are different in concentration. They are different in structure. They are different in composition. They are different in distribution. So, we have a wonderful geological puzzle in front of us.”
“We have multiple working hypotheses, and we have no favorite hypothesis at this time. It’s going to take a while to work this out, so the thing to do now is keep an open mind and let the rocks do the talking.”
Just past Kirkwood lies another science target area for Opportunity. The location is an extensive pale-toned outcrop in an area of Cape York where observations from orbit have detected signs of clay minerals. That may be the rover’s next study site after Kirkwood.
“The rover is in very good health considering its 8-1/2 years of hard work on the surface of Mars,” said Dr John Callas of NASA’s Jet Propulsion Laboratory in Pasadena. “Energy production levels are comparable to what they were a full Martian year ago, and we are looking forward to productive spring and summer seasons of exploration.”