Pebbles May Be Mars Water Clues
Close-up pictures of the Martian surface taken by NASA’s Opportunity rover have revealed an unusual soil structure scattered with puzzlingly spherical pebbles, which may hold clues to whether water was widespread on the planet’s surface.
The pebbles are big, coarse, gray grains that may contain hematite, a mineral often formed in water that was one of the reasons the craft landed in Meridiani Planum in the first place, principal investigator Steve Squyres of Cornell University said Wednesday.
The grains are sitting on a material “that is very red, very fine-grained, that gets exposed in the bounce marks” left behind by the air bags that cushioned the rover’s landing, he said. “Then we’ve got this sand that looks like some kind of finely ground up basaltic sand.”
“What’s really intriguing are the ones that are so round,” said geologist Hap McSween of the University of Tennessee, a member of the science team. There are only a limited number of ways such spheres could be formed.
One way is at the bottom of a lake or ocean, when fine particles roll around on the bed, accumulating layers of material. Such spheres are called “ooliths.” If the spheres prove to be ooliths, that would be strong confirmation that large amounts of water once existed on the now-barren surface of Mars.
The team hopes to find some spheres that have been broken open. If they are ooliths, their interiors will show concentric layering.
The other possibility is that the spheres were small droplets of lava ejected from a volcano that froze into their round shape in the air.
Such “lapilli” could also have been formed when an asteroid strike ejected molten rock from a crater. If the spheres are lapilli, they will shed little light on the question of whether water was once on the surface.
Opportunity, which landed on Mars on Jan. 24, was scheduled to begin roving overnight, moving about 10 feet, halfway to a rock outcropping that is its next major destination.
After that move, it will stop for a couple of days and use its wheels to dig a trench on the Martian surface. Engineers will lock five of the rover’s wheels so they can’t move, then spin the sixth one to dig down into the soil just like a car stuck in mud digs itself deeper by spinning a wheel.
The process will probably take an hour or two because the wheel will be stopped frequently for picture taking. The rover will then back carefully away from the hole so that it can be examined with the instruments on its robotic arm.
Meanwhile, halfway around Mars, engineers were scheduled to spend Wednesday erasing all the data stored in the flash memory of Opportunity’s twin rover, Spirit.
They planned to reformat the memory in an effort to cure a computer malfunction that has plagued the craft for two weeks.
Spirit landed on Mars on Jan. 3 at Gusev Crater.
The team had hoped to resume scientific activities Monday by using Spirit’s arm to abrade the surface of the rock called Adirondack, but computer problems prevented the activity from being carried out.
The erasing and reformatting were to proceed very slowly to avoid making any irreversible errors, mission manager Mark Adler said. “We’ve spent four days testing the reformatting” at Pasadena’s Jet Propulsion Laboratory.
They hoped to have all the computer operations finished Wednesday so they could begin looking at Adirondack again this morning.
