Sep. 14, 2012 at 9:23 PM ET
Eight years ago, NASA's Opportunity rover came across strange-looking spheres that were nicknamed Martian blueberries — and now the Mars rover has sent back a picture showing a different flavor of berry that has the experts scratching their heads.
"This is one of the most extraordinary pictures from the whole mission," Cornell astronomer Steve Squyres, the rover mission's principal investigator, said today in a news release.
The golf-cart-sized Opportunity rover used the microscopic imager on the end of its robotic arm to take a super-close look at the spherical shapes. These particular berries, measuring as much as one-eighth of an inch (3 millimeters) in diameter, cover an outcrop called Kirkwood in the Cape York segment of Endeavour Crater's western rim.
"Kirkwood is chock full of a dense accumulation of these small spherical objects," Squyres said. "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."
Iron-rich Martian blueberries first came to light soon after Opportunity headed out from its landing site on Mars' Meridiani Planum in early 2004. The fact that they have layers of a mineral called hematite suggests that the spherules were formed by the action of mineral-laden water percolating through rocks. That's how similar spherules formed on Earth, where they're known as thunderballs, shaman stones or Moqui marbles.
Since then, Oppy has run across the blueberries (which are actually gray) many times. A couple of years ago, the rover spotted an unusual spread of blueberries that were so tightly packed that scientists called it a "blueberry sandwich."
Some scientists say the berries could become important in the search for signs of life on Mars: In the August issue of the journal Geology, researchers from the University of Nebraska and the University of Western Australia contend that microbial activity played a part in the formation of iron spherules on Earth — and may have played a similar role on the Red Planet. Spherules with an iron-rich exterior and an iron-poor core could "offer a macroscopic target in the search for life on Earth as well as Mars," they wrote.
Crunchy on the outside, soft on the inside
Last week's discovery adds a new twist to the berry investigation. Many of the spheres on the Kirkwood outcrop have been broken open and eroded by the wind, NASA said. The eroded berries show signs of a concentric structure. To investigate further, Opportunity aimed its Alpha Particle X-Ray Spectrometer at the berries and analyzed their elemental composition. The preliminary analysis indicates that the recently found spheres do not have the high iron content seen in the original Martian blueberries.
"They seem to be crunchy on the outside, and softer in the middle," 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."
There's plenty to investigate around the place where Opportunity is now: Just past Kirkwood, there's an intriguing pale-toned outcrop in an area where orbital observations have suggested clay minerals are present. That's another sign that the region's geology was influenced by the presence of water in ancient times.
It's been eight and a half years since Opportunity dropped onto the Martian surface, cushioned by a layer of bouncy airbags. Opportunity and its twin on the other side of the planet, Spirit, were expected to last at least three months. Both of those rovers became overachievers. Spirit finally gave up the ghost just a couple of years ago, but Opportunity is still going strong at 14-mile-wide (22-kilometer-wide) Endeavour Crater. This week, the team behind Spirit and Endeavour received the prestigious Haley Space Flight Award for pioneering "new techniques in extraterrestrial robotic system operations."
After weathering another Martian winter, Opportunity is raring to go.
"The rover is in very good health considering its eight and a half years of hard work on the surface of Mars," John Callas, project manager for the rover mission at NASA's Jet Propulsion Laboratory, said in today's news release. "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."
Curiosity on the move
Meanwhile, thousands of miles away, NASA's Curiosity rover is on the move after completing the checkouts on its robotic arm. Curiosity, which arrived on Mars a little more than a month ago, is about twice the size of Opportunity — and thanks to its nuclear power source, it could theoretically last for decades.
The rover is heading for its first major destination: a geologically interesting spot called Glenelg, roughly a quarter-mile (400 meters) away from its landing site in Gale Crater. NASA reported today that Curiosity "perambulated over 105 feet (32 meters) of unpaved Gale Crater" over the past Martian day, or sol. It has put 466 feet (142 meters) on its odometer, and is roughly a quarter of the way to Glenelg.
This week, Curiosity turned its Mastcam imaging system toward the sun, to watch the Martian moon Phobos pass over the solar disk during the Red Planet's equivalent of a partial solar eclipse. Hundreds of thumbnail images were sent back to Earth, but the resolution wasn't sharp enough to show the eclipse. We'll have to wait until the full-resolution images are transmitted to gauge the success of Curiosity's eclipse-watching session. The timing of that transmission is dependent on where it's placed on the mission team's data priority list.
There'll be at least a couple of additional opportunities for eclipse-watching from Mars over the next few days. "This occurrence of transits happens twice per Martian year, which is once every Earth year," deputy project scientist Joy Crisp said during a teleconference on Wednesday, "so we did really want to scramble this time to try to take images."
The transit observations are something of a sideshow for Curiosity's $2.5 billion, two-year primary mission. The rover's main objective is to study Martian soil and rock for the chemical signatures of potential habitability. After spending a few weeks at Glenelg, the rover is due to begin a 12-mile (20-kilometer) odyssey to reach the flanks of a 3-mile-high (5-kilometer-high) mountain in the middle of Gale Crater, known as Aeolis Mons or Mount Sharp. The layers of rock on that mountainside could preserve the biggest geological record ever studied on Mars, going back billions of years — and provide new pointers in the search for traces of life on Mars.
Where in the Cosmos
Opportunity's new flavor of Martian berries served as today's "Where in the Cosmos" photo puzzle on the Cosmic Log Facebook page. It took just seconds for Allen Gregory and Richard Braastad to tell me that the picture came from Mars, and Robert R. Reilly got the blueberry connection. To reward their quick wits and typing fingers, I'm mailing out 3-D glasses, courtesy of Microsoft Research's WorldWide Telescope project. They'll come in handy for checking out 3-D pictures of Curiosity's trek. Ready for another puzzler? Click the "like" button for the Cosmic Log Facebook page, and get ready for next Friday's "Where in the Cosmos" picture.
Update for 12:30 a.m. ET Sept. 15: After some justified goading from one of my friends on Twitter, I emailed Steve Squyres a follow-up question: "If the spherules at Kirkwood are not as iron-rich as typical blueberries, what is their composition?" Squyres was kind enough to write back almost immediately:
"We're still working on that. At this point it's easier to say what they aren't than what they are.
"The spherules are much smaller than the APXS field of view, so we can't isolate a single spherule and measure its composition. Instead, what we measure is a field of view that has two different components in it. The field of view is partly filled with lots of spherules, and partly filled with the stuff they're embedded in, which we call the matrix.
"These two materials, when mixed together like that, have a composition that's a bit like 'average Mars' ... there's nothing noteworthy about it. That's why we're confident in saying that the spherules are not notably rich in iron, and the matrix is not notably rich in sulfur. If they were, we'd see it in the data. With just one measurement, though, we can't disentangle the compositions of the two different materials from one another.
"There's a solution, though. If we can make several measurements, with differing fractions of the field of view filled by spherules in each one, we can do some math and separate out the composition of the two components. And at that point, we'll get a good handle on what the spherules are made of (and, of course, also the matrix).
"It's an interesting mystery... and one that'll take a little while longer to solve."
More about Mars:
Alan Boyle is NBCNews.com's science editor. Connect with the Cosmic Log community by "liking" the log's Facebook page, following @b0yle on Twitter and adding the Cosmic Log page to your Google+ presence. To keep up with Cosmic Log as well as NBCNews.com's other stories about science and space, sign up for the Tech & Science newsletter, delivered to your email in-box every weekday. You can also check out "The Case for Pluto," my book about the dwarf planet and the search for new worlds.