Mars rover Opportunity has got itself stuck in a sand trap, while its twin, Spirit, has been gazing at the debris of ancient volcanic eruptions that took place when Mars was a distinctly wetter planet than it is today.
NASA scientists say that the Spirit rover has found some really interesting geology. It spent the last couple of months climbing up "Husband's Hill", the tallest in the Columbia Hills range in the Gusev Crater.
Although the rover has been close enough to the ground to take interesting samples, and send back close-up images, it was hard to get a sense of the overall picture, NASA scientists say, particularly because the layering of the rocks closely matched the slope of the hill Spirit was climbing.
However, now that Spirit has turned around an is looking back on its progress, the whole picture is starting to fall into place. "Looking back downhill, you can see the layering, and it suddenly starts to makes sense," said NASA's principal investigator, Dr. Steven Squyres.
Spirit's examination of rocks has revealed that some contain the mineral Ilmenite, a titanium-iron oxide formed during the crystallisation of magma. It also found that the textures of the rocks vary greatly at different layers - some areas have very fine details visible only to Spirit's microscopic imager. Others are clumpy, like grains all stuck together. Still others are massive rocks, with very little fine detail.
"Our best hypothesis is we're looking at a stack of ash or debris that was explosively erupted from volcanoes and settled down in different ways," Squyres said.
"We can't fully rule out the possibility the debris was generated in impact explosions instead of volcanic ones. But we can say, once upon a time, [the Gusev Crater] was a pretty violent place. Big, explosive events were happening, and there was a lot of water around," he went on.
Opportunity, meanwhile, has been stuck in a ripple-shaped sand dune for a little over three weeks, NASA says. The rover has managed to dig its way forward just 11 inches in that time. If it had been trundling freely across the planet's surface, it would have travelled around 157 feet.
If it does manage to get itself free, it will be put to work examining the ripple to try to find out why it was such a problem. The rover has traversed several other ripples in the windblown Meridiani plains, and NASA researchers are curious as to why this one has it stumped.
You can see Spirit's view back down Husband Hill here. ®