Festoon Cross-Bedding

Opportunity has found more festoon cross-bedding in the ancient bedrock of Erebus crater. While it has been seen before in Meridiani, and one of the key pieces of evidence found by Opportunity of past liquid water at that location, this new find is considered by the Mars rover team to be the best example so far.

Another good update from Steve Squyres himself here:

"Over at Meridiani we're still at the Olympia outcrop, but we have come to realize that our extended stay here has yielded a very important find. We've spent a lot of time recently taking high-resolution Pancam images of the rocks around us at a range of lighting angles, to bring out fine details in the layering. And if you look at one of the Pancam images that came down on Sol 690, you'll see that we have now found the best example of small scale "festoon cross-bedding" that we've seen the whole mission.

When you're talking about layering in rock, "festoon" geometry means little nested concave-upward shapes. They look like little smiles a few centimeters across. This kind of layering is seen in sedimentary rocks on Earth, and when it's found at small scales like this it provides solid evidence for deposition in flowing liquid water. It was small-scale festoon cross bedding that led us to conclude that liquid water had been present not just below the surface at Meridiani, but occasionally at the surface as well. If you're interested in the gory scientific details, check out the paper by Grotzinger et al. that we recently published in Earth and Planetary Science Letters.

We've seen small-scale festoon cross-bedding before, of course, at Eagle Crater and again at Endurance Crater, but this is by far the best example that we've seen yet. Once we've got Opportunity moving again, our first task is going to be to drive over to this spot and take a big Microscopic Imager mosaic on it, to document the cross-bedding in detail."

Image credit: NASA/JPL