Showing an overhead view of the valley as it cuts through the rim of Endeavour, Squyres described Perseverance as having “a braided sort of appearance” and “a very distinctive look that is the consequence of some kind of fluid flow.”

At the approximate halfway point on her journey however, Perseverance is still a real mystery. “We have multiple working hypotheses,” said Squyres. “When we started we had three hypotheses – dry avalanche, debris flow, some kind of fluvial river transport. We can test these hypotheses by looking at the features on the ground.”

Since last May, Opportunity and the team have been looking at all the features on the ground, as well as imaging the morphology. While they have found evidence that seemed to point to past water, they also uncovered other potential contributors to the original working hypotheses that would be detailed during the conference.

“Out on the plains above the top of Perseverance Valley, west of the crater rim, are some very broad shallow troughs that more or less seem to terminate at the top,” [the rim crest], “as if it they would be the kinds of things through which fluid flows, and then spilled down,” Squyres said, pointing to the top of the notch in another overhead image. “But there’s a serious challenge for this hypothesis. The top of Perseverance actually slopes up,” he said.“Mars is a weird place, but not so weird that water flows up hill.”

Still, it has been a few billions years or so, give or take. You could solve this if this surface was originally horizontal and then [part of] it went through some compaction –” he said. [Tim Parker, a MER Athena Science Team member and a geology lead, would expound on that as he offered up his lake spillover theory later in the afternoon.]

Once Opportunity got into the valley, the scientists found the topography to be “really very subtle,” Squyres said. “A lot of it is in-filled with soil.” The rover has also found plenty of visibly scoured outcrops.

At a site named La Bajada, where two distinctly different outcrops are separated by the valley path, the scientists even found breccia outcrop with telltale wind tails that “really caught our attention,” said Squyres, recalling how Opportunity popped two wheelies to be able to hunker down over this outcrop to and check it out up close. “This wind tail or flow tail indicates the direction of flow,” he said, pointing to an image of the flat rock at La Bajada. “And that direction is – uphill.”

Since wind blows radially out and up the crater rim, most of the science team members view this as “pretty strong evidence of wind erosion,” Squyres said. “This doesn’t mean the valley itself has been carved by wind, but it certainly at least points to aeolian erosion overprinting after the valley itself formed.” [Aeolian erosion was one of the multiple working hypotheses Rob Sullivan would focus on later in the afternoon.]