If it is in fact from a crater, visiting something that fresh would be amazing for science return: seeing what else was excavated, maybe even the original meteorite itself if it was a small impact (say Heat Shield Rock sized)
Of course, even if Hirise/CTX spot something new we shouldn't get our hopes up to visit it right away. They'll probably have to wait for winter to end to actually be able to access it (and finish the science campaign right here at Solander).

Exactly. As Walfy's animation shows, the idea is not that the slow movement of the wheel while steering acted like a golf club or putter to shoot the rock out. Of course that could not happen. The idea is that the rock was stuck in place, which would not be surprizing. As the steering wheels turn against the rock, the force builds until the rock's connection to the ground snaps. Suddenly it's free and you'd expect it to move out faster than the speed of the steering wheels. And there would have been two steering steps, at the start and end of the turn - is it clear that neither could've snapped the rock out in the right direction? Perhaps it ricocheted off another wheel?

About ejecta, we need actual numbers to say anything definite about how likely a nearby hit is. But this is what makes me extremely sceptical: We've seen several meteors within pancam-shot of Oppy, but no evidence of recent hits (last 10 years, say) of meteors or ejecta. So what are the odds that when we do see a fresh piece of ejecta, it hit within a couple of metres of Oppy? Surely it would've been far more likely to hit a few years ago, say, and then we drove up to it. It's the close link with Oppy and the timing that strongly suggests a connection with the bump on 3540.

Probably what marsophile pointed out above:
http://marsrovers.nasa.gov/gallery/all/1/p...EOP2596R1M1.JPG
That's on the left-rear side of the rover.

Doug, you may know this: Is someone actually compiling MRO data to derive an impact probability for a given location on Mars within so-and-so many meters or km over a fixed timespan? If so, I'd guess that they're still acquiring data to firm up the model.

I agree with Fred in any case; odds are overwhelmingly in favor of this being an uprooted rock that was transported for a bit.

It's intriguing though that it has a 'very unusual composition'. Does that mean that all the rock at this spot is 'very unusual' or that this particular rock is atypical of its surroundings? In the latter case we are twice fortunate that an unlikely case of wheel tiddlywinks happened to turn up a very unusual rock.

Personally I think everything points to this special rock being spring-loaded. It was primed to leap in the air as soon as anybody touched it.

That is the most logical explanation to date Fred and Walfy. As previously mentioned this rock looks like it separated along a fracture which would permit the build up of force until the (hydrothermally derived) material deposited within the fracture gave way, providing a reasonably significant kick off velocity. This scenario would I think provide the necessary accumulation of force and instantaneous release, whereas a loose rock, even in duricrust would provide much less resistance and a more gradual release. I am not sure that the actual turning of a wheel would accumulate the necessary force and I would assume that there would be some feedback based control to preclude the wheel turning against significant resistance? I would therefore tend to punt for the RF 'frozen' wheel being the prime suspect as during a turn, for some encounter orientations, it would push against an obstacle rather than over-ride it and the inertia of the rover in the turn would provide a significant force.

Already done, put to paper, peer reviewed and published
http://www.sciencedirect.com/science/artic...019103513001693


Walfy's animation seemed to me to suggest it was just a steering actuator bashing something out the way - which I hope we all agree is just not going to happen.

The notion that rover motion (of any sort) could end up 'popping' a rock into motion is fine. This all falls under the tiddlywinks category, surely? It's really not a separate means of flinging material

Huh. Didn't know they'd found so many thus far. Thanks!

A few possible scenarios:

1. One rock acting as a lever, one rock acting as a fulcrum, the rover weight on the lever.

2. Rover starts passing over a slab with a hollow underneath. When the rover is halfway the rock breaks under the weight of the rover. The part that is not under the rover gets flung into the air by the force of the so-called normal reaction to the weight of the rover. (This is similar to Fredk's suggestion except it is the weight of the rover rather than the forward momentum that snaps and throws the rock.)

3. Ngunn's suggestion about spring-loading. The rock may have been under stress to begin with and Oppy's turn was the "straw that broke the camel's back."

4. The soil under the hard crust may be under pressure in places, or perhaps sparks or heat from the pressure of the rover weight reacted with some volatile.

More interesting than the origin may be what the rock can tell us about the subsurface. Perhaps we should try to duplicate the event that produced the rock in other likely places.

I'd have to say that walfy's suggestion sounds the most plausible to me. A rock propelled by stored-up energy from the rover's suspension/frame/wheels system during a turn just seems most likely to me; especially considering that we can see a similarly sized, disturbed area quite nearby, and aligned with the projected path of Oppy's wheel tracks.

Regarding the curious composition of P.I, we really don't know whether or not that is anamolous in this locality. Furthermore, we rarely, if ever, have seen Opportunity analyze the bottom side of a flipped-over piece of rock. Who knows which salts might have accumulated in that environment?

It's been a while since we've had a bonafide Martian mystery like this to unravel. Good work, everyone. This is fun.

Some post-brush Pancam images of Cape Elizabeth came down. The post-brush color of Cape Elizabeth looks a lot like the interior color of Pinnacle Island to me. Here's the L257:

I notice the dust factor has been steadily improving over the last several status reports.

The rover has been tilted during this period. I wonder if the simple fact of being tilted could affect the deposition/removal "budget" so that a small net deposition could be transformed to a small net removal. Presumably the deposition comes mostly from the vertical fall of dust so a tilted rover might present a smaller collection area. On the other hand, the wind might be primarily horizontal so a tilt might help there.

IMHO, I can't visualize a tiddlywink or leveraged snap-effect scenario really having enough rebound to push a rock more than a few cm, and though I might be completely wrong, this rock seems so crumbly its hard to see much stress building up.

While still somewhat far-fetched, though still seems most feasible to me (and I still don't know if the wheel configuration and maneuvers support it, because it requires the wheel to be upslope for the 'catch' and downslope for the 'release'), is the wheel abutting against the PI source and dislodging it so that it becomes deposited inside the interior of the wheel.
At this point when the wheel turns, since PI would lie flat as a sort of hemi-square wheel shape, it should, as the wheel turns slowly, usually become rotated to a near vertical orientation inside the wheel and so as the angle of lean transfers to the tip-over point, it could either be re-deposited back inside the wheel for another rotation, or if its on the edge of the wheel in the right configuration, can escape in that vertical orientation, and may accumulate some extra height if it hangs on long enough.
So then if the part of PI that then contacts the ground is not the square half, but is the roundish half, and the ground has enough slope to it (a 15 degree slope isn't quite trivial), PI may gain enough speed from that small drop to roll several revolutions until the square sections stall it to flop over into its current location.

The main problem with propelling PI is converting the very slow rover and wheel movement into rapid PI movement, and what you're saying about the rock inside the wheel hitting the "tipping point" as the wheel rotates sounds like it would do that. Getting PI out of the wheel sounds trickier. The wheel being on a slope might help - with the right tilt, PI would move outwards as well as downwards once it started to slide inside the wheel. You could use basic physics to work out PI's maximum speed as it left the wheel. Friction would make it slower though.

It would help to know exactly where PI came from and how far that is from it's current location. We have a candidate "divot" - it shouldn't be too hard to estimate the distance from there to it's current location. Of course turning in place and driving can do multiple damage to the ground, so the visible divot may be unrelated to PI, and the real source may be underneath us and invisible, at least until we move again.

http://marsrovers.jpl.nasa.gov/gallery/all...EOP1311L0M1.JPG

The "divot" and some of the area around it is visible in the rear hazcam from Sol 3540.



A closeup (but fisheye-distorted). Compare with

http://qt.exploratorium.edu/mars/opportuni...EOP2599R1M1.JPG