The western route, 5th leg after stop at Absecon / Reeds Bay Options

[Tesheiner]

Time for a new thread.
After moving southwards for ages, the "detour" by the western path has started with a 60+ meters drive on sol 1942.


There are no images yet --they should be available on the next update-- so this image was calculated solely based on the rover's mobility info. I'll update the route map later.

[Juramike]

Here are two MI images of Vail Beach, the gravelly area in front of Block Island, taken way back on Sol 1974:
http://marsrover.nasa.gov/gallery/all/1/m/...XP2956M2M1.HTML
http://marsrover.nasa.gov/gallery/all/1/m/...XP2956M2M1.HTML

Some heavily pitted materials can be seen in the second image (Block Island fragments?)

All this begs the question: Why is Vail Beach here? Are these the result of a small long gone crater that sat well above this layer and ablated away?

Here’s a possible scenario:

Block Island meteorite smacks into sediments and forms a crater on a plain well above the current level. As the surrounding deposits and the crater ablates away, more resistant rock and pebbles and blueberries roll and concentrate into the crater bottom. Eventually the Aeolian erosion level reaches the crater bottom and the loose friable deposits ablate away, slowly lowering the concentrated pebble fragments onto the current level we observe today. The pebbles form a nice armor, and prevent dune formation directly in front of Block Island. Behind Block Island, the lower windspeed causes sand deposition. (Just Immediately behind Block Island, there is a small patch of brighter dust visible in Stu’s images.)

This would make Vail Beach the remnants of a fossil “internal mold” of a long gone crater formed when Block Island smacked into Meridiani...


(This is following a train of thought that Fran Ontanaya started here.)

[MarsIsImportant]

Here are two MI images of Vail Beach, the gravelly area in front of Block Island, taken way back on Sol 1974:
http://marsrover.nasa.gov/gallery/all/1/m/...XP2956M2M1.HTML
http://marsrover.nasa.gov/gallery/all/1/m/...XP2956M2M1.HTML

Some heavily pitted materials can be seen in the second image (Block Island fragments?)

All this begs the question: Why is Vail Beach here? Are these the result of a small long gone crater that sat well above this layer and ablated away?

Here’s a possible scenario:

Block Island meteorite smacks into sediments and forms a crater on a plain well above the current level. As the surrounding deposits and the crater ablates away, more resistant rock and pebbles and blueberries roll and concentrate into the crater bottom. Eventually the Aeolian erosion level reaches the crater bottom and the loose friable deposits ablate away, slowly lowering the concentrated pebble fragments onto the current level we observe today. The pebbles form a nice armor, and prevent dune formation directly in front of Block Island. Behind Block Island, the lower windspeed causes sand deposition. (Just Immediately behind Block Island, there is a small patch of brighter dust visible in Stu’s images.)

This would make Vail Beach the remnants of a fossil “internal mold” of a long gone crater formed when Block Island smacked into Meridiani...


(This is following a train of thought that Fran Ontanaya started here.)

I see one major problem with this line of thought. Let's take a look at the bigger picture. Why are all the iron meteorites exactly on the surface, not just this one?

If there was surface excavation along with ablation through wind erosion, then the chances that these would all be on the surface would be next to zero. At least some of these big meteorites should be at least partially embedded into the ground.

But if the former surface that is now gone used to be ice, then everything makes sense. The meteorites would eventually all sink down to the same level were there was no more sublimating ice. Everything would appear to be gently laid down on top of the surface - because basically it was.

Do we have any examples of iron meteorites at Meridiani embedded into the ground where only part of it can be seen?

[Juramike]

If there was surface excavation along with ablation through wind erosion, then the chances that these would all be on the surface would be next to zero. At least some of these big meteorites should be at least partially embedded into the ground.

This is probably giving us an idea of rate of "resistant" impacts vs. ablation erosion rate.

Imagine a surface dotted with craters of varying depth. Some containing resistant meteorites.

If the cratering rate (of resistant impactors) was really high, and the erosion rate really high: then we should see exposed meteorites all over the place. There would be a few still partially buried, but those would get completely exposed in the blink of an eye. (Once exposed, they remain exposed. The time it would take to exhume would be the time it took for the surrounding sediments to be removed along the Z coordinate of the embedded meteorite.)

If the cratering rate (of resistant impactors) was really low, and the erosion rate really high: then we should see a few exposed meteorites lying around completely exhumed, only a few would be buried (but not for long).

If the cratering rate was high, and the erosion rate really low: then we would see only a few popping out of the surface. Most would still be buried (and they'd stay that way for a while)

If the cratering rate was low and the erosion rate low, then the few resistant impactors would be buried.

We've got an n=3 of exposed meteorites that we've seen in our journeys. Is this a "few" or "a lot" or "all over the place"?
The unknowns are still the resistant meteorite cratering rate and average emplacement depths (most of the meteorites are within a few orders of magnitude in size), the absolute time-averaged erosion rate, the absolute age of the current surface, and the absolute age of the highest layer in the historical stack.

At least we can safely say that the resistant-impactor cratering rate is significantly above "never".