Fellow BABBer and space dude Jim Oberg sent me a note about an Opportunity image showing a small crater. The crater is very small, though I cannot tell how big it really is. I suspect it's not even a meter across.

Here's a cropped image of it:



Craters in solid ground are usually big, because to make a crater at all you need a relatively big impactor to get through our air. The same is true for Mars, though the air is thinner so the impactor can be smaller. Still, this is really small! Now, when a smallish meteoroid comes in, it quickly loses velocity, and eventually slows to free-fall, and just drops in. If it hit a loose, sandy/dusty area it would leave a small crater like this one.

So I wonder if that's what this is. The crater is small, the surface looks dusty, and interestingly there is a shadowy pattern to the left which in my mind would match the pattern of sand/dust sprayed up from a slow impact and blown by the wind. Also note there is another crater behind it and to the left.

If true, then this may be Mars' youngest crater, and, even cooler, it won't be around for long! If it's just a pit made into sand, it'll blow away soon. Can anyone else look into this? I am short on time right now!

Some discussion here.

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It's not uncommon to see meteorites in pairs, even at very small scales. We saw several examples on Skylab (see figure 3-11 here http://history.nasa.gov/SP-404/ch3.htm )

Or maybe the Martians are shooting cannonballs at Oppy.

In this case, it's consistent with my scenario: a larger meteoroid broke up high in the atmosphere, and pieces plopped down next to each other. This happens all the time. I'd love to see more images, and closeups to see if there are smaller pits.

Shouldn't we be able to see the pieces that caused the craters at their center. Impact speed was low, so they should still be there. How old are the images? Is Opportunity still nearby and may be able to investigate?

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I talked to someone at JPL (to remain unnamed for now 8) ) who told me the craters are pretty small: the near one is 20 centimeters (8 inches)across! The farther one is only about 11 cm (4.5 inches) across. These are the smallest craters ever seen.

I was told that more images from this area are due in tonight, so stay tuned for more information. Keep checking the raw images for Sol 433 NAVCAM images.

yes indeed.

It is quite puzzling that there does not appear to be any remaining evidence of what created the diminutive crater.

Did it sink into the sand?

Could there be any connection with the iron meteorite Opportunity spotted two month ago?

But I guess, no. The ages must be very different.

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Depends on the distance. How far has Opp traveled since imaging that meteorite?

FYI, I just updated my blog with this item, and I also submitted it to Fark.

Brace for another site overload

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Several kilometers.

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Well, several kilometers may still put these in the "strewn field" of the fall. But this is mere speculation. I'll wait for the images tomorrow.

I cropped and brightness (+16), contrast (+16) enhanced the original image earlier today



If that crater in the foreground is only 8 inches (200mm) diameter then it looks to be no more than 12 inches (300mm) deep. With a sandy regolith the impactor could easily bury itself with only a modest (by meteoric standards) velocity, especially if it had a dense iron /nickle composition.

I do think we have to be carefull though. Erosional processes on Mars are slow and geologically recent events could be a few millenia old. That said, this pock mark does look very fresh - almost pristine. Has anyone a photos of bullet impacts in dry sand to use as a comparison?

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Could the craters be caused by pieces broken off of Opportunities heatshield or other parts during the landing?

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It reminds me of the small craters that kids can make in several hands-on exhibits at some of the cooler science museums I've visited in North America, (like the Denver Space Museum.) A motor in a glass case smooths out very fine sand, and then the kids (or adults like me) can mechanically lift and drop metal spheres from various distances and angles to make round craters that look exactly like those two on Mars.

The sand in the pictures is likely very fine powder or if not, maybe very loose?

regarding the "white bunny" and it's likely motion in the wind. What are the current average wind speeds in the area of Meridiani plains? I can see what appears to be an area of sprayed material to the left of the crater that appears to correspond neatly with the impact. Given the apparent looseness of the material, wouldn't the wind have pretty much erased this feature by now?

That being the case, surely that is likely to indicate a very young meteorite event.

Probably not - at this distance from the descent arc it would be a huge conincidence.

I must say and I both puzzled and perplexed by these craters. On the surface these look just like the small craters you would expect from micrometeroites striking the surface. However, there are lots of problems with this.

For starters, I am under the impression (no direct reference to quote unfortunately) that the atmosphere on Mars, while thin is both dense enough and deep enough to shield the surface against such micrometeorites. Which is why the surface does not look sand blasted in the lander images, unlike the lunar surface. Even if they are micrometeorite craters, given such craters are very rare on Mars - these are the first seen by any rover or lander - it seems unbelievably improbable that two such craters should occur within metres of each other, both looking equally fresh.

However, the alternatives seem even more unlikely. The location is wrong for something coming of the lander during the descent and finding them would be again most improbable.

Gases from the interior of Mars might make surface pockmarks, but surely not in surface sediments as porous as these. And if there were gases seeking to the surface, why not more?

I am just waiting for some woo woo to say that this is evidence for giant ant lions or something.....

Jon

When I was a kid, we called them sand devils but google shows your term to be the far and away leader. Ant lions it is. Those things are so cool, nothing I liked more than tossing a few ants in those pits. This was, of course, before video games and the interweb. Good times.

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Building on the reasoning by Jon I would like to suggest that these are secondary craters. This also makes it slightly more likely that the primary impact was the MER heatshield. With very low air resistance and low Mars gravity I think small pieces of debris could travel surprising distances after the primary impact. Of course, the same goes for natural impacts.

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I've been trying to build up a simple model for this ever since Oppy came across the HeatShield iron meteoritr. My amateurishness is really frustrating me at this stage however the numbers that I have indicate that the martian atmosphere, thin as it is (~12g/m^3), is still very effective as a shield. As far as drag is concerned it will slow most things under half a meter in diameter down to ~1000-1500 m/sec terminal velocity. That's still pretty fast but it's a lot slower than the 7km/sec that seems to be the expected average for objects hitting mars. The other part of my current calculations indicate that anything under ~7m diameter will generate more heat energy during the deceleration than is required to atomize the meteor (assuming it's pure iron for simplicity).

My model is too simple though (I'm assuming no variation in atmospheric density yet for example) and in reality things would break up under these sort of conditions with small pieces making it to the surface but the basic conclusion I'm drawn to is that even fairly large meteors will still mostly burn up. Heatshield rock obviously makes a nonsense of my calculations unless it is a fragment of something much bigger.

Are there any real experts in this field lurking about who can comment?

The inner portion of the foreground crater looks smooth (even in the unenhanced image). Is that an indication the impacting object was hot? BA has already said it might have been slowed significantly by its interaction with the atmosphere, but that doesn't mean it was cold at the time of impact. Is martian sand of similar composition to terran sand (i.e. silicates)? Could a hot meteorite have fused some of it? That could slow erosion.

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More images: http://marsrovers.jpl.nasa.gov/galle...nity_p436.html

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The Pancam composition of the filters L456 shows somewhat more details:

http://www.greuti.ch/oppy/pan-oppy-sol436.jpg

Nice image! Doesn't seem to show any evidence of fusion, looks as if whatever caused it just plopped into free dry sand.

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The better the pictures, the more it looks like an ant lion!

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Reminds me of "Enemy Mine"...
But those were bigger...

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Is there another one farther away on the crest of the dune? Almost on a line with the two nearer ones in this image.

http://marsrovers.jpl.nasa.gov/galle...3P1893R0M1.JPG

Cannon balls are trying to get the range?

Opportunity Discovers Tiny Craters on Mars

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