[X] My Assistant

[jaredGalen]

Looks like the streak spotted back in March is most likely a bit of a comet called Wiseman–Skiff. According to this article

Fantastic little addition to Spirits 'research portfolio.'

[abalone]

Did someone already noticed/discussed this image, taken by Opportunity on Sol 300?
Even though could be a cosmic ray hit, trail strongly resamble to a bolid photographed in full day sky (so a very lumonous one!)...

Looks like a candidate to me, surprised that noone has mentioned it before. Well done for spotting it
Richard

[Bob Shaw]

So: Some 'minor' (10KPS!) velocity differences between Earth and Mars impacting objects, no effective oxidation, some intense heating but also rather *little* heating in some cases. Presumably, strange shock effects here and there, too.

But: (and this is a big one) There *is* a huge difference between the dynamics of an object zooming through the upper atmosphere of the Earth and one heading for Mars. And it's this: the Martian atmosphere is thinner than ours, and goes out a bit further, and so on (but in many ways would behave like our own at a very high altitude) but it *doesn't* have a 1Bar surface pressure. Objects won't hurtle in then shatter on the 'hard' lower atmosphere, then drift to a halt on the surface. Instead, they'll keep going and I'd wager that their terminal velocities are *not* as on Earth! Volume (and mass) rise as the cube of the diameter, while surface area goes up only by the square, so small objects should be far less effectively slowed on Mars. We're talking about small objects hitting HARD.

I suppose the buckshot effect on some rocks *might* be impact created, then...

...(eating words previously uttered!).


Of course, there's the Heat Shield meteorite to consider...

[helvick]

So:  Some 'minor' (10KPS!) velocity differences between Earth and Mars impacting objects, no effective oxidation, some intense heating but also rather *little* heating in some cases. Presumably, strange shock effects here and there, too.

It's a significant difference but 50kps is an outrageously fast speed nonetheless. At atmospheric entry speeds the surface of the object and the molecules in the atmosphere are atomized to plasma. Then there is all of the complex shock wave hypersonic stuff.

I don't think the differences are as significant as you think. At the altitude that most meteors vaporize on earth (90-100km) the martian atmosphere is thicker due to the lower gravity and on Mars there is more atmosphere above that altitude than on Earth. The shattering\disintegration effect you describe does not happen because the objects hit a 1 bar (or a 0.1, or 0.01 bar) plateau it starts to happen right at the edge of the atmosphere.

You are spot on about terminal velocities - they are much higher on Mars - the lower gravity slows things down a bit but the 0.01 bar ground level atmospheric density is what counts. A 10cm iron rough sphere has a Vt of ~700m/sec on Mars, ~100m/sec on Earth and for fun ~30m/sec on Titan.

Of course, there's the Heat Shield meteorite to consider...

While I still maintain that the "average" meteoride will vaporize unless it's very massive on Mars or Earth there clearly are objects that aren't average.

The points made by dvandorn and abalone about meteorites found on earth are true - these things regularly hit the surface even on earth. The outer atmosphere gets pummelled by the perseids, leonids, taurids and countless other showers of debris but to the best of my knowledge none of those actually makes it to the ground. The stuff that does has to be significantly different from the average in some way, certainly by having an orbit that results in an impact well below the 50-60km/sec that results from the "normal" impact from a retrograde object.

This Arecibo Meteor Velocity Study shows that around 5% come in at around <10km/sec. Those could survive and many probably do.

So if there is a small but not insignificant percentage that should survive then if the Martian surface is extremely old shouldn't the entire surface be blanketed with meteoric debris or dust\debris that has a significant component that is of meteoric origin?

[Bob Shaw]

All very true - but I still think that the population of 'landers' will differ from the Earth. The fast chaps are one thing, but the other guys...?

I've said to as many people as I could for as long as I could that the moon should be an interesting place to look for meteorites, but with the Mars meteorites on Earth and the Antarctic experience in particular I'm beginning to wonder whether Mars - with it's putative long-term mobile ice features and aggressive sublimation - might actually be a perfect environment to look for the remnants of early planetary (plural) surfaces? Consider: we might have analogous situations to Antarctica (Allen Hills etc, blue ice) on Mars which might preseve not only proto-Mars but also rocks from earth, or Venus!

This whole area deserves a l-o-t of thought - imagine a sample return mission which could obtain material from several planets at once...

[abalone]

I've said to as many people as I could for as long as I could that the moon should be an interesting place to look for meteorites,

The problem with the moon is that most of the meteor(ites) really do vaporise on impact. That why the moons regolith is full of glass beads. What does not vaporise is shattered and mixed with the results of previous impacts.

A place like Merridian is ideal. It seems to act a little like the Antarctic in the the underlying bedrock is so unlike any meteorite in composition the they would be unmistakeable, and the surface is slowly being eroded just like the sublimation of the Anarctic ice. Those small shifting sand dunes must be full of them, on lots of occasions small rocks have been visble between dune crest and I suggest that many of these are meteorites. They have imaged some of them from a distance but not taken the time to investigate. The two rocks outside craters that they did investigate, one right at the beginning called Bounce seems to come from another area on Mars and the other Heat Shield Rock was a meteorite.

So why not spend more time on these, well we already have tousands of them on Earth and only about a dozen Mars meteorite. It is probably a poor use of resources to use the rovers for this.
Richard

[edstrick]

If, big-if, the bright colored etched terrain materials are exposures of Meridiani sulfate rock between thinner and/or sparser drifts of basalt and dune materials...

We may see a lot more of random rocks from the sky scattered across the terrain on top of the Meridiani sulfate rock layers than we can see in the scattered thin inter-drift deposits we've been crawling over. Maybe.

[Bob Shaw]

I don't think I'd suggest using valuable rover resources to go meteorite-hunting at present, but as a future goal, that's another matter! Anywhere that sorting of debris has happened seem like places to look - the polar deposits (ice and CO2), polar moraines, talus below water seeps, polygons, sublimed-away ice features... ...loads of opportunities, if we have the spirit! (sorry)

Whether or not rovers would be up to the job - ever - is something that we might question - it may be a case of the Mark I Human Eyeball being needed, not to mention them gripper manipilatory things, what do you call 'em, oh yes - hands!

[helvick]

This whole area deserves a l-o-t of thought - imagine a sample return mission which could obtain material from several planets at once...

Not a bad idea at all. As Abalone says places like Meridiani should act somewhat like Antarctica but on a significantly longer timescale so there should be lots of non martian debris mixed with the local stuff.

Slightly OT warning: While searching for data on this I found an amazingly balanced review of research on meteor rates by some folks at the Institute of Creation Research of all places. Moon Dust and the Age of the Solar System. It's very long and in depth, full of good reference material and comes to (what seem to me) sensible conclusions despite the fact that the authors clearly wished otherwise. It would be useful if more creationist research were this thorough.