Mars Rover Finds Rock Resembling Meteorites That Fell to Earth

What next? Mars rover finds rock that looks just like a man's thingy?

If you want to do something useful with your 'oh so blooming wonderful' Mars rover, why not drive over to where our much humbler British effort is languishing and give the bloody thing a kick.

It'd be nice if they rovers COULD do that, unfortunately with the limited lifespan of these rovers, I doubt they could make it out to whereever beagle 2 might have hit. Never mind that it's likely beagle 2 crashed into the surface of the planet at high velocity, and that it's likely theres not much left to be fixed/examined/"kicked".

Just because you're unhappy that the US Rovers survived, and the british rover didn't, is no reas> What next? Mars rover finds rock that looks just like a man's thingy? >

Do I see sour grapes? Gee dude, we all lose probes. God knows the U.S. has lost its share. Get over it. Your next one will be that much better. Perhaps it will land without cracking up. Whether it works afterwards is anyone's guess.

Yeah, and how many astronauts died on Beagle 2? We lost seven just a year ago. And he has the nerve to rant?

Only Astronomers and their astrologer friends lose probes. The rest us simply lose time, working around NASA to crap to see if the French got any rockets that work.

Whatever you say, ZZ.

Of course you do, it was a real disappointment when it disappeared. Did I ever claim superhuman qualities?

Uh? Lost me there, what has that got to do with it?

It was not actually a serious request for assistance. Personally I am intrigued by the revelations emerging from the red planet, but why do I have to read them on comp.robotics.misc?

Whatever. You will probably continue to cross post across the groups, I probably won't continue to rant.

Even if the rocks have similar spectra, I'm still puzzled by the rarity of rocks on Mars matching the Martian meteorites. A couple possibilities:

(1) We've seen very little of the Martian surface, and what we have seen has been selected for ease of landing. The rocks we're looking for are abundant on most other parts of Mars.

(2) There are lots of Martian meteorites on Earth, but only this one class has been identified; the rest are indistinguishable from "ordinary" meteorites (and presumably have lost any Martian gas that was trapped in them).

(3) The putative Martian aren't Martian.

OK, that was three possibilities. Comments?

Mike McSwell

Well, yeah, I have a couple. Actually, we have photographed nearly all if not all of the Martian surface, so to say that we've only seen a little is really an over-simplification. Secondly, What we have seen indicates that Mars has quite a diverse range of rock types, compared to the moon, for instance, and many other bodies in our solar system, with the exception of the earth. So it doesn't surprise me at all that it has taken so long to come up with a match with Martian meteorites found on earth. The fact that they found a rock on Mars that so closely matches one found on Earth is really astonishing, in my view. Finally, number of meteorites that have been found that didn't originate from Mars vastly outnumber the number of meteorites that did. There really aren't as many Mars meteorites as your might think. The chances that they would have matched up these two rocks is likely to be much lower than finding the proverbial needle in a haystack.

Don't forget that the meteorites are all relatively recent arrivals, simply because recently-arrived meteorites are the ones that are recognizable as meteorites. They may well be derived from only one or two major impacts on Mars, i.e. from the rocks at one or two points on Mars. So it is not too surprising if they're not typical of the surface; we're seeing a very small and not necessarily representative sample.

Remember also that major impacts excavate rocks from substantial depths, and what we've seen -- either from orbit or close up -- is almost entirely just the surface layer.

The oxygen-isotope ratios, which are fairly distinctive, should be shared by pretty much any rock from Mars.

Grossly implausible, given that the gas trapped in bubbles in a couple of them is unmistakably Martian air.

As George points out below, we have a lot of orbital photography of most of the Martian surface, and MGS has taken a large number of measurements with its Thermal Emissions Spectrometer (TES), which gives a lot of clues to the minerology of the surface. The fact is that the orbital instruments have found relatively little of the surfacial layer matches the minerology (i.e., high-pyroxene basaltic) of the Shergottite meteorites. If they're abundant anywhere on Mars, they're sure not abundant on the surface.

Again as George points out, there likely aren't all that many pieces of Mars that have found their way to Earth -- especially that are recoverable and identifiable as meteorites, much less of Martian provenance. And while some of the meteorites that are thought to be from Mars are categorized as such by trapped gasses (gasses that have remained in them after spending millions of years in space and hundredds of thousands of years on Earth), most are categorized, as well, by the isotopes of various elements present in the rock. For example, most rocks contain some amount of oxygen, incorporated into the minerals as oxides of one form or another, and you can determine where in the original solar nebula a body formed by the relative abundances of different oxygen isotopes. Many of the meteorites that are categorized as Martian are thought to be so based on oxygen isotope ratios. So thde trapped gasses aren't completely necessary to identify pieces of Mars.

That's almost definitely not true, based on the points I made above. The Mars rocks on Earth are, with very little doubt, pieces of Mars.

Yep -- especially when you consider that we have a pretty good TES coverage of the surface and know more than just what the surface looks like.

When you consider that the Mars rocks on Earth had to have been ejected by a pretty forceful impact (or number of impacts), you have to figure that, just maybe, the Mars rocks that have fallen onto Earth might have come from fairly deep in the Martian crust. So it's maybe not all that surprising that we haven't seen all that much of this material right on top of the Martian surface.

Very much so. The fact that we've been able to identify ANY Mars rocks here on Earth is pretty amazing, in fact.

Doug snipped-for-privacy@NOSPAM.mn.rr.com

True, Beagle 2 blew chunks, but you have a great orbiter. It blows something much nicer. Like, I donno, I suppose maybe Brit hottie Keira Knightly

So add the two together and things pretty much cancel out to neutral or positive.

Beagle == Lawn Dart

OK, that reinforces my question: if these types of rocks are so rare at the surface on Mars, how come they're the _only_ Martian meteorites we find on Earth? (I didn't realize you should be able to recognize these rocks from orbit; I was assuming you had to be on the ground.)

But an impact that launches deep rocks will also launch surface rocks, right? Some of these might melt and therefore become >> Finally, number of meteorites that have been found that didn't

I understand that--what I don't understand is why the only Martian meteorites we've found on Earth turn out to be rare rocks on Mars (unless, as you say, they're from deep in Mars).

Mike Maxwell

Easy answer is that they are not the only Martian meteorites found on earth. There are at least three different types known.

meteorites include three rare groups of achondritic (stony) meteorites (16 objects total) with isotope ratios that are said to be consistent with each other and inconsistent with the earth. It should be pointed out, however, that the isotope ratios do not actually match Mars ratios especially well, to the extent that Mars ratios are known, although they do differ substantially from Earth isotope ratios and from what is known of Lunar ratios.

All the meteorites are igneous rocks. Lherzolitic shergottites (one from Antarctica, two from California) are identified by their Deuterium/Hydrogen ratios. The crystals appear to be 154-187 million years old and they appear, from cosmic ray analysis, to have spent 2.5 to 3.6 million years in space. There are also basaltic shergottites, some of which appear (from the presence of hydrated carbonates and sulfates) to have been exposed to liquid water prior to injection into space. One of the shergottites, known as ALH84001, is much older than the others - about 4.5 billion years. In this respect, it resembles a typical meteorite rather than the other shergottites. The other two types of Martian meteorites are Chassignites and Nakhlites. All appear to have been on earth no more than 35,000 years. Together, these objects are called SNC meteorites.

I won't pretend to have all the answers, when it comes to meteorites, since they are not my specialty. Having said that, here is a list of the known Mars meteorites, an information about them:

Considering that we've only scratched the surface, literally, of Mars, I don't hink any scientist would make the claim that they are rare on the surface simply because we don't know anything about their abundance there.

They're *not* the only Martian rocks we find on Earth. There are three general classifications of Martian meteorites that have been found here, and Bounce Rock falls into one of them. The other two are closer to what's been seen from orbit and on the surface -- though one of the classifications has more carbonates than what we've been seeing on Mars.

And of course you can recognize some elements of minerology from orbit

-- how else do you think the MER planners figured out that there was hematite at the Meridiani Planum site? In fact, that site was called the Hematite Site during the landing site selection process.

A rock melt doesn't necessarily lose its gasses -- it incorporates the gasses in the environment in which the melt occurred.

Now, most of the Martian meteorites do not *seem* to be impact melts -- they mostly look like highly shocked varieties of volcanic rocks. But as anyone who has studied the examination of the lunar samples knows, it can be very difficult to tell between impact melts and volcanic rocks. Much of the impact melt sampled at Fra Mauro on the Moon, for example, is basaltic in nature -- but still seems to be impact melt.

Of course, very energetic impacts *do* toss around both surface rocks and deep crustal materials. I'm tempted to think that the Martian meteorites we've seen were ejected in basin-forming impacts, since those generate the most energy. But the exact dynamics of how such meteorites are ejected entirely from Mars' gravity well are poorly understood -- perhaps those dynamics select either surface rocks or deeper crustal rocks for ejection out of Mars' grasp. I don't think anyone has a model that can predict that with very much accuracy.

Again -- there are more than one type of Martian meteorites. Granted, none of them seem *extremely* abundant on the Martian surface, but then again, we don't know exactly when they were ejected from Mars. There are guesses, but they're not pinned down all that well.

Doug snipped-for-privacy@NOSPAM.mn.rr.com