Invaders from Vesta!

By Phil Plait | September 18, 2011 10:58 am

I did two related things yesterday: I wrote about the asteroid Vesta, and I went to the Denver Gem and Mineral show.

How are those tied together? Glad you asked.

In the last paragraph of the Vesta post, I said we have samples of Vesta that fell as meteorites. As it happens, they had a sample of one of those rocks at the show! Here it is:

Other such meteorites have been found on Earth as well, and are generally referred to as HEDs, short for Howardite/Eucrite/Diogenite — the three main types of these rocks.

So how do we know these meteorites were once part of Vesta? A couple of ways, actually, but they rely on spectroscopy. That’s the process of taking the light from an object and breaking it up into individual wavelengths (using a prism or a finely etched grating, for example), essentially creating a rainbow with as many as hundreds of thousands of colors. The spectrum of an object can be affected by its composition, how fast it’s spinning, whether it’s moving toward us or away from us, and much more. Reading its spectrum is like reading its DNA.

In the 1970s, studies of HED meteorites (PDF) indicated their spectra were much like the spectra of Vesta, showing their compositions were very similar. Now, asteroids are pretty diverse, so finding similarities between an asteroid and a meteorite is a pretty good piece of evidence that the latter came from the former. As it happens, though, there are other asteroids with similar spectra to Vesta, and they are in similar orbits as well. This is what you’d expect if, say, Vesta got hit by some large object, dislodging big chunks which then orbited the Sun on their own. This is seen commonly in the asteroid belt, and groups like this are called asteroid families.

Some of the asteroids in the Vesta family are not apparently similar to each other, though. Spectra show that some are chemically similar to rocks that formed in something like a planetary crust, while others look more like rocks from a planetary mantle. HEDs show the same property, in fact. So how can that be?

The answer is that Vesta apparently was once hot enough to have had heavier minerals sink to its core and lighter ones float to the top. That’s called differentiation, and it’s happened on Earth as well. That’s why we have an iron core and a rocky crust.

So when Vesta formed, it got hot enough that metals sank to its core and rocky minerals floated up to its mantle and crust. Over millions of years it got impacted by other asteroids, getting huge pieces knocked loose — in fact, as I pointed out in yesterday’s post, the south pole impact on Vesta was a real whopper, and could easily have created all the Vesta-like asteroids known. Remember, Vesta is the second largest asteroid (or maybe third, depending on the uncertain size of the asteroid Pallas), so it has material to spare.

As these asteroids spread out, some stayed in similar Vesta-like orbits. Others got blown out farther, and had their orbits affected by Jupiter’s gravity. Some of those had their orbits altered enough by the mighty planet that their paths take them near the Earth. Over time they too suffered impacts, creating smaller objects that then have orbits that cause them to hit the Earth. We find those as HED meteorites. Perhaps some came directly from Vesta, and others from Vesta’s violently-birthed daughter asteroids, but in the end we think they can trace their lineage back to Vesta.

So there you go. It’s a bit of a twisted tale, but it all hangs together, as scientific stories must. We don’t know all the details, of course — there could be other asteroids similar to Vesta that produce some of these meteorites, for example — but that’s why we explore. We sent the Dawn spacecraft to Vesta specifically to help answer questions like that, to make a mineralogical map of the asteroid to find out exactly what it is and how it’s put together.

And in the meantime, we have actual samples of asteroids simply sitting on the Earth’s surface, waiting to get picked up and examined. Normally, planetary scientists have to wait years or decades for probes like Dawn to reach their targets, but sometimes nature is kind, and brings those targets — or at least small pieces of them — right here to us.


Related posts:

Vesta’s odd bottom
Vesta’s double whammy
Follouwp thoughts on the meteorite fossil claim
Yankee scientists were right about rocks form the sky

CATEGORIZED UNDER: Astronomy, Cool stuff, Science
MORE ABOUT: Dawn, HED, meteorites, spectra, Vetsa

Comments (30)

Links to this Post

  1. The Meteorites That Fell To Earth | wpgrabber | September 21, 2011
  1. Honestly it doesn’t seem real conclusive to me. I’m not a fan of saying that we “know” something that we really don’t. The evidence is pretty good but seems pretty far from being a slam dunk. Doesn’t really matter though. Having stuff from off-planet is always cool. I’d just be happier if the plaque said something a little less absolute.

  2. Kathy King

    Fascinating! This will make a great reading assignment for my students!

  3. Infinite123Lifer

    I think the absoluteness would rely solely on the accuracy of several spectroscopy’s.
    Of course…absolute…is a pretty BIG word.

  4. Nebogipfel

    As Montgomery Scott once said “Aye, and if my grandmother had wheels, she’d be a wagon!” :)

  5. Chief

    I don’t suppose that once the orbit is lower the probe can look for a matching hole that this rock came from….

  6. QuietDesperation

    (Zooms in on sample)

    Oh, please… someone went outside, got a chunk of pavement from a pothole, and put it in a case.

    Monomict breccia my shiny metal a-[link terminated]

  7. Pete Jackson

    Latest pictures of Vesta from the Planetary Society Blog remind me of a giant walnut! I don’t want to be around when this nut cracks open!

  8. Jess Tauber

    Mining engineering question here: if Vesta has a metallic core, how much metal are we talking about in toto, and, if one wanted to get at it, are the overlying layers of material now solid and stable enough, in the weak gravity, that dug shafts wouldn’t collapse under their own weight?

  9. AnthonyK

    I’m sure this has been answered many times before on BA, but what is the truth about the idea that, in ancient Egypt, iron was the most precious of all metals; that it was used in the funery implements for extracting vital organs from the soon-to-be-mummified bodies of Pharoahs and potentates; and that all of it came from meteorites?

  10. Pete Jackson

    @9Anthony: I doubt that iron was ever especially precious since it rusts, unlike gold. Iron of meteoric origin has a high proportion of nickel, which is not present in terrestrial iron ores. So if the ancient Egyptian iron has significant amounts of nickel, then it was probably of meteoric origin.

  11. So Phil, did you buy it? Or score another meteorite to add to your collection?
    My Campo del Cielo was a hit at Dragon*Con. Holding a piece of star stuff in your hand and feeling its considerable heft really drives home the point that Death really does come From The Skies!

  12. QuietDesperation

    Holding a piece of star stuff in your hand

    Well, according to Sagan we are all star stuff, so you hold star stuff in your hand when you hold yourself.

    Yeah, that sounded a lot better when it was still in my head.

    And that one, too.

    I’ll stop now.

  13. Considerable heft… Heh. Heh. ;^)
    But seriously folks, Carl was right, we ARE all star stuff. My meteorite is just a recent arrival.

  14. Joseph G

    @#8 Jess Tauber: In a sense, the material’s stability probably doesn’t really matter all that much. Vesta’s surface gravity is about .02 Gs (and it only drops as you dig deeper), so lining your tunnels with sturdy cardboard would probably do the trick :-P

    Actually, I’m no engineer, but I’m thinking if you brought some water and quicklime with you, you could probably use the material you excavate to mix up some shotcrete type stuff and coat the walls with it as you go.

    @12 QuietDesperation: Cool! I’m holding some nice hot star stuff in my hand right now. Anyone want to taste it?

    Er… To clarify, I believe hot chocolate is made of star stuff too, right?

  15. @1. CafeenMan Says:
    “Honestly it doesn’t seem real conclusive to me. I’m not a fan of saying that we “know” something that we really don’t. The evidence is pretty good but seems pretty far from being a slam dunk.”
    The chain of logic is fairly long and moderately tenuous, but there are several other items of data that are well established on different grounds that indicate that meteorites can be traced back to particular sources.
    Firstly, in the late 1960s and early 1970s, humans travelled to the Moon, and brought back lumps of rock. These have been analysed in detail and one of the peculiar side discoveries was that some subtle aspects of lunar rock chemistry (IIRC, oxygen isotope ratios in particular for oxygen in non-volatile silicate and oxide minerals) were also seen in relatively uncommon types of meteorites). This bulk-mineralogy data provides evidence that meteorites can be transported fomr the Moon to the Earth.
    At around the same time, automated laboratories which had been landed on the surface of Mars (the Viking missions) returned readings of the chemistry of the atmosphere of Mars. And when some members of peculiar families of meteorites had comparable measurements made on them, they also had the same composition of gas trapped inside the meteorite. Since we knew the gas compensation they’d been contaminated with (Earth’s atmosphere composition), and the gas composition that came out of the meteorites, the composition of the gas trapped in the rock from the shock of launch can be calculated. And that composition matches the measured composition of Mars’ atmosphere.
    If you accept those pieces of evidence, then tracing a family of meteorites back to Vesta becomes much less of a step.

    @8. Jess Tauber Says:
    “Mining engineering question here: if Vesta has a metallic core, how much metal are we talking about in toto, and, if one wanted to get at it, are the overlying layers of material now solid and stable enough, in the weak gravity, that dug shafts wouldn’t collapse under their own weight?”
    529 km mean diameter, but a minimum of 458km diameter. Assuming the metallic core is more or less proportional to the Earth’s core, it’ll be around 1/4 of the asteroid’s diameter, say an optimistic 132km (around 8.4×10^15 tons, unless I’ve slipped a digit). But your minimum tunnel length will be around 326km.
    You’d be much quicker looking for a smaller asteroid which has had most of it’s “mantle” (literally) of silicates stripped off in a previous collision.
    The composition of the mantle rocks appears relatively low strength. Look at the preserved rock waves from the large Vesta-mashing impact it has had. Tunnelling that is not going to be fun, low-gravity or not.

  16. Joseph G

    Phil mentioned that there’s a good deal of diversity in the composition of asteroids – I’m wondering why that is. Didn’t everything in the solar system form from a collapsing molecular cloud? Somehow I’d think that all those gas and dust particles would be pretty well randomized by the time they started sticking together? No?

  17. Gary Ansorge

    8. Jess Tauber

    One of the principle constraints to deep mines is the increase in temp associated with going deep.

    From Wikipedia:
    “Geothermal gradient is the rate of increasing temperature with respect to increasing depth in the Earth’s interior. Away from tectonic plate boundaries, it is 25–30°C per km of depth in most of the world.”

    On Vesta, however, the temp increase would likely be trivial, so deep mines are quite usable.

    The worlds deepest mine is, from Wikepedia:
    “The TauTona Mine or Western Deep No.3 Shaft, is a gold mine in South Africa. At some 3.9 kilometers (2.4 miles) deep it is currently home to the world’s deepest”

    If Vestas gravity is taken as .02 G, and we divide that into our greatest mine depth, we get a Vesta mine of about 190 km deep however, since one of our constraints here on earth is the temp increase and Vesta is probably quite cold internally, I expect we could drill a mine all the way thru Vesta,,,or, to put it another way, we could make tunnels several hundred meters tall/wide throughout the asteroid and pack a half trillion people and all their “stuff” in it.

    THAT would be a really BIG space colony.

    Gary 7

  18. Brian Berry

    Minor nitpicking, but Berthoud is in Larimer county, not Weld.

  19. icemith

    @ 15. Aidan Karley,
    “…Assuming the metallic core is more or less proportional to the Earth’s core, it’ll be around 1/4 of the asteroid’s diameter, say an optimistic 132km (around 8.4×10^15 tons, unless I’ve slipped a digit). But your minimum tunnel length will be around 326km.”

    Given that the “132km” diameter of the core is in the ballpark, I cannot understand how the resulting figure of 326km for the shaft is obtained. (Unless you are planning an oblique tunnel, which may have considerable advantages.).

    No, I think diameter and radius were confused in the calculations. 500 odd km, less the diameter of the supposed core of 132km, yields less than 400km, which is the total of the rest of Vesta’s diameter, which means that it has to be halved to get the remaining radius, ie, through the crustal portion of the asteroid. And one only needs to dig down approx. 200km, even less, 110km, if one sites the mine at the South Pole where the flat bottom has been already removed, unless it suffered from massive compaction in the “Big Bump”.

    (Unless one decides to have a sloping tunnel as mentioned earlier!).

    Given also that the mass of the mined metal ore would be minimal in the circumstances, and being capable of being moved relatively easily, I suggest a method of “blowing” the ore up the shaft, would be economical. One would have to produce some gas (hydrogen?), to be the vehicle of transport.

    Hey, even a through shaft from one side to the other of the Asteroid, being tangential with respect to the “surface” of the iron core, may be the way to go. I’ll leave it to the mining engineers to work out the details. If the tunnel was absolutely straight, one could see right through the asteroid!

    Ivan.

  20. Gary Ansorge

    19. icemith Says:

    “I suggest a method of “blowing” the ore up the shaft”

    A mag lev train would do just as well and would obviate the loss of said gas. We really don’t want to lose any volatiles in space,,,they may be hard to come by.

    In such a large asteroid, it would also be relatively easy to build a mag lev train around the wall of a large cavern(say, several kms). Run the train at 100 km/hr and you have about a one G environment. Great place to hang out in ones off hours,,,

    Gary 7

  21. Artor

    How about a linear accelerator run through the middle, aligned with a drop zone crater on Luna? Then the ore from the core could be delivered homeward express- style?

  22. Ian

    “Well, according to Sagan we are all star stuff, so you hold star stuff in your hand when you hold yourself.”

    Yo dawg…

  23. Jess Tauber

    Re 21: Heck you could convert the asteroid into a low rent Death Star wannabe mass driver, and shoot masses in opposite directions (maybe rocky waste away from the target) to prevent net movement of the parent body. That way the Earth will know who the real Boss is (call it the Springsteen Cannon if you must…).

  24. icemith

    @ 20. Gary Ansorge …

    Yeah Gary, I did momentarily consider a type of linear accelerator/mag lev device, but wondered if the Solar Power Station on the surface would be feasible. Doubt whether Nuclear Power would make it now, or in the not so near future, given recent problems and vulnerabilities.

    @ 21. Artor …

    Shooting a stream of ore through Space towards the Great Industrial Precinct on the moon would be cool – until some Astronomers complain about obscured vision of some deep space observation!

    Or the “No-go” restrictions anywhere near the stream of ore, as any disturbance in gravity would end up spraying it all over the moon’s surface. I guess one could employ focusing coils, a la old CRT technology as used in oscilloscopes and TVs, anchoring these in fixed orbits relative to the Moon at the lagrangian points.

    (Oh boy, I also looked up “geodesic” trying to find out the “geo-xxx” word relating to that problem, and the maths on the second page in Wiki. was horrific! I think I hurt my brain. I’m going back to bed.)

    Ivan.

  25. Jess Tauber

    One can multiply the power for the surface solar power station by putting a gigantic annular parabolic mirror on the far side of Vesta, focusing back to it, using graphene as the mirror substrate, so the total mass is low, and the entire thing can be folded up into a conveniently small volume. What surface area would do, folks, for the whole shebang? That’s all machinery, life support, energy for mining, for acceleration/deceleration of vehicles, including from/to offworld, etc.

  26. Tom

    Actually there is little need to drill a tunnel through Vesta; there are many small, nickel-iron asteroids, both in Earth-approaching and Earth-crossing orbits as well as in the main belt. MIT did a study of asteroid mining years ago, they wanted to return refined metal to Earth’s surface by molding the metal into re-entry bodies, similar to satellite return capsules.

    There were some more interesting studies by Brian T. O’Leary and K. Eric Drexler. Brian wanted to return an entire small asteroid to Earth orbit, with a mass-driver reaction engine using asteroid material as reaction mass. Eric Drexler wanted to use light-sails to return packages of asteroid regolith to Earth orbit for processing.

  27. Michael Berry

    This article is interesting, but I love the comments here. I clearly have nothing to contribute except to say that this discussion is fascinating! Thanks for making my boring shift at work entertaining, everyone.

    (And now…please continue!)

  28. Joseph G

    @26 Tom: For mining, perhaps, but in terms of habitation…
    One of the major problems with space habitats is the lack of an atmosphere (and magnetic field, unless you’re in low Earth orbit) to shield the station from cosmic rays and solar radiation. Drilling through a large asteroid gives you the raw materials and protection from radiation you can get from a planet, without the pesky gravity well. You can build a rotating habitat inside the asteroid to provide ‘gravity’, and you’re golden. Some asteroids also have a lot more volatiles then the moon, and more per square mile even then Mars. Ceres is thought to have more water under its crust then the combine freshwater reserves of Earth. And the moon is fairly metal-poor, at least on the surface, as far as we can tell.

    Between the low gravity environment, the availability of certain key materials, and the low delta-V required to get home, a very good case could be argued that large asteroids would be the easiest targets for colonization, before even the moon.

    @Gary Ansorge: I love the “train habitat” idea. The great thing about it is that you can simply add more “cars” as you need to, as opposed to a “wheel” type free-floating station, where you’d need to balance the thing fairly carefully once you spun it up, so it wouldn’t wobble.
    Also, unlike the idea of a station with a despun “zero G” module (for docking, etc), you wouldn’t have to deal with the issue of an enormous, motorized, air-tight rotating joint. You can just have “spurs” off the main track that let you bring modules in or out of the “train” (and even store them). Regular old airlocks would be all you’d need.

  29. Fred Olsen

    The berthoud display was mine. I do hope you enjoyed it. I am fully aware that the Vesta connection is conjecture. But Dawn is on the job! Also, while the town of Berthoud is mostly in Larimer County, the Berthoud eucrite meteorite landed 3 miles east of the town in Weld County. The only county in America to have two “Vestian” meteorites land within it’s boundries.

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