A rare meteorite that may have been born in Earth's neighbourhood has been found using a new 'fireball' observatory in Australia.
Scientists can learn how the solar system formed by studying meteorites that originated in different places within it. The trouble is, they don't know where the vast majority of meteorites actually came from.
"Trying to interpret what happened in the early solar system without knowing where meteorites are from is like trying to interpret the geology of Britain from random rocks dumped in your back yard," says Phil Bland at Imperial College London.
To remedy that, Bland's team set up the Desert Fireball Network in Western Australia's Nullarbor Desert in 2006. This trial network, currently with four robotic cameras spread over roughly 250,000 square kilometres, exposes photographic film to clear skies throughout the night.
If the cameras record a bright meteor, or fireball, as a rock falls through Earth's atmosphere, scientists can calculate its trajectory by triangulation, estimate the rock's likely landing site, then look for it.
Small parent
Following the network's first observation of a fireball on 20 July 2007, search parties found three fragments of the resulting meteorite, named Bunburra Rockhole, in 2008 and 2009.
The meteorite is made of basalt, the most common type of solidified lava on Earth. Scientists typically assume that basaltic meteorites are chips off the giant asteroid Vesta
.
But Vesta is so large – roughly 530 kilometres across – that gravity caused its component materials to settle into different smooth layers soon after its formation. The compounds in this meteorite, by contrast, are more uneven, suggesting it came from a smaller asteroid a few tens of kilometres wide.
Molten rock
Orbital calculations suggest this parent asteroid orbited in the innermost side of the asteroid belt between Mars and Jupiter until a collision chipped Bunburra Rockhole off the asteroid around 10 or 20 million years ago.
But though its parent body once orbited inside the asteroid belt, it may have been born closer to the sun. A theory proposed in 2006 argues that molten rock swirled around the young sun only in the current region of Venus, Earth and Mars, with many molten blobs subsequently flung out to the innermost asteroid belt.
In that case, Bunburra Rockhole could represent the type of material that clumped together to build Earth. "Our big question is – what were the building blocks for the terrestrial planets?" says Bland. "This rock gets us a little bit closer to that."
Journal reference: Science (DOI: 10.1126/science.1174787)
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Have your say
I'd appreciate it if someone could explain how you can determine that a meteorite came from the inner side if the asteroid belt. I mean all they have is a blurry picture taken over a full night's exposure. Since you don't even know what time of the night the meteor came in, you don't even know where in the solar system it was coming from, and even if you did, how do you know it came from the inner side of the asteroid belt instead of the outer side, or from the kuniper belt?
For that matter, how do you know the composition of Vesta? I don't think we have sent any probes there yet. It sounds to me like there is a theory that gravity should cause the heavier materials to settle down, but no proof. Vesta might have formed very slowly when it wasn't molten, or might have been fragmented by a large collision and then reformed.
When I read articles like this I'm reminded of a cartoon of an archeologist who has 2 bricks in his hand and sees an entire city in his mind. It seems like there are a lot of untested theories being accepted as fact.
I really would appreciate it if someone could explain why people seem to be so confident about things like the source of the meteor or the composition of Vesta.
Nebulous questions are hard to answer concisely, but I'll try.
As a minor or major planet forms in a well understood way. This is because physics doesn't change no matter where you are. The laws that governed the formation of Earth are also what affects the formation of an asteroid, albeit on a different scale. As a body cools, it either has enough mass (and heat) to differentiate (separate into different layers) or in a smaller object, it will 'flash cool' into an object with a homogeneous composition. In the solar system, we've observed directly or with our probes a wide range of objects that have differentiated completely, incompletely or not at all, so this math is pretty solid, to forgive the pun. There's no untested theories here. We know this fallen rock must be from a small object because it leans towards the latter end of the scale.
While there are similarities among all rocky bodies, since they all formed from the same disc material and planetismals, every object has a detectably unique chemical signature to it. This chemical signature of soils and rocks can be detected directly, through samples, or indirectly, through spectral analysis of light the object reflects, or even through radio analysis. Through our robotic emissaries, for example, and through our telescopes, we've known for a long time the unique chemical signatures that a Martian rock would possess, and we've been able to compare these to discoveries here and find meteorites that are clearly Martian. This also does not rely on much 'theory'. There is real data. Even before a rover set tread on Mars, we would know well what minerals to look for, and what ratio of isotopes to expect from a Martian rock.
As for how they worked out where it came from, orbital mechanics are a bit beyond my particular expertise, but I imagine it was a combination of factors, including its unique chemical signature, as well as its trajectory and velocity when it entered the atmosphere (which can, in fact, be worked out from the 'blurry' photograph, despite its appearance). From there it's just a matter of extrapolating what the orbital parameters were before the bug hit the windshield, and comparing it and its composition with known families of asteroids. Am I close, smarter people?
Thanks for the answer. I have to say that I still don't quite buy it. I saw a program on the planetary systems of other stars. Before we were able to actually see any such planets, we assumed that other star systems would look like ours, with planets in nearly circular obits, and with small planets close to the star and larger ones further out. Once our telescopes were able to actually observe other star systems we found that most planets do not orbit in nearly circular orbits, and most of the large planets that we see are very close to their stars. In other words, we extrapolated on what we saw close at home and assumed that it applied everywhere, when actually our own solar system is quite unusual.
I have to wonder what Vesta is really going to look like when we get there.
How Do You Know That?
Fri Sep 18 05:16:53 BST 2009 by Kevin
http://kepler.nasa.gov/
The reason we had only found large planets close to their star's so far is because the techniques and resolution of the available instruments only could detect large planets in close orbits.
With the launch of the Kepler mission with the capability to detect Earth sized planets in larger orbits, there should be considerably more Earth like planets found shortly.
http://kepler.nasa.gov/
"I have to wonder what Vesta is really going to look like when we get there." - sickpuppy
You are in luck, the Dawn probe is scheduled to arrive at Vesta in just under 2 years. I can't wait to see what it really looks like.
As for other planetary systems, I'd be very surprised if ours turns out to be unusual (aside from the presence of advanced multicellular life, which is probably very rare). As others have said, there's has been a very strong sampling bias - the technology we've been using can only spot the bizarre ones and it can barely spot those! We will know more soon.
"In other words, we extrapolated on what we saw close at home and assumed that it applied everywhere, when actually our own solar system is quite unusual." --sickpuppy
We can be absolutely certain that a solar system like ours can form. Until very recently, we would have been unable to detect any others that matched ours.
The fact that we have found only relatively few solar systems with current methods suggests that they (with "hot jupiters") are actually quite rare, leaving the possibility that those more like ours are more common. Or they are more rare. We just can't know either way at this point.
How Do You Know That?
Fri Sep 18 06:44:23 BST 2009 by D Dilworth
http://Cosmologyscience.com
While I don't completely buy this explanation yet either, this answer is stellar. It is a first class comment, directly on topic, that teaches fundamental knowledge without a trace of arrogance. Three cheers. John Fleming has set a standard we should all try to emulate. Thank you John.
I'd like to say "Hear Hear" to D Dilworth's comment about John Fleming's explanations. What a welcome suprise to find a sensible thread, for a change. Thanks
Hear, hear ! :)
Wikipedia: http://en.wikipedia.org/wiki/4_Vesta
How Do You Know That?
Fri Sep 18 00:58:35 BST 2009 by Tim
http://www.androgen.net.au
Yeah exactly ... they know about Vesta because they looked it up on Wikipedia. How else would a scientist learn anything?
Also, note that the image comes from a network of (four) cameras and so the direction and velocity of the track can be determined by comparing the data from these.
And, to comment on your archeologist analogy, I am quite sure that an archeologist who has seen hundreds of sites and thousands of bricks can tell a lot from a couple of bricks and the local topography. For example, mud bricks made in small quantities for a small settlement will be noticeablt different from those mass produced for a large city...
Sometimes what seem like untested theories or assumptions to an outsider are based on many years of evidence gathering and analysis.
Where is this Vesta? Could it impact Earth?
Something 530 kilometers across would totally destroy life on Earth. The dinosaur-destroying meteorite was only 6 km across.
Don't worry, Vesta's not about to hit anyone around here, its one of the "minor planets" as they were call before the name was changed to asteroids, it lives between Mars and Jupiter.
So ! Your Better Off Finding A Ufo!!
Sun Sep 20 22:41:06 BST 2009 by mary a smit
http://google
Hazel Miur , hi from the north sort !? bc canada if any usa dare to note ~ aft' years of sort of netting , info via , there seems to be a blockage to real info aswell a Blockage to Knowledge to the sheep= public. the cheap intenet via apple and billy gates. call me via the phone as i see that huh? sensitive or privacy is oh really not an issue via THE INTERNET. YOU'LL find me if so important seems like all the physics is so ... messed up. or some or group! just doesn't believe in the ... wow democracy?
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