So even though the two diamond fields are now thousands of miles apart, they're remnants of a single, original deposit.
Haggerty estimated that the asteroid must have been about half a mile (one kilometer) in diameter.
Fizzing Froth
The unusual bubbles in the diamonds probably came from fizzing gases when the diamonds were forming, Haggerty added.
This adds further credence to the extraterrestrial origin theory, since conventional diamonds form under immense pressure deep beneath the Earth's crust, where gas bubbles simply couldn't form.
But diamonds can be formed in the laboratory without intense pressure via a process called carbon vapor deposition.
"That [process] can certainly happen in interstellar space," Haggerty said. "There should be a lot of diamond out there."
Controversial Finding
But not everyone believes that Haggerty's team has made its case.
"The comparison with nanodiamonds in meteorites is misleading," said Scott Messenger an astrophysicist at NASA's Johnson Space Center in Houston, Texas, who studies ancient stardust embedded in meteorites and cometary dust.
Nanodiamonds "are vanishingly small—only a few thousand atoms in each," he continued by email. "These diamonds are enormous."
In addition, diamond grains from interstellar dust contain "extremely exotic" isotope compositions, he said, whereas carbonado diamonds do not.
Frank Stadermann of Washington University in St. Louis agrees.
"The fact that we have never seen anything similar in extraterrestrial samples does not represent an actual proof that this is not extraterrestrial," he said by email.
"But this argument works the other way, too. The fact that we have never seen anything like this in previously studied terrestrial samples does not represent an actual proof that it is not terrestrial in origin."
Haggerty countered that carbonado diamonds contain a mineral called osborneite, which has been found only in meteorites and comet dust recovered by the recent Stardust mission. (Related: "Stardust's Comet Clues Reveal Early Solar System" [December 15, 2006].)
He also pointed out that carbonado diamonds have never been reported among any of the other 600 tons of "conventional" diamonds mined, sorted, graded, traded, cut, and polished in the last century.
"Surely, just one would be expected if [they are] terrestrial in origin," he said.
On a ten-point scale, Haggerty said, he's reached "about a nine" in terms of demonstrating that the diamonds don't come from Earth.
But he's ready to seek further proof.
"The acid test," he said, "would be to identify a carbonado body in the Asteroid Belt."
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