Dust from the stars

By Phil Plait | April 4, 2006 5:07 pm

‘I attended a talk yesterday by Don Brownlee, who is the head guy on the Stardust mission (which brought back samples from a comet: see here, and here and here). Stardust returned comet particles to Earth several months ago, and scientists all over the planet have been eagerly looking at them, investigating their chemical and atomic structure. They’re looking to see what kind of environment the particles formed in (and therefore where the comet formed), where they’ve spent their time, maybe even if they came from our solar system or an entirely different one.

I was sitting off to one side, so the perspective on this image is a little odd. What Dr. Brownlee is showing there are three images of a particle from the comet. The big image is a microphotograph of a piece of LICE forsterite. I don’t know what LICE stands for, and a google search didn’t turn anything up (though I have to admit it’s weird that some web pages out there have discussions of both forsterite and head lice on them). Forsterite is a mineral that you wouldn’t think twice about finding on Earth, but finding it on a comet is very, very odd: it’s made in hot environments, like 2000 Celsius hot.

That’s really weird because comets are cold. They have lots of ice in them, and spend most of their time in deep space. If you put comets someplace hot, they evaporate pretty quickly (which is why they form tails when they get near the Sun). So how could they have minerals in them that formed at high temperatures? Is James McCanney right?

Actually, one possible solution isn’t hard to imagine. When the solar system was young, and planets and comets still forming from a disk of gas and dust, the Sun was fairly active. We see young stars shooting long jets of matter out from their poles due to magnetic forces. This transports material formed near the surface of the Sun to the outer solar system, where comets form. So in fact you might expect to see some high-temperature minerals in comets… if you had thought of it first. I have not heard of anyone predicting that, which is too bad. They’d be pretty hot stuff right now if they had!

Hot stuff. Oh man, I crack myself up.

Anyway, Dr. Brownlee pointed out another neat thing. The image on the upper right in the picture above is an extremely high-magnification zoom of the particle. That grid-like structure you see is not some photographic effect: it’s the actual crystal structure of the particle itself. You’re seeing rows of atoms lined up like soldiers on parade in the crystal.

Think on that for a moment: before the telescope (and really, even after it for some time), we had to observe comets with our eyes, and the smallest feature we could hope to see on a comet was the size of the Earth. Since the actual physical object forming the comet is at most a few kilometers across, this was hopelessly coarse resolution.

But now we have samples of comets, and can examine them in our labs. We can see individual atoms in the comet! According to Dr. Brownlee, this represents, roughly, an increase of 17 orders of magnitude in our resolving power: 100,000,000,000,000,000 times, 100 quadrillion times!

That’s not too bad. I’d love to see a day when that sort of power is brought to bear on the other objects in our solar system. There’s still so much to learn!’

CATEGORIZED UNDER: Astronomy, Cool stuff, NASA, Science

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