Comet Dust is Very Similar to Asteroids

by Fraser Cain on January 25, 2008

Stardust image of Wild 2. Image credit: NASA/JPL
Just so it’s clear in your mind: comets are dirty snowballs, asteroids are rocks. Got the difference? Wait… not so fast. Scientists studying the cometary dust picked up by NASA’s Stardust spacecraft, and they’re finding it’s surprisingly asteroid like.

When Stardust flew past comet Wild 2 in 2006, scientists knew they would be scooping up materials created with the very formation of the solar system. But they didn’t think the dust from Wild 2 would resemble meteorites more than ancient, unaltered comet.

Comets are thought to contain large amounts of primitive material in the Solar System. Both the ancient ices that formed out of the stellar disk, but also the rain of interstellar material falling into the Solar System.

According to researchers at Lawrence Livermore National Laboratory, the particles that fell off Wild 2 formed very close to the Sun when it was young. They had been baked and blasted by the intense ultraviolet radiation of a newly forming star. Furthermore, they didn’t find the kind of primordial materials and ices that should have been present on an ancient comet like Wild 2.
Tracks of material captured by Stardust. Image credit: LLNL

“The material is a lot less primitive and more altered than materials we have gathered through high altitude capture in our own stratosphere from a variety of comets,” said LLNL’s Hope Ishii, lead author of the research that appears in the Jan. 25 edition of the journal, Science. “As a whole, the samples look more asteroidal than cometary.”

But Wild 2 is clearly a comet and not an asteroid. It’s got a tail; what could be more cometlike? It’s a reminder that there isn’t a clearly defined line between the two objects – there’s a continuum between them.

The researchers were expecting to see very specific minerals in the Stardust samples that should be coming from comets: glass with embedded metal and sulfides, and sliver-like whiskers of the crystallin silicate enstatite. They found only a single sample of enstatite in their samples and it was oriented the wrong way.

There were similar minerals found, but the researchers realized that they were being created when particles from the comet slammed into the Stardust collector. They were able to recreate this process in the lab.

For future studies, the researchers are hoping to get their hands on larger-grained materials, called micro-rocks. These would suffer less alteration from the impact with the Stardust collectors.

Original Source: LLNL News Release

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Fraser Cain is the publisher of Universe Today. He's also the co-host of Astronomy Cast with Dr. Pamela Gay.

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