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Pieces of a comet March 16, 2006

Posted by dr. gonzo in Space.
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Comet Wild 2 from Stardust (courtesy JPL)The NASA Stardust news conference the other day was a pretty interesting watch, if you know anything about comets.

The Stardust mission to collect comet samples and return them to Earth seems to have been a grand success for NASA. Perhaps the most surprising find in the analysis of the comet particles thus far was the discovery of minerals which form in only very high temperatures.

Why is this so surprising?

Comets are the so-called “dirty snowballs” of the solar system. They exist in a realm of the solar system near Pluto, where cold temperatures (extremely cold temperatures which hover just above absolute zero in places) dominate and occassinally pass close to the Sun in their orbits. Thus, scientists were surprised to find such high temperature minerals in such a cold region of our solar system.

Donald Brownlee, the Stardust principal investigator from the University of Washington called finding such high temperature minerals in such a cold part of the solar system “fire and ice.” That’s a pretty apt description.

Among some of the high temperature minerals found in the material returned by Stardust included olivine, a common mineral in the universe and one that makes up much of the green sand beaches found in Hawaii. Scientists, however, were extremely surprised to find it in Comet Wild 2 (“Vilt”). The melting point of olivine is around 1400 K. That’s hot, to say the least

Also found were high temperature minerals rich in calcium, titanium, and aluminum.

How the minerals formed

Scientists are not entirely sure how such an icy body came to be composed of such high temperature minerals but they did offer some possible explanations.

The two possible explanations offered by Brownlee were that the minerals formed here, in our solar system, close to the Sun. It is theorized that they were ejected out of the proto-planetary disk that surrounded the Sun during the birth of the solar system. Once ejected into the outer solar system they became part of the comet. Brownlee said this scenario was “very possible” because several times the mass of the Sun passed through this disk during the formation of the our star system.

The other leading theory is that these minerals formed around other stars, near to the Sun, long ago and were brought into our solar system after they formed around other stars. Likely due forces such as gravity.

The analysis process

The Stardust spacecraft passed by Wild 2 and collected samples in an aerogel (think gelatinous glass) plate. The aerogel plate consisted of 132 cells which were surrounded by aluminum foil and divided into rectangles or in two of the cells trapezoids. Six of these cells have had the comet particles removed and analyzed to determine their make up.

Peter Tsou, JPL’s Deputy Principal Investigator for Stardust, said that when the samples returned there were over 40 particles embedded into the aerogel that were visible to the naked eye.

The particles were removed through a very delicate process, so delicate in fact it partially required the development of new technology. Then they were analyzed for mineralogy, bulk chemistry, isotopes, optical spectrospocy, and organics.

To get at the particles in the aerogel the scientists first had to cut the aerogel, which is far from easy.Comet particle in aerogel. (courtesy JPL, University of California)

Tsou said that scientists first tried to slice it with lasers at varying frequency, that did not work. So the investigators developed a harmonic saw which works similar to a tuning fork by cutting the aerogel through a “vibration cut.” The smallest particles found were about 3 microns across (a human hair is about 1000 microns thick).

The best part of the analysis, in my opinion, is that it is non-destructive. The particle remains intact. This is largely due to 20+ years of research involving stratospheric grains here on Earth. The techniques perfected during that research were applied to the Stardust research.

In addition Stardust collected many interstellar samples along the way which have yet to be looked at because scientists have little to no idea abou how to study these very small, very few particles. But the good thing is that we have these samples here on Earth now and as technology and technique catch up we will be able to go back later and study these particles, which much like the comet particles can give us clues to our own origins. A question that has plagued humanity for eons.

Related Posts:

Stardust

Related Links:

JPL Press Release on conference
University of Washington Press Release on conference
JPL Stardust Web site

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Comments»

1. Brendan Daley - March 12, 2007

I believe that China moved it’s place to space and and some fricken chinese ninjas ate some cheese, but spewed it all up. It collected into a ball of spew cheese and became hard. Jesus was Chinese.


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