Monday, January 16, 2006

Wild 2's "Cosmic Bootie", Stardust Probe Returns

Update: Video of Stardust's 29,000 mph reentry is here. It sort of became a comet itself!
"Already got scientific results which is great!" -- The very first particle examined is a transparent mineral grain settling discussions about whether comets do indeed contain minerals, glass, etc.

Opportunity!: The interstellar dust (not the comet tail dust) collected in the Stardust Interstellar Dust Collector is extremely small, and only about 45 specimens of interstellar dust (the dust that served as the building blocks for our solar system) are expected to be found in the SIDC's one square foot of aerogel. The collector must be searched with a high magnification microscope with an operator focussing up and down through planes of view, the only way to do this in a timely fashion is to recruit volunteers to search the collector on their home computers.

"The job is roughly equivalent to searching for 45 ants in an entire football field, one 5cm by 5cm (2 inch by 2 inch) square at a time! More than 1.6 million individual fields of view will have to be searched to find the interstellar dust grains. We estimate that it would take more than twenty years of continuous scanning for us to search the entire collector by ourselves.

That is why WE NEED YOU. Volunteers are absolutely critical to the success of this project."

You can pre-register here to help out and if you find an interstellar dust particle, your name goes on the scientific paper announcing its discovery. You'll be a co-author on a very important scientific publication.

(Getty Images)

The Stardust space probe’s capsule, containing samples of dust particles collected from the tail of the comet Wild 2, referred to as "Cosmic Booty" by NASA, returned to earth on Sunday. NASA says that after travelling 2.88 billion miles, collecting samples of the comet’s tail, snapping a few photos, and re-entering the earth’s atmosphere at 29,000 miles per hour (the fastest re-entry ever by a man-made object) the mission is a complete success.

The Stardust space probe was launched seven years ago to make a close fly-by of the comet Wild 2. In 2004 the probe approached to within 150 miles of the comet and returned these stunning images that have changed ideas about the structure of cometary nuclei.

(stereo-image-- look "through" the image so that both sides merge into one 3-D image)

In the case of Wild 2 the nucleus appears to be a solid object rather than a collection of rubble held together by gravity, which was the prevailing view of comet nuclei prior to the Stardust mission. These images also show the presence of impact craters on the comet’s surface in addition to sublimation pits due to the sublimation of ice into gas as the comet is heated during its approach towards the sun.

(NASA, JPL, CalTech)
This sublimation, observed by the Stardust probe as the gas jets released from the comet in the photo above, ejects particles from the comet that follow along behind it and create the comet's tail. Collecting these micrometer sized particles was the main goal of Stardust's mission. A time of flight mass spectrometer aboard the spacecraft analyzed the makeup of 29 particles that were encountered as the probe passed throught the comet's tail. These particles were primarily organic compounds some containing nitrogen and sulfur. Interest in these particles of cometary debris stems from the fact that comets are the left-over material from the formation of our solar system. As Llorca poetically puts it:
"Like a carpentry shop littered with wood shavings after the
work is done, debris left over from the formation of the Sun
and planets is scattered throughout the inner solar system
in the form of asteroids."
As such, they truly are stardust from stars exploded long ago. Analysis of the chemical components of these particles can tell us a great deal about the materials that were present during the earth's formation and can even shed light on the origin of life on this planet by telling us what organic molecules were present and available through bombardment of the earth by comets and asteroids. Among the compounds observed in comets and meteorites are more than 70 different amino acids, at least three of the nitrogenous bases found in RNA, and a variety of 3 to 6 Carbon sugar related molecules.

The presence of these compounds at the formation of the earth, as well as the fact that these compounds are present in objects that continue to strike earth to this day, helps to answer questions about how the first biological macromolecules may have formed on this planet. Indeed, experiments replicating the effects of amino acid containing meteorites impacting the earth has shown that di- and tri-peptides can be formed during such impacts.

Although most comets are similarly ancient in age, Wild 2 is different in many ways than previously studied comets, such as Halley's, in that it only became a resident of the inner solar system about thirty years ago when Jupiter's gravity perturbed its orbit sufficiently to keep it from departing back to the outer reaches of the solar system. Previous to this close encounter with the King of the planets, Wild 2's orbit kept it in the frigid region of the solar system between Jupiter and Uranus, this means that Wild 2 is well-preserved because it hasn't suffered through numerous passages close to the sun which cause comets to sublimate and eject materials from their surfaces. (In many ways it reminds me of fossilized shark's teeth found along the beach in some areas. Teeth that have been washed against the shore are worn have lost definintion and important features. Teeth that have just been washed out of fossil beds are much more intact and show greater definition.) So Wild 2 is a particularly good comet to study because it still retains the composition and structure it had at the time of the solar system's formation. Today, Wild 2's orbit extends from outside the orbit of Jupiter to just inside Mars' orbit, and it complete its own orbit of the sun once every 6.39 years.

The most important part of Stardust's mission was collecting samples of dust particles from Wild 2's tail to return to earth for detailed analysis. These samples were collected in the lightest material on earth Aerogel a microporous material made of silicon dioxide but consisting 99.8% of air. Aerogel's porous nature allows it to slow and capture the particles that collide with it and it has excellent insulating capacity in addition to its light weight.

In addition to the comet dust, Stardust also collected interstellar dust on its way out to rendevous with Wild 2.

Welcome home Stardust! I look forward to seeing what treasures you have brought home from your travels.

The only blog inspired by a bumper sticker.

Comments on "Wild 2's "Cosmic Bootie", Stardust Probe Returns"


Anonymous Anonymous said ... (1/27/2006 5:36 AM) : 

Wonderful explanation of the mission! One thing I've always wondered about comets, though: If they're constantly "shedding" bits of themselves, and getting smacked by meteors and other cosmic debris, won't they eventually wear down to nothingness?


Blogger Dr. Roy Hinkley said ... (1/28/2006 6:16 AM) : 

Thanks Victor.

Yes comets are being worn away by their close approach to the sun. Every trip reduces their size.

"Where comets end

By cosmic standards comets are relatively short-lived. Each time they make a close pass near the sun they lose some of their ice and gas, and after a few hundred trips through the inner solar system all that is left is a loose clump of dust and rocks, the dust and debris of the comet minus the ice and gas that were evaporated away. Some near-Earth asteroids are believed to be the remains of old comets, still following their former orbits but no longer able to put up their dazzling displays. But comets can also end in other ways: Many are broken up by the sun's gravity, some crash directly into the sun. Less often they crash into planets, and though giant planets like Jupiter and Saturn are impacted much more often than Earth, comets are a significant threat to Earth as well. The threat of comet impact was vividly illustrated in 1994 as pieces of Comet Shoemaker-Levy 9 one by one slammed into Jupiter. With thousands of telescopes and several spacecraft watching the comet put on a spectacular display of cosmic fury,"


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