Definition of finding a needle in a haystack? 100 million searches by over 30,000 people to find seven “probable” interstellar dust particles in debris collected by NASA’s Stardust spacecraft. These minute motes are not of this solar system but alien dust from intergalactic space.
The discoveries top a 7-plus year search by the Stardust team and thousands of volunteers to track down samples of the primordial dust wafting through interstellar space – the same stuff that long ago congealed to form the sun and planets.
I should be careful of my terms. These bits of cosmic debri, a thousandth the mass of comet dust, tear across space at nearly 10,000 mph (15,000 km/hr). They’re also incredibly sparse. Catching even one requires VERY delicate handling and a bit of luck.
Scientists used one of the most bizarre substances ever invented to grab the speedy dust particles without damaging them: aerogel. Sometimes called “frozen smoke”, aerogel is a pale blue, airy substance made of 99.8% empty space webbed with silica. Particles traveling thousands of miles an hour can safely speed through aerogel until they slow down and bury themselves within its porous, sponge-like texture. A high tech butterfly net as it were.
The Stardust spacecraft, launched in 1999, accomplished its main objective of collecting dust particles from the misty atmosphere or coma of comet Wild 2 and returning them in a reentry capsule when the probe passed by Earth in 2006.
That’s not all. For a total of 200 days in 2000 and 2002, Stardust stuck out its tennis racket-sized collector tray to snatch bits of interstellar dust that sifts across the solar system as the sun and planets orbit the galaxy at 4.3 miles per second.
Problem was, there were so many pieces of aerogel to examine for tracks and possible particles, the Stardust team knew it would take ages unless they got help. So they went public and set up the Stardust@home website.
Regular folks like you and I were offered (and still have) the opportunity to examine microscopic images of aerogel slices on our computers and look for tracks left by debris from alien stars and Milky Way gas clouds. 30,714 people signed up, and after years of work doing one of the things humans do best – recognize patterns – seven possible candidates were found.
Two particles weighed in at just three trillionths of a gram; another came in so fast it left only a bit of residue. Four missed the aerogel but blasted microscopic craters in the surrounding aluminum foil, leaving traces of vaporized debris within the craters.
To confirm that the specks are truly from beyond the planets, researchers must now transfer them from the aerogel to instruments for close examination. They’re so incredibly small, great care must be taken not to lose the precious pieces.
If you’d like to learn more and become a “duster” yourself, the name given to those teasing tracks from photos, click over to Stardust@home. Bruce Hudson of Ontario, Canada discovered the first particle and was given the privilege of naming it. He chose “Orion”, and it’s featured in the photo at the top of this article.