Now, after several years of lab work with the particles, scientists say Stardust likely captured interstellar particles -- dust from outside our solar system.
The probe caught the dust using its tennis racket-like arm, which it held out as it drifted through space. The racket's string-like grid of aluminum cells was filled with particle-catching aerogel, a silica-based foam as light as air. The gel was ideal for capturing space dust without damaging the delicate particles. The only problem: NASA engineers designed and launched the probe without a plan to get the dust particles out.
Ultimately, engineers decided the best strategy was to not try to remove them at all. Instead, they scanned the gel with an automated microscope and then had hundreds of volunteer citizen scientists help them analyze the data to find the different particles' imprints.
Andrew Westphal, who lead the research at the Space Sciences Laboratory at the University of California, Berkeley, said he and his colleagues -- including several hundred online volunteers -- located 31 different footprints or tracks of tiny cosmic dust particles. "All of the indications point to an interstellar origin," Westphal claimed.
"We've thought hard about alternative explanations for where these grains came from," he told National Geographic, but says somewhere out in between distant stars is the best explanation.
Westphal's work is detailed in the latest edition of the journal Science. The 714 amateur scientists that helped Westphal and his Berkeley colleagues locate the dust are listed as co-authors.