Seven dust specks captured by a NASA probe likely came from the vast expanse of space beyond our solar system’s boundaries.
The particles are "primordial material unaltered by the violent birth of the solar system," reports Science’s Richard A. Kerr. The Stardust spacecraft gathered the dust as it swung by Comet Wild-2 in 2004. Two years later it delivered the gathered material to Earth via parachute. This month, researchers published the first analysis of the samples.
All the seven particles all have distinct compositions — some are rather fluffy and have a mineral called olivine, which is called peridot when it is a gem. Others are silicon- and carbon-rich.
A waffle-textured plate scooped up dust specks during the mission. Most of the plate contained a special material called aerogel that's able to nab particles moving rapidly through space and slow them down without damage. The rest of the plate was covered with aluminum foil. When dust particles hit that foil, they leave a residue that scientists can analyze.
After traveling through space, the aerogel returned to Earth full of streaks. To find tracks with dust specks at the end, scientists called on volunteers to screen over 700,000 images through the citizen science project Stardust@Home. Out of 71 tracks the volunteers found, the scientists determined that three were traced by dust that likely came from outside our solar system. Four other particles that hit the aluminum foil also made it into the recent paper.
The researchers need to do a few more tests to make sure the particles are truly of interstellar origin. The task is difficult with only seven precious particles, but more could be found: The Stardust@Home volunteers have found 100 additional tracks that have yet to be analyzed.