From 1999 until 2006, NASA’s Stardust spacecraft traveled three billion miles acting as a sort of vacuum cleaner in space. It collected tiny bits of dust just a few thousandths of a millimeter across, or about one-fifteenth the width of a human hair.

While there are many things within our solar system that produce dust and debris, interstellar dust is produced by supernovas, red giants and other evolved stars. These stars generate heavy elements such as oxygen, nitrogen and carbon which are necessary for life.

Over the eight years since Startust returned, NASA researchers and volunteers with the Stardust@home citizen science project have been examining the bits of dust, looking for signs that they may have come from outside our solar system.

To date about two-thirds of the dust collecting panels have been examined, and researchers believe that they have found seven particles of interstellar dust. This represents roughly one particle per million collected.

The researchers indicate that the motes found are much more diverse in terms of structure and composition than had been expected. The large particles are much different than the small ones and may have a different history.

“The fact that the two largest fluffy particles have crystalline material – a magnesium-iron-silicate mineral called olivine – may imply that these are particles that came from the disks around other stars and were modified in the interstellar medium. We seem to be getting our first glimpse of the surprising diversity of interstellar dust particles, which is impossible to explore through astronomical observations alone,” said Andrew Westphal, a physicist at the University of California, Berkeley’s Space Sciences Laboratory in a statement.

Westphal is the lead author of a paper which will appear in the August 15th issue of the journal Science. A dozen additional papers on the subject are now online and will appear in the journal Meteoritics & Planetary Science.e (MAPS).

Two particles were found by volunteers with the Stardust@home project, who call themselves ‘Dusters.’ Stardust@home is a citizen science project run by UC Berkeley. Once several Dusters flagged a likely sample, the specimens were vetted by Westphal’s team.

A total of 31 samples were extracted by scientists at Johnson Space Center and shipped to UC Berkeley to be analyzed by a scanning transmission x-ray microscope, or STXM, attached to a synchrotron beam line at the Advanced Light Source at Lawrence Berkeley National Laboratory.

“As one of the first citizen-science projects, Stardust@home has been an amazing success. If we had had one person searching the aerogel 40 hours per week, they would have taken three years to cover once the same area searched multiple times by the Dusters,” said said UC Berkeley research physicist Anna Butterworth, who is first author of one of the 12 MAPS papers about the project.

Two of the particles, dubbed Orion and Hylabrook by their Duster discoverers and paper coauthors, will be subjected to additional tests to determine their oxygen isotope abundances. This could provide additional evidence of an extra-solar origin.

Four of the particles found were in aluminum foils located between tiles on the collector tray. The foils were not intended as a collection surface, however an international team led by physicist and nanoastronomer Rhonda Stroud of the Naval Research Laboratory searched the aluminum for the smallest particles that might be captured. These were found at the bottom of microscopic pits in the foil.

“They were splatted a bit, but the majority of the particles were still there at the bottom of the crater. Their diversity was a surprise, but also these fluffy particles, sort of like a tossed salad, were complex, an agglomeration of other particles, rather than one dense particle suggested by the simplest models of interstellar particles,” said Stroud.

Three of the particles contained sulfur compounds which were previously believed not to exist in interstellar dust.

A sizable portion of the samples collected by Stardust have yet to be analyzed. When all of the sorting and analysis is complete, Westphal expects to find no more than a dozen particles of interstellar dust. He has also emphasized that additional tests are required to determine whether or not the seven current specimens originated outside this solar system.

However, even a small amount of interstellar dust could help to provide answers about the origin and evolution of interstellar dust.