Stardust, a spacecraft launched in 1999 to gather dust from the comet Wild 2 has collected seven particles that could have traveled from outside the Solar System. The vehicle launched an aerogel pack containing the dust back to Earth in 2006. Since that time, researchers have examined the celestial partiles collected during the mission.
Andrew Westphal, physicist at the Space Sciences Laboratory at the University of California, Berkeley, believes these tiny dust flakes may have formed in the massive blast of a supernova explosion millions of years in the past. In addition to particles and dust from the comet and these rouge visitors, scientists have already discovered at least 50 particles cast off from the spacecraft itself. These were identified by their chemical makeup and trajectory through the gel.
Particles studied from the return mission included flecks of all different sizes, and shapes. The largest of these exhibited structures much like snowflakes, containing the mineral olivine. This suggests to researchers that the particles may have formed around other stars, later becoming exposed to the interstellar medium - the region between stars.
Alien dust was predicted to gather dust and other particles which had formed around other stars - that is how the mission earned its name. These particles were collected by both the aerogel collector - a super-lightweight material manufactured from gel and gas - as well as aluminum foil dust collectors. Stardust was predicted to gather just one particle of interstellar dust, heading near Earth, for every million particles it collected from the comet.
Interstellar dust was identified, in part, through the Stardust@Home project, which assisted amateur scientists in identifying candidate tracks. More than one million images, created from the sample return, were examined by the volunteer team of "dusters."
Citizen scientists found a pair of candidate tracks in their search for interstellar dust. They also discovered a track which appeared to be from the direction of the interstellar medium, but no particle was found. It is possible that the fleck which created this mark entered the aerogel with so much force that it vaporized. Dusters for Stardust@Home also contributed to the project by finding 29 tracks left by spacecraft debris.
Three of these seven particles contain sulfur compounds which could suggest they are not from interstellar space, challenging the current findings.
Interstellar dust is likely to be found as study continues on the Stardust return package. Just 77 of the 132 total aerogel panels have been scanned for examination so far, and 100 potential tracks remain to be investigated from the original group.
Discovery of the seven potentially interstellar dust particles was announced in the journal Science.
