NASA's Stardust spacecraft launched in 1999. Its mission was simple enough: Travel through space collecting interstellar dust particles. The vehicle headed towards Jupiter to collect and return comet samples. NASA scientists have been analyzing the payload since its return to Earth back in 2006. After careful analysis, the team has detected the first potential contemporary interstellar dust particles. These particles could date back to the formation of our solar system and, if confirmed, would be an incredible discovery.
The Stardust spacecraft encountered multiple comets on its seven year mission, and it returned to the Utah Testing and Training Range in 2006. The vehicle's Sample Return Canister was transferred to a holding facility at Johnson Space Center where it has been kept for analysis. The Sample Return Canister is composed of a tennis-racket-shaped collection tray, with one half used to collect samples from comets and the other half used for interstellar collections. In 2004, the vehicle flew along a comet, gathering particles and locking them in a silica aerogel for storage. Upon return, the samples have been meticulously scrutinized and scientists have identified seven distinct particles that could have extrasolar origins. These particles may even have been forged in a supernova explosion, and altered by the harsh environment of outer space.
“These are the most challenging objects we will ever have in the lab for study, and it is a triumph that we have made as much progress in their analysis as we have,” said Michael Zolensky, curator of the Stardust laboratory at NASA’s Johnson Space Center in Houston and coauthor of the Science paper.
After careful analysis, scientists were surprised to discover the particles have a more diverse structure and chemical composition that originally predicted. There were different sizes of particles, each with a different history. The team noted that the larger, more massive particles were "fluffy" in nature, very similar to a snowflake. More detailed analysis is needed to determine if these particles truly come from outside of the solar system. If so, they will be able to answer many questions scientist currently have about how interstellar dust forms and also how it evolves over time.
Four of the seven particles identified were not discovered in the aerogel, but in the aluminum foils between the collection trays. Although the foils were not originally designed as collection receptacles, the foils proved very beneficial. Three of these four particles are only a few tenths of a micro thick and are composed of sulfuric compounds -- compounds that are currently not associated with interstellar dust. Future analysis will be able to identify a larger sample of these particles to truly understand their origins.
With the help of some "Dusters", a group of citizen scientists, two particles approximately two microns (mere thousandths of a millimeter) thick were isolated after their tracks and identified. The University of California Berkley volunteer group scanned over one million images in search of these particles. A third track was discovered, thought to be left behind by a particle moving so fast (approximately 15 kilometers per second), that it vaporized upon impact with the receptacle. Additionally, the volunteers have identified 29 other particles.
So far, Johnson scientists have scanned half of Stardust's collection panels at varying depths. The scans were then converted into video format and posted online for the Dusters to access and evaluate. If a particle is identified, the Duster tags the track and a team of scientists led by Andrew Westphal verifies the identifications. Of the one million framed scanned so far (each around half a millimeter square), the Dusters have identified 69 tracks with two of those verified by Westphal's team. The team has named two of the particles Orion and Hylabrook. This dusty duo is will be studied in great detail in hopes of determining their oxygen isotope quantities and verifying their extrasolar origins.