Dust particle and its track captured in aerogel by NASA’s Stardust spacecraft in 2004. Credit: NASA
NASA’s Stardust spacecraft did more than snare dust samples of Comet 81P/Wild during its January 2004 flyby. It also caught at least seven fluffy flakes of interstellar dust – microscopic bits of matter exhaled by dying stars that salt and pepper the great open spaces across the Milky Way galaxy. If confirmed, these would be the first grains of matter gathered from outside the sun’s domain.
A team of scientists has been combing through the spacecraft’s aerogel and aluminum foil dust collectors since Stardust returned in 2006. Stardust’s main mission was to collect and return dust from Comet 81P/Wild during its January 2004 flyby, but twice during its 7-year, 3-billion-mile journey, the probe opened up the opposite side of its collectors to gather particles from the direction of the interstellar wind.
A researcher examines dust-collecting aerogel blocks carried by Stardust. Credit: Andrew Westphal, UC Berkeley
As the sun orbits around the center of the Milky Way at 450,000 mph (720,000 kph), material from interstellar space enters the solar system from a particular direction at high speed. Stardust sampled this ‘headwind’ and fortunately snagged a few specks of interstellar dust compared to the more than a million comet particles captured by the other end of the detector.
Artist’s impression of a red giant star blowing out gas and dust. Material lost by aging stars and supernovae may have been captured by NASA’s Stardust mission. Credit: JAXA/ISAS/LIRA
The seven particles probably came from outside our solar system, perhaps created in a supernova explosion millions of years ago and altered by exposure to the extreme space environment. Two of the grains are ‘large’ (1/32,000 of an inch across) and have textures resembling fluffy snowflakes. They contain a magnesium-iron-silicate mineral often found in meteorites called olivine, indicating the material didn’t come from the spacecraft or its collector trays. Dust grains containing these minerals are known to condense in the atmospheres of red giant stars.
This wasn’t scientists’ first encounter with ancient star dust. So-called pre-solar grains, material spewed by previous generations of stars that was gathered by gravity and reworked to form the sun and planets, have been found in very small quantities in meteorites. What Stardust collected are the first contemporary shards of stars blowing across our bow.
Because of their size and number, they’ve been extremely challenging to examine in the laboratory. Scientists caution that additional tests must be done before they can say definitively that these are pieces of debris from interstellar space.
Aerogel’s light and porous structure makes it perfect for capturing fast-moving particles without damaging them. It looks like smoke and feels like Styofoam to the touch. Credit: NASA
Despite barreling in at speeds up to 36,000 mph (54,000 kph), all but one of the particles survived, safely captured by the smoke-like cushion of aerogel. Two were discovered within the aerogel, four had burrowed into the aluminum foil separating the collector trays, and one was traveling so fast it vaporized as it tore through the gel. Three of them contained sulfur compounds, which some astronomers have argued don’t occur in interstellar dust. But who knows?
Supernovas, red giants and other evolved stars produce interstellar dust, water vapor as well as atoms like oxygen and nitrogen and other compounds necessary for life. The two particles captured in the aerogel go by the names Orion and Hylabrook.
Track of the Orion interstellar dust particle in aerogel. Crdit: D. Frank/NASA/JSC
Researchers expected the specks to be little more than formless blobs of material with little structure after being hammered by cosmic radiation, but they were both larger and more complex with their crystal structures intact. They’ll perform further tests to determine the amounts of different forms of oxygen called isotopes within their minerals, which could confirm their interstellar origin.
NASA got help from over 30,000 citizen scientists called “Dusters” in tracking down these particles and many more from the Stardust mission. If you’d like spy some specks yourself – including a shot at potential interstellar crumbs – stop by the Stardust@Home site.