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Scientists now believe that the spacecraft Stardust captured seven particles from interstellar space during its seven year journey.
Inside the canister, a tennis racket-like sample collector tray captured the particles in silica aerogel as the spacecraft flew within 149 miles (about 240 kilometers) of a comet in January 2004. An opposite side of the tray holds interstellar dust particles captured by the spacecraft during its seven-year, three-billion-mile journey.
Scientists caution that additional tests must be done before they can say definitively that these are pieces of debris from interstellar space. But if they are, the particles could help explain the origin and evolution of interstellar dust. The particles are much more diverse in terms of chemical composition and structure than scientists expected. The smaller particles differ greatly from the larger ones and appear to have varying histories. Many of the larger particles have been described as having a fluffy structure, similar to a snowflake. [emphasis mine]
It appears that for these seven particles, the scientists conclude they are likely interstellar particles because of the speed in which they were traveling when captured as well as their make-up. Both suggest an origin outside the solar system.
However, we should be cautious about this. The data still remains tenuous and preliminary. More work obviously needs to be done to pin this down definitively. More information here.