In 1999, scientists launched the Stardust spacecraft with two missions: collect samples from Comet Wild-2, and collect free-floating interstellar dust inside of a vaporous aerogel membrane. Now, 15 years later and with considerable volunteer help, we have seven confirmed stardust impacts—and two preserved grains of interstellar dust—to show for it. And while this may not sound like very much, it's a pretty big deal.
You can see some impressive visuals from the mission—and the Wild-2 flyby (at that proximity, it pretty much just looks like a massive, battered rock)—in this 31-second video:
So what are we going to do with two grains of stardust? Well, for starters they may give us a sense of how interstellar dust is shaped and altered during transit. Scientists have created complex fractal adhesion models to account for the convoluted shape of stardust we might reasonably expect, given their environment, but we don't really have any way of knowing whether these models are useful until we've studied actual fragments of interstellar dust.
Having physical specimens of interstellar dust in our possession can also be useful when we're evaluating the Planck satellite's dust map, which studies the composition of interstellar dust and the microwave radiation they emit. And as we develop new technologies with which to study interstellar dust, these samples may tell us more than current technology can. And it's not just the surviving grains that tell a story. The other five impacts—especially the four dust residue marks on the aerogel's aluminum shielding—may also tell us more about the chemical composition of the mysterious interstellar clouds that swirl around us.