En route to a 2004 rendezvous with the comet Wild 2, NASA’s Stardust probe spent 195 days with its cosmic dust collector, a large tray tiled with silica aerogel, facing the interstellar wind. The hope was that it would snag a few motes of extrasolar dust. Such particles are rare inside the solar system: Intense magnetic fields at the edge of the heliosphere effectively shield us from the smallest grains, but the occasional larger ones—those weighing more than a few femtograms—can barrel through that barrier. During its time spent just outside the Martian orbit, Stardust was bound to encounter some of those particles.
In 2006 the probe’s aerogel tray (shown on the cover) was parachuted back to Earth, where a collaboration led by Andrew Westphal (University of California, Berkeley) and Rhonda Stroud (US Naval Research Laboratory) began to meticulously inspect its contents. With just over one-fourth of the collector’s 1000-cm 2 surface area examined, the researchers now report that they’ve discovered seven grains that likely originated from outside our solar system. 1
“We in the interstellar dust community have been awaiting these results for years,” comments Adolf Witt (University of Toledo, in Ohio). “Up to this point, we’ve essentially had to infer properties of dust indirectly, through astronomical observations. Now they can be examined in the laboratory.” |
