NASA has identified for the first time seven rare, microscopic interstellar dust particles — that date to the beginnings of the solar system. The particles have been identified amongst samples obtained by NASA's Stardust spacecraft, which returned to Earth back in 2006.
The craft contained a tray of silica aerogel, which captured small interstellar dust particles as it journeyed through space on a seven-year, 4.8 billion kilometre journey.
Why's it taken so long to find the new particles? Well, these things are small. Very, very small. NASA explains how it was done:
Two particles, each only about two microns (thousandths of a millimetre) in diameter, were isolated after their tracks were discovered by a group of citizen scientists. These volunteers, who call themselves "Dusters," scanned more than a million images as part of a University of California, Berkeley, citizen-science project, which proved critical to finding these needles in a haystack.
A third track, following the direction of the wind during flight, was left by a particle that apparently was moving so fast — more than 10 miles per second (15 kilometers per second) — that it vaporized. Volunteers identified tracks left by another 29 particles that were determined to have been kicked out of the spacecraft into the collectors.
Four of the particles reported in Science were found in aluminium foils between tiles on the collector tray. Although the foils were not originally planned as dust collection surfaces, an international team led by physicist Rhonda Stroud of the Naval Research Laboratory searched the foils and identified four pits lined with material composed of elements that fit the profile of interstellar dust particles.
The chemical composition of these particles varies quite a lot, with the smaller ones distinct from the larger ones, so they appear to have varying histories. Some also contain sulfur, though, and some scientists argue that the element shouldn't be present in interstellar dust.
So, what awaits the particles is further inspection, before NASA can definitively say that the debris can help explain the origin and evolution of interstellar dust. Let's wait and see. [NASA]