First Interstellar Dust Brought Back to Earth
Fifteen years ago, the Stardust spacecraft blasted off from Cape Canaveral with the goal of collecting the tiny particles adrift in the ocean of space: cosmic dust.
In 2000 and 2002, Stardust opened its aerogel collectors wide in the hopes of catching some of that dust. Two years later, the spacecraft encountered the comet Wild 2 and began tailing the object like a bicyclist drafting a competitor. With its collectors open once again, the spacecraft basked in the nebulous coma of the comet, aiming to catch any particles shedding away.
When Stardust passed by Earth in 2006, the vessel dropped off a precious package, a capsule containing the aerogel collectors, hopefully plastered with dust particles from beyond our solar system. "Dropped" is a bit of an understatement. The capsule plummeted through Earth's atmosphere at a velocity of 12.9 kilometers per second, the fastest reentry speed ever achieved by a man-made object. Peak deceleration was measured at 34 gs. Luckily, the collectors were packed nice and tight; they were just fine. NASA scientists took them to a specially designed clean room to minimize contamination and found a million microscopic specks of dust embedded in the aerogel. A tad overwhelmed, they opened up the process of analyzing the specks to citizen scientists via Stardust@Home. Naming themselves "Dusters," the volunteers scanned magnified images to identify trails in the aerogel much thinner than a human hair. Once the trails were identified, NASA scientists extracted and analyzed them.
Today, after eight years, the Stardust team has officially announced in the journal Science that seven of those one million tiny specks are -- very probably -- interstellar dust.
The seven particles, all on the picogram scale (one-trillionth of a gram!) are incredibly diverse. One, named "Sorok," is composed of magnesium and iron-rich silicates. Two others, "Hylabrook" and "Orion," sport an olivine core surrounded by other trace elements like silicon and manganese. The larger pieces are fluffy like snowflakes, lead author and UC-Berkeley physicist Andrew Westphal said.
Additional tests are underway that will further confirm that the particles are of interstellar origin.
The universe is in a constant state of recycling, and cosmic dust allows us to trace the process. Often exploded from supernovae or exuded from waning red giant stars, dust particles can later join together to form new planets and stars.
Besides allowing us to characterize the properties of interstellar dust, NASA believes that the miniscule grains described today could help reveal the secrets of the stars and elucidate the creation of chemical elements.
Source: Westphal et. al. "Evidence for interstellar origin of seven dust particles collected by the Stardust spacecraft." Science. 15 Aug 2014. VOL 345 ISSUE 6198
(Images: NASA, Anna Butterworth)