Microscopic grains of stardust "shine like a beacon" when scanned by a powerful new instrument, proving for the first time they come from beyond our solar system. Collected by comets and asteroids, the dust ended up in the Earth's stratosphere, where it was collected by NASA and has been scrutinized for decades.
Using a new French instrument called a NanoSIMS ion microprobe, Scott Messenger from Washington University in St. Louis and his colleagues were able to pick out the specks of star matter from the black sprinkles of dust. The instrument ferreted out the tiniest molecules of stellar sand and glass, which carried a form of oxygen foreign to the solar system. These oxygen isotopes -- carrying a different number of neutrons from native oxygen -- light up under the scanner, which was set to identify these particular isotopes, Messenger said.
"It's shining like a little beacon," said Messenger, whose work is reported in Friday's issue of Science. "They are these little glass balls that are shot full of little beads of iron, nickel, metal and iron sulfides," Messenger added.
"A colleague of ours has been looking at these things for years and found a lot of intriguing similarities with what astronomers think interstellar grains should look like.
"Something like 40,000 metric tons per year of this stuff is falling on Earth," Messenger said. It is believed to come from the tails of comets and from asteroids, which collected the dust as they spiraled into the sun.