Tiny dust grains may be from interstellar space
Space dust Scientists believe they have captured the first samples of space dust that comes from beyond our solar system.
With the help of citizen scientists, the researchers have identified seven tiny particles of dust that are consistent with interstellar dust, they report in the journal Science.
Dr Andrew Westphal of the University of California Berkley, who led the international team, says the diverse chemical compositions and structures of these potential visitors from beyond our solar system is surprising.
The discovery implies that the space between stars churns and mixes material together from different parts of the galaxy.
The preliminary findings are based on an analysis of microscopic particles collected by NASA's Stardust mission launched in 1999 to collect dust samples from the comet Wild 2 and return them to Earth for study.
"We believe that we have found the first samples of interstellar dust, and it's much more complicated, richer, and far more diverse than we expected," says Westphal.
"For the first time, this lets us get an idea of what interstellar dust is like on a particle by particle basis."
The Stardust spacecraft used giant tiles made out of aerogel and aluminium foil to collect dust samples. Aerogel is an extremely low density lightweight synthetic material, often described as solid smoke.
Westphal and colleagues used the direction of tracks made by particles hitting the aerogel to determine if the dust particles came from interstellar space or from within the solar system.
"Aerogel can give us trajectory information, and these particles were coming from the direction of interstellar dust that's entering our solar system all the time," says Westphal.
The authors admit they will still need to carry out additional tests before they can say definitively that these are samples from interstellar space.
"We only have seven particles at the moment and we are hoping for a lot more as we complete the scanning and analysis," says Westphal.
The researchers say the interstellar particles are fluffy like snowflakes, and far less dense than dust particles originating from within the solar system.
"One of the surprises in the particles that we collected was the discovery of crystalline material rather than the amorphous, glassy silicon based materials detected by astronomical observations," says Westphal.
"The particles containing the crystalline material were gigantic compared to most space dust particles."
Westphal thinks they remained crystalline because their large size allowed them to survive the interstellar conditions that would have turned smaller grains into amorphous material.
So far, the researchers have described three of the particles in detail: Orion, Hylabrook, and Sorok.
"Orion was found at the base of a carrot shaped track and has a mass of about three picograms, a picogram being a trillionth of a gram," says Westphal.
"It consists of olivine or peridot, and spinel, and has an amorphous component and also looks like it has iron in it."
Hylabrook has an olivine core with an amorphous rim and also may contain iron.
"The third particle, Sorok, travelled so fast, it was probably going at more than 20 kilometres per second, any solid material in that particle was vaporised leaving only a gigantic 15 micron diameter track behind," says Westphal.
"The fact that the two largest fluffy particles have crystalline material may imply they came from the atmospheres of stars and were later modified by supernova explosion shockwaves," says Westphal.
The particles were discovered thanks to a citizen science project called stardust@home which involved 30 thousand volunteers patiently scanning through over a million online images of sections of aerogel collector tiles.
"They've done more than 100 million searches so far and found over 100 impact tracks, which would have taken decades for us to do on our own," says Westphal.
Descriptions of the other four particles are the process of being published.
Meanwhile the citizen scientists continue to sift through the data looking for more particles.