Detectors dropped off by the Stardust probe in 2006 carried
particles that may have originated in interstellar space.
Ian Sample, science editor
The Guardian,
Thursday 14 August 2014 14.01 EDT
A technician unbolts a canister containing cometary and
interstellar dust from the Stardust capsule.
It could be the most exotic material on the planet. Seven
particles of dust brought back to Earth by a spacecraft nearly a decade ago
appear to have come from beyond our solar system.
The specks have all the hallmarks of being created in
interstellar space. If confirmed, it would make them the first material from
outside the solar system to be brought to Earth for study.
Scientists found the tiny particles – including some shaped
like fluffy snowflakes – on detectors carried by Nasa's Stardust probe which
launched in 1999 on a mission to capture dust from interstellar space and the
tail of comet Wild-2.
The detectors were dropped to Earth by parachute when
Stardust flew past in 2006. Each detector worked like cosmic fly-paper and
collected particles as they hurtled past the spacecraft.
An optical microscope image of a track through aerogel made
by Orion, one of the dust particles believed to be from interstellar space.
The dust might have been created in a supernova explosion
millions of years ago and shaped by their exposure to the harsh extremes of
space. "These are very precious particles," said Andrew Westphal, a
physicist at the University of California in Berkeley, who worked on the dust.
The two largest fluffy particles contain a crystalline
magnesium-iron-silicate mineral called olivine, which suggested that they came
from the discs around stars and were altered by the interstellar environment,
Westphal said.
If the nature of the dust is confirmed, then studies of the
material could shed light on the origins of interstellar dust. Almost
everything known about interstellar dust has come from observations, either
with ground-based or space-based telescopes. "We seem to be getting our
first glimpse of the surprising diversity of interstellar dust particles, which
is impossible to explore through astronomical observations alone,"
Westphal added.
The international team of scientists sought help from more
than 30,000 citizen scientists to scan thousands of microscope images in search
of the particles. The largest of the particles was only a few thousandths of a
millimetre across, considerably smaller than this full stop. Most of the specks
weighed a few millionths of a millionth of a gram.
Two particles, named Orion and Hylabrook by their
discoverers, were found from the tracks they left in detectors made from
aerogel, an ultra-light and porous material. Scientists found a third track
from a particle moving in the same direction, but it was evidently moving so
fast, at more than 15km per second, that it vapourised on impact.
Four more particles, with the right chemical make-up for
interstellar dust, were found at the bottom of pits left in thin aluminium
foils built into the detectors. "They were splattered a bit, but the
majority of the particles were still there at the bottom of the crater,"
said Rhonda Stroud at the Naval Research Laboratory in Washington DC. More
tests are planned on the particles to confirm or rule out their interstellar
origins.
Besides the exotic dust particles, researchers identified
more than 50 other particles of spacecraft debris in the Stardust detectors,
according to a report in Science.
Anton Kearsley, a microanalyst who took part in the study at
the Natural History Museum in London, said recognising interstellar dust was a
huge challenge.
"In the end, 30,000 people around the world worked
through thousands of digital microscope images of the main part of the
collector, the aerogel, and eventually found the tracks that included
interstellar dust particles," he said.
"As the results came in, the numbers and sizes of dust
grains were not what we'd expected, and many seemed to have come from strange
directions," he added. "Only by careful plotting of impact directions
was the team able to identify the seven particles that must have come from
outside the solar system."
No comments:
Post a Comment