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First samples of dust from outside the solar system

The first microscopic particles likely from interstellar space have been identified from the same Stardust spacecraft that sampled a comet’s tail.

Dust streaming into the solar system from interstellar space was caught in special collectors on the side of the Stardust spacecraft that faced away from the comet. The samples then came back to Earth when the probe returned in 2006.

After long searching and careful analysis of a handful of microscopic particles by scientists in laboratories across the world, including Anton Kearsley and Dr Ashley King, both from the Natural History Museum, seven grains have been identified as likely originating outside our solar system.

If confirmed, the particles would give the first evidence of the origins and evolution of interstellar dust, which could only previously be guessed at with astronomical observations.

'We can now glimpse the structure and composition of the very tiny grains that astronomers detect from afar,' said Kearsley.

People power

In order to search for the extremely small interstellar particles (many less than a thousandth of a millimetre across, and weighing little more than one millionth of a millionth of a millionth of a gram), researchers from the University of California at Berkeley turned to the public for help.

More than 30,000 people worldwide (who are all listed as co-authors on the new research paper) scoured over a million digital microscope images of the collector’s surface for tracks caused by dust particles crashing into aerogel, an ultralight material nicknamed 'frozen smoke'.

The researchers also studied the aluminium surfaces between the aerogel panels, looking for tiny craters. In total, more than 70 impacts were identified. The majority of those analysed contained flecks of the aluminium or bits of solar cells blown off the spacecraft, but seven tracks and craters yielded particles likely to be interstellar dust.

Interstellar surprises

The identified particles are already producing surprises. They are fewer in number, but more diverse than predicted, with differing chemical compositions between relatively small particles and larger ones that probably had a 'fluffy structure like a snowflake,' according to lead author Dr Andrew Westphal, from the University of California at Berkeley.

Some of the particles also contained quite a lot of sulphur, which some astronomers had predicted would not be found in the dust, having been lost to interstellar gas. Further tests on the particles to discover more about their nature and origins and evolution, as well as more searching of the aerogel panels for additional particles, are ongoing.

There's still time to get your name on the next paper by joining Stardust@Home and becoming a ‘duster’, scouring images for tiny tracks of interstellar dust.