NASA’s Stardust probe reveals first dust grains from beyond our solar system

This artist's impression shows the dust forming around a supernova after the explosive death of a star. Astronomers using the European Southern Observatory's Very Large Telescope have found that dust grains form in a two-stage process. (ESO/M. Kornmesser)

They may be microscopic in size, but little grains of dust scooped up in deep space by NASA’s Stardust spacecraft may be some of the most precious samples from the cosmos ever collected.

Astronomers announced this week that we may for the first time actually have in our hands visitors from beyond our solar system in the form of interstellar dust.

After launching in 1999 and completing a roundabout journey through the solar system, including swinging by a comet, the plucky probe stuck out its tennis-racket sized collector panels in the hopes of capturing some of these elusive particles.

Now eight years after its return to Earth with its precious cargo, the spacecraft’s aerogel collecting panels have been thoroughly combed through, and have indeed finally revealed its treasures in the form of a handful of infinitesimal particles lodged within the centimetre-thick gel.

Until now, however, astronomers have only been able to base their ideas of what interstellar dust might look like through blurry telescope views.

Now all that changes, say the authors of the study published this week in the journal Science.

“Our only information about interstellar dust has [until now] come from astronomical observations so we couldn't know what we might find,” said study co-author Anna Butterworth, a planetary science researcher with the University of California at Berkeley in an interview with Yahoo Canada News.

“Being able to analyze a microscopic piece of dust, much as a geologist would analyze a rock, opens up new possibilities of testing astronomers models with laboratory measurements.”

Before being captured, these motes of dust had been streaming through space at speeds of over 15,000 km per hour.

In fact, our Milky Way is thought be a pretty dusty place, with particles continually produced thanks to stars exploding, and asteroids and comets colliding and shedding material.

Astronomers believe that as our solar system plows through our galaxy, it is continually pelted by a ‘snowstorm’ of dust that fills interstellar space – the void between the stars.

And it turns out that part of what clued researchers in on their origins was the direction they appeared to be flying in from.

“The team found that the Interstellar dust particles appear to come from one direction because of the movement of our solar system through the galaxy, rather like snowflakes hitting your windshield driving through a snowstorm,” Butterworth said.

The team had found dozens of tracks and particles embedded in the gel and aluminium panels but were able to pin down most of their origins as coming from our own solar system.

“Most impacts in the collectors were from the spacecraft where some solar system object hit and knocked off a small piece of debris,” Butterworth explained.

“We could detect these impacts of aluminum metal and solar panel glass quite easily using X-ray chemical analysis, and rule them out as candidates.”

While there are still more tests to be done to absolutely confirm origins of their cosmic catch, examinations so far reveal that seven – yes, only seven – embedded grains are structurally and chemically different than anything researchers have ever seen before.

Crystalline structures have been found in some of the samples that indicate they may have originated in a hot environment, Butterworth says, like what we expect in dusty disks that commonly encircle distant stars.

Some of the larger snowflake-like particles – weighing no more than a few trillionth of a gram – have the telltale chemical signatures that point to them being forged in a supernova explosion a few million years ago.

At this point Butterworth and her team will have to assess their isotopic fingerprints to see if they make a match with the chemistry found in supernovae, but the team is optimistic.

If it turns out these minuscule specks are in fact ashes of a star blast and debris from stellar disk, it may be our first direct glimpse into the surprising diversity of our own galactic neighbourhood.

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