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Seven specks of stardust from outside the solar system have been brought back to Earth for the first time.

These tiny grains, some of which are a millionth of a millionth of a gram, could help scientists explain how solar systems form.

Scientists believe they were created in a supernova explosion millions of years ago and altered by eons of exposure to the extremes of space. 

The largest interstellar dust track found in the Stardust spacecraft collectors was this 35 micron-long hole produced by a tiny speck of stardust that was probably travelling so fast that it vaporised upon impact

'No one has caught stuff from outside the solar system and returned it to Earth before,' Anton Kearsley, microanalyst at the Natural History Museum told MailOnline.

Their tiny size, meant they took six years to find. 'For perspective, you can fit a billion of these in a grain of sand,' he said.

Interstellar dust thrown out by exploding stars is believed to scatter the heavy elements necessary for life - such as carbon, nitrogen and oxygen - across the galaxy.

After a life cycle of millions of years, the dust can lead to planetary formation and acts as a key component in the evolution of the galaxy, researchers claim.

The left image shows on the interstellar dust impacts in the foil aboard the Stardust spacecraft. The crater is about 280 nanometres across; 400 of these craters would span the width of a human hair. The right image shows one of the specs of stardust with crystalline mineral olivine (pink), made from magnesium

In this sense, everyone on Earth is partly made from stardust.

'They are very precious particles,' said lead researcher Dr Andrew Westphal, from the University of California at Berkeley.

'Fundamentally, the solar system and everything in it was ultimately derived from a cloud of interstellar gas and dust.

'We're looking at material that's very similar to what made our solar system.'

These particles, collected by the Stardust spacecraft, are much more diverse in terms of chemical composition and structure than first thought.

For instance, some of the larger ones had a snowflake-like 'fluffy' structure, said the researchers, writing in the journal Science.

'The fact that the two largest fluffy particles have crystalline material - a magnesium-iron-silicate mineral called olivine - may imply that these are particles that came from the disks around other stars and were modified in the interstellar medium,' said Dr Westphal.

'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.'

Nasa's Stardust spacecraft (artist's impression pictured) was launched in 1999 to fly through the coma - the envelope of gas and dust - surrounding comet Wild-2. Using a 'fly paper' technique, it was designed to catch cometary dust in tiles of soft aerogel separated by pieces of aluminium foil

Mr Kearsley said knowing what the dust is made from, and its structure, could will help understand some of the fundamental mysteries of how dust and gas lead to star and planet formation.

'Our solar system is ramming its way through interstellar space. As it's going, it collecting these grains,' said Mr Kearsley.

'For me, the most interesting thing is that some of these little grains may tell us whether any of the dust we are seeing came directly from supernova explosions outside our solar system,' Mr Kearsley told MailOnline. 

'Knowing the structure and composition of the particle will help us calculate the temperatures of giant dust clouds.

This is important because it lets you know what kinds of reactions go inside them – how they evolve, collapse, and how solar systems can form.'

Nasa's Stardust spacecraft was launched in 1999 to fly through the coma - the envelope of gas and dust - surrounding comet Wild-2.

Using a 'fly paper' technique, it was designed to catch cometary dust in tiles of soft aerogel separated by pieces of aluminium foil.

A similar collector was placed on the rear of the probe to collect particles from streams of interstellar dust flowing through the galaxy.

Both collectors were dropped by parachute and recovered after Stardust returned to Earth in 2006.

Volunteers with home computers, who called themselves 'dusters', were invited to help the professionals scan more than a million dust-track images.

The citizen science project, dubbed Stardust@home, proved critical to the needle-in-a-haystack search.

Dust grains that form around dying stars and are thrown out into the cosmos can lead to the formation of planets and are a key component of the universe's evolution. Stars are pictured here in the Orion Nebula

Scientists identified just seven particles that were likely to have had an interstellar origin.

Three either lodged or left traces within the aerogel while the remains of four others were found in pits in the aluminium foil.

These particles were a tenth of the size of comet dust, measuring up to two thousandths of a millimetre across, and varied in composition.

Three particles from in the search contained sulphur compounds which some astronomers argue should not be found in interstellar dust.

Describing the dust residues discovered in the foil, Dr Rhonda Stroud from the US Naval Research Laboratory said: 'They were splatted a bit but the majority of the particles were still there at the bottom of the crater.

'Their diversity was a surprise, but also these fluffy particles, sort of like a tossed salad, were complex, an agglomeration of other particles, rather than one dense particle suggested by the simplest models of interstellar particles.'

'The key thing is this is just the start,' said Mr Kearsley. 'We didn't really know for certain we were going to find this material…it really is breaking completely new ground.'