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It has long been thought that asteroids formed from planetary embryos known as protoplanets that eventually combined and led to the formation of fully-fledged planets.

But, now a study claims that asteroids are not building blocks at all - but rather they were made from the collisions of these protoplanets.

If true, the research would mean that meteorites on Earth are not a glimpse into a time before Earth was formed, and are instead merely a byproduct of our own planet's formation.  

Scientists at Purdue University in Louisiana have presented a new asteroid theory. They say asteroids may have formed during the collision of protoplanets (illustration shown). Such planetary embryos combined to create the terrestrial planets. Previously it was thought asteroids formed before the protoplanets

The new theory centres around tiny, glassy, spherical grains known as chondrules. These were once molten droplets, and are now found scattered over asteroids.

It had been thought that chondrules were the early kernels of terrestrial planets. As the solar system started to pull together four billion years ago, these droplets collided with dust and gas, creating the early protoplanets.

These were objects larger than an asteroid, but smaller than our moon in size, and they ultimately formed the terrestrial planets in the inner solar system today.

The scientists at Purdue University in Indiana, who carried out the latest research, however, say that chondrules actually formed after the protoplanets.

They claim that when protoplanets in the early solar system collided, creating the planets, the collisions created asteroids as a byproduct.

These bodies would have smashed together with such violent force that they melted a fraction of their material, and shot a molten plume out into the surrounding solar nebula.

Droplets of this molten material would have eventually cooled to form chondrules, which in turn attached to larger bodies like asteroids - some of which would eventually impact Earth, to be preserved as meteorites.

Dr Brandon Johnson, now a postdoctoral researcher at the Massachusetts Institute of Technology, told MailOnline that this new theory would apply to the more than 90 per cent of meteorites that contain abundant chondrules.

Others that contain no chondrules 'are likely more representative of the material that accreted to form planetesimals or planetary building blocks,' he added. 

The new research is based on an analysis of how chondrules formed. These tiny, glassy, spherical grains - the circular objects on the meteorite seen here - are now thought to have formed in the collision of protoplanets in the early solar system, suggesting asteroids also formed around a similar time

Bodies in the solar nebula around the young sun (illustration shown) would have smashed together with such violent force that they melted a fraction of their material, and shot a molten plume out. Droplets of this molten material would have eventually cooled to form chondrules, which attached to larger bodies like asteroids

'Chondrule-bearing meteorites have long been thought to be similar to the building blocks of planets,' said Dr David Minton, an assistant professor of Earth, atmospheric and planetary science at Purdue, who was involved in the research.

'This study suggests that instead chondrules might actually be byproducts of impacts between objects of an earlier generation, and meteorites may not be representative of the material that made planets.'

His colleague Dr Jay Melosh, a professor in the same department, added: 'Understanding the origin of chondrules is like looking through the keyhole of a door; while we can't see all that is happening behind the door, it gives us a clear view of one part of the room and a glimpse into the very beginnings of our solar system.

'We've found that an impact model fits extremely well with what we know about this unique material and the early solar system, and this suggests that, contrary to the current opinion among meteorite experts, asteroids are not leftover planet-building material and clumps of chondrules are not prerequisite to a planet.'

The method of chondrule creation suggested by the team revolves around something called 'jetting', which occurs at the beginning of an impact as the surfaces of two objects meet.

The rock caught in the pinch between the colliding objects is compressed to high pressure and intensely heated, creating a bright flash.

The heat is enough to melt rock and create droplets in the ejected debris that can become chondrules. 

An asteroid is a large chunk of rock left over from collisions in the early solar system. Most are located between Mars and Jupiter in the Main Belt. This illustration shows an asteroid breaking apart. Some asteroids are rich in metal, and it's thought others may have brought water to Earth

Meteorites that we find on Earth come from either asteroids or comets passing through the atmosphere and hitting the ground (illustration of an asteroid on approach shown). They were thought to be a snippet into the very young solar system, but may now be a snapshot of a later period