Asteroids may have flocked together to build planets

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London, August 18 (ANI): New computer simulations have suggested that dense swarms of asteroids collapsed under their own gravity to make the building blocks of the planets in our solar system.

The planets are thought to have formed from a disc of dust and gas around the infant sun.

The initial process is well known: dust grains clumped together, forming objects in the millimetre-to-metre range.

However, it is not known how the growth process continued.

The gas in the disc should have put a drag on the new boulders, causing them to spiral into the sun before they could grow further.

According to a report in New Scientist, evidence is now mounting that the next step was a sudden leap forward, skipping intermediate sizes to make asteroids hundreds of kilometers across - massive enough to resist gas drag.

Asteroids hundreds of kilometers across appeared - too massive to be dragged into the sun

This basic idea is decades old, but it attracted renewed attention in 2007 and 2008 following simulations by a team led by Anders Johansen of the Max Planck Institute for Astronomy in Heidelberg, Germany, and by another team led by Jeffrey Cuzzi of NASA's Ames Research Center in Moffett Field, California.

These showed that turbulence in the nebula could have concentrated objects less than a meter across in dense enough swarms to collapse under their mutual gravity and form large asteroids tens to hundreds of kilometers across.

"If either one of these models turns out to be right, this will be a big step forward," said John Chambers of the Carnegie Institution in Washington DC.

Now, a new study has found evidence that such a process did occur in our solar system. It is based on the size of objects in the asteroid belt.

Estimates from telescopic surveys suggest there are millions of the smallest asteroids, which are less than a kilometer across, with the numbers of larger ones dropping off sharply.

Yet this size distribution and number would once have been different: asteroids can grow by sweeping up smaller objects, and shatter if they collide with an object of similar size.

Alessandro Morbidelli of the Cote D'Azur Observatory in Nice, France, led a team that simulated the evolution of the asteroid belt, modelling a variety of starting populations.

They did find a good fit when they started with a mixture of sizes between 100 and 1000 kilometers across, suggesting that large asteroids did form spontaneously during the solar system's development. (ANI)

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