Missing Asteroid Mystery Mitigated

01 March 2009
Posted by Chris Smith.

There are asteroids missing from the belt between Mars and Jupiter, and now researchers think they were shoved out of place by two of our solar system's gas giants - Jupiter and Saturn, as they assumed their current orbit some 4 billion years ago.

JupiterWriting in the journal Nature, David Minton and Renu Malhotra from the University of Arizona identified gaps in the asteroid belt where there should be an even distribution of asteroids.  Many gaps, called Kirkwood gaps, exist because the gravitational influence of the planets make certain regions in the asteroid belt unstable.  These were originally identified by Daniel Kirkwood in 1857, but some of them have remained a mystery until now.

Minton and Malhotra designed a computer model of the asteroid belt, which took into account the gravitational influence that we already know about, but their model started with a uniform distribution of asteroids.  When they ran their model to simulate 4 billion years, they found that the Kirkwood gaps matched well to their observations, but that out in the real asteroid belt there were regions severely depleted in asteroids that normal gravitational influence could not account for.

There is already some evidence, the orbits of Pluto and Neptune for example, that the planets in our solar system have not always been in the orbits we find them in now.  Factoring this into account, and winding the clock back on the model, the observed gaps fit very well with the migration of Jupiter and Saturn to their present positions.  The researchers estimate that in the course of finding their place in the solar system, these gas giants may have caused the asteroid belt to have lost almost 95% of it's original pre-migration asteroids.

So the missing pieces of our asteroid belt can help us to fill in some of the missing pieces of the history of our solar system!

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