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Migrating planets caused meteor storm

Meteor storm Migration of giant gas planets such as Jupiter created the biggest meteor storm in our solar system's history, according to a new study.

The research in the journal Nature Geoscience paints the clearest picture yet of the causes of the Late Heavy Bombardment, a cosmic tempest 3.9 billion years ago, which shaped the solar system we have today.

Scientists have long hypothesised the bombardment was caused by planetary migration, as Jupiter and Saturn moved closer in towards the Sun, while Neptune and Uranus moved further out from where they formed.

The gravitational effects caused by these migrations flung large numbers of meteors towards the inner solar system, where they collided with the terrestrial planets, including the Earth and Moon.

They are also credited with sending the asteroids and comets into the orbits they have today.

The new paper by researchers including lead author Dr Simone Marchi from the Southwest Research Institute, in Boulder Colorado, supports this hypothesis based on a new study of Apollo 16 Moon rocks, and two major types of meteoroids.

These include high-metal H-chondrites which make up almost half of all meteors and meteorites believed to have originated on the main belt asteroid Vesta.

Marchi and colleagues used argon isotope readings to determine when the impacts that created the samples occurred.

Their models and computer simulations indicate a period of intense meteor bombardment thoughout the inner solar system between 3.4 and 4.1 billion years ago, coinciding with the Late Heavy Bombardment.

The argon readings also indicate that the meteor samples could only have resulted from high velocity impacts in excess of 10 kilometres per second.

Migration debate

Support for the Late Heavy Bombardment theory had waned after revelations that some lunar zircons and breccias caused by impacts are older than four billion years, and some 3.9-billion-year crater impact dates were all derived from a single large impact site known as the Imbrium Basin.

These findings raised the prospect of an alternative idea that the dates represent impacts from a smoothly declining bombardment of leftover planetary construction material.

But planetary scientist Dr Simon O'Toole from the Australian Astronomical Observatory says the new paper addresses doubts about planetary migration in our solar system.

"The new argon calculations provide an important result filling holes in existing planetary migration models for the Late Heavy Bombardment theory," says O'Toole.

"Previous models predict only low velocity impacts under five kilometres per second occurring in the asteroid belt," says O'Toole.

"Higher velocities would have placed these asteroids on planet crossing orbits, crashing into planets and quickly emptying out the asteroid belt."

However the gravitational influence of the migrating planets changed the orbits of the asteroids sending them far above and below the orbital plane of solar system reducing the risks of a planetary collision, says O'Toole.

"[The study] provides us with a good foundation stone for a better understanding of the early solar system and how it got to look the way it does now."