May 24, 2007
Our solar system came into existence with a nudge, rather than a bang, according to a meteorite analysis that rules out a popular theory for the formation of our planetary system.
Most astrophysicists believe that the solar system formed from a cloud of gas and dust when a nearby supernova exploded, compressing the dust and triggering the birth of the Sun and planets, says Martin Bizzarro of the University of Copenhagen in Denmark.
To investigate, Bizzarro and his colleagues looked for iron-60, an isotope produced by supernovae, in meteorites that formed during the first million years in the solar system's history. "To our great surprise, there was no iron-60, ruling out the supernova trigger mechanism," says Bizzarro.
The team found another isotope, aluminium-26, suggesting an alternative trigger. Aluminium-26 only forms in extremely massive stars, around 30 times the mass of the Sun, and such stars release a great amount of energy in winds loaded with aluminium-26, says Bizzarro. These winds could have buffeted the gas cloud, causing the solar system to form, he says.
There was also evidence of iron-60 in meteorites dating from a few million years later, suggesting that this massive star exploded at a later date, injecting iron-60 into the youthful solar system.
The team are now looking for evidence of other supernovae in our solar system's vicinity. "This could have been a very crowded and dynamic neighbourhood," says Bizzarro.