Read more: Cosmic accidents: 10 lucky breaks for humanity
Hydrogen, helium, interstellar dust – the ingredients of a solar system. Just stir together and set on fire
Matter prevailed, and it didn’t look back. As the universe cooled, stable atoms and molecules soon formed. One hundred million years on, the first stars, giants of hydrogen and helium, appeared. They lived fast and died young in huge explosions that seeded the cosmos with heavier elements, the ingredients of later stars and galaxies. Among those galaxies was the Milky Way. Little of note happened in one of its corners until some 9 billion years after the big bang.
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What does it take to make a solar system? Hydrogen, helium and a sprinkling of the dust that fills the space between stars. All these were hanging around our corner of the cosmos in abundance well before 4.6 billion years ago. But more was needed: a spark to set that inert gas cloud on fire.
Clues to the nature of that spark lie preserved in meteorites. Unlike the often-melted and mixed-up rocks native to our planet, meteorites have remained virtually unchanged since they condensed while the solar system was forming, preserving the chemistry of those early millennia.
One particular meteorite discovered in 2003 in Bishunpur, India, contained large quantities of iron-60, a radioactive isotope that decays over a few million years into stable nickel-60 (). Because iron-60 is so short-lived, interstellar gas generally holds just a trace of it. The large amounts in the Bishunpur meteorite imply that our solar system formed from a much richer brew.
The likelihood is that this brew was spiced up by a nearby supernova. These massive stellar explosions are one of the few cosmic processes known to create large quantities of heavy radioactive isotopes such as iron-60. Shock waves from such a supernova could have triggered the formation of the sun and planets by compressing the primordial gas cloud.
Or the conception of the solar system might have been a gentler affair. According to new calculations, a red giant star of sufficient size could rival a supernova in iron-60 production and produce other radioactive elements . These elements would be forged in a deep layer of the star, carried to the surface by convection, and ejected as part of a powerful stellar wind that could also stir up any gas clouds nearby.
Whether it was explosion or ejection, the sun is only the most obvious star we have to thank for our existence.
