When the Sun Formed, a Supernova Exploded Nearby. How Did the Solar System Survive It?
One of the scariest things that can happen to a planet is when a supernova explodes not far from it. We have evidence that various supernovae happened near the Earth in the past… and one of them came just as our planet was born. How did our young Sun survive it and what effects did it have on our planet?
The Crab Nebula, the remnant of the supernova astronomers observed in 1054; Source: Wikipedia
Around 1400 light years away sits one of the most prominent nebulae of the nightsky: the Orion Nebula. Even in light-polluted skies, the constellation Orion is hard to miss. The nebula as part of Orion’s Sword is a popular subject for amateur astronomers and astrophotographers. It’s so famous that the first photograph of it was already taken in 1880!
However, the Orion Nebula is just part of something much bigger — the Orion molecular cloud complex, aka the Orion complex. It’s one of the most active regions of star formation in our galactic neighborhood, with many young stars residing here, still in the making.
Multiple young stars with protoplanetary disks (from which planets form) have been photographed by space telescopes. The Hubble Space Telescope documented about 150 of them!
Stellar nurseries such as those in the Orion complex are beautiful to look at, as there’s always something to see; after all, these are busy spaces.
The Sun was also once part of such a stellar nursery when it was born 4.6 billion years ago. It had a swirling protoplanetary disk from which everything that surrounds us today formed. (I wonder if someone also took a photo of our young Sun…)
In comparison to our quiet stellar neighborhood these days, the young Sun lived in a buzzing place with stars much closer than they are today. The Sun was also surrounded by a lot of bigger stars — that had some consequences for our young system. But not all of them are negative.
Generally, bigger stars = shorter life spans. For such stars, the end fate is different from our Sun’s. While our Sun will one day grow to a red giant and then gently shed its layers into outer space, big stars end in massive supernova explosions.
These explosions temporarily shine brighter than the entire galaxy, making for a stunning sight. In the immediate neighborhood of a star gone supernova, mayhem reigns. Any habitable planet too close will essentially be rendered uninhabitable.
When scientists looked at the isotope ratios of meteorites they made a shocking discovery: a supernova must have exploded not far from our Sun when it was still in its beginning stages.
Meteorites are good test subjects as they haven’t changed at all in the 4.6 billion years the Solar System existed. Try to find evidence of that early time on Earth, with its plate tectonics and environmental activity, and you’ll have a hard time; but meteorites are fossils full of information.
And in these meteorites, scientists found a significant abundance of nickel-60 — this could only have been produced by a nearby supernova at this time.
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| The Sun seen in ultraviolet light; the Sun was born in an open cluster amidst other stars 4.6 billion years ago. Its properties make it more of a unique star, being larger than most stars in the galaxy. Source: Wikipedia |
In other words, a ticking time bomb resided just one light year from the developing Sun. In comparison, the closest star today is Proxima Centauri, 4.3 light years away.
On celestial scales, one light year is nothing. And the so-called “kill zone” for a supernova (that would render Earth uninhabitable) extends up to 50 light years away! If a supernova occurred one light year away today, we can get ready for doomsday.
Luckily, this won’t happen — and luckily, the Sun survived the powerful blast 4.6 billion years ago. But how?
Now, a star in development is no weakling. Stars form inside molecular clouds and within these, filaments exist which protect young systems in the making. It was such a filament that saved the Sun from the toxic radiation of the supernova. Some of the elements released in the explosion seeded our Solar System anyway, which is why we can still trace them to this day.
This also means that Earth received a fair share of heavier elements, potentially even driving the formation of life on our planet.
So, a happy end!
A supernova this close today would be our death sentence. But back then, the Sun survived one of the most powerful explosions in the entire universe—we truly are part of something unique. It must have been a blinding sight, that supernova just a light year away.
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