What Would Happen If The Sun Suddenly Exploded?

Of all the things to worry about, the explosion of our sun is perhaps one of the least pressing. The Earth has seen five massive extinction events, and it's therefore natural to wonder whether we, as human beings, will be the sixth. But if we are wiped out by some cataclysmic occurrence, it will almost certainly have nothing to do with the death of our sun, which at this stage is only about halfway through what is thought to be a 10 billion-year lifespan. That is to say, that in another 5 billion years, the sun will run out of hydrogen, marking the end of its life cycle, and the likelihood that we'll be around to witness such an event is infinitesimally small.

But let's say, for the sake of argument, that the human race is around for the collapse of our solar system's host star. Better yet, let's say the sun were to suddenly explode tomorrow. What would that look like from our perspective? Well, it goes without saying that none of it would be good. In fact, it would be immeasurably worse than any of the aforementioned extinction events our planet has thus far weathered. But just how destructive would such an event be? And is there any scenario in which the sun could spontaneously blow up?

There are seven main stages of a star's existence, and astronomers refer to stars that convert hydrogen into helium via nuclear fusion in their cores as "main sequence stars," which describes around 90% of all stars in the universe. The pressure produced by this process in a star's core pushes against the force of gravity, essentially ensuring the star itself doesn't collapse. But when the hydrogen runs out, that pressure is lost and gravity takes over. When this happens to a big enough star, it creates what's known as a supernova, wherein the collapse is so quick and contains so much force that it creates a shock wave which shoots the external parts of the star out into the surrounding space.

Thankfully, our sun isn't big enough to produce a supernova. It would take a star 10 times or more the size of the sun to create such an explosion. Instead, when the sun dies, it will do so in a much slower and arguably more terrifying way. The death of our sun will see it swell into a red giant — a dying star that is in the final stage of its evolution. During this stage, the sun's core will run out of hydrogen and begin fusing heavier elements. This will result in the internal temperature of the sun rising, causing a shell of hydrogen to start burning around it while the helium remaining in the core slowly contracts. As this happens, the temperature will continue to increase, transferring more energy to the hydrogen shell. It's this which will cause the sun to expand and become a red giant, swallowing several planets in our solar system, probably including Earth, in the process.

When our sun swells into a red giant, it will be catastrophic for our planet in more ways than one. As the sun expands it will consume many of the planets in our solar system, which will be instantly evaporated by the intense heat of the dying star. Astronomer Dimitri Veras at the University of Warwick told NASA, "I am confident that the Sun will swallow Mercury and Venus, and not Mars. But the fate of the Earth — which resides in between — is less clear." Either way, any life on Earth would likely be long gone anyway.

The expansion of the sun during its final phase would result in solar winds capable of stripping our planet of its magnetic field. This would remove our atmosphere and therefore our protection from dangerous solar particles and the sun's ultraviolet radiation. The final stages of the red giant phase would see the sun shooting material from its outer layers in what NASA termed "intense episodic bursts," and since the Earth would have been stripped of its atmosphere, it will essentially be bombarded with intense radiation from the dying sun without any protection, making the surface of the planet entirely inhospitable. Were we somehow able to witness this event from Earth's surface, however, the sun would have become so big and so bright that it would fill the entire sky.

What's more, the dying sun will likely throw off the orbits of planets that rely on the star's gravitational hold to remain on their current course. This will likely see orbits expand, with the outer planets drifting away and ending up double the distance from the sun as they were during its lifetime.

We know the sun will one day run out of hydrogen and become a red giant rather than exploding, but for the sake of argument, let's say the sun did explode. What would happen to our planet and solar system? 

Well, for one thing, if the sun did blow up, we likely wouldn't know about it at first. That's because light from the sun takes a while to reach us. Our host star is 93 million miles away, which means that sunlight takes 8 minutes and 20 seconds to arrive on Earth. So, even if our star blew up, the light emitted by such an event would only be able to travel at the speed of, well, light.

That said, we wouldn't be around to witness that light arriving on Earth, as all life on our planet would be immediately extinguished. So, while the explosion itself would not be visible when it happened, we would most certainly feel the effects of our host star exploding anyway.

As Chris Impey, University Distinguished Professor of Astronomy at the University of Arizona, points out, a supernova 30 light years away from Earth would be catastrophic as it would destroy or dramatically deplete our ozone layer, likely resulting in mass extinctions. But the sun isn't 30 light years away. It's 0.00001581 light years away. Were it to explode, we would be inescapably doomed, and we wouldn't even have time to think about it.

The neutrinos would be the thing to get us. These tiny subatomic particles are produced by atomic nuclei coming together — a process that constantly occurs in our sun — producing neutrinos that radiate omnidirectionally from their point of creation. Every day, we are hit with 10s of trillions of neutrinos from the sun but we're unable to feel them as they don't interact with our bodies. More specifically, the chance that a neutrino will ever interact with an atom in your body during your lifetime is one in four.

However, were the sun to explode, things would look a lot different in that regard. Every neutrino created in the supernova would have its flux increased by a factor of roughly 10 quadrillion. What's more, the energy contained in each neutrino would increase by a factor of 10, which would therefore increase the likelihood of the tiny particles interacting with the human body. As such, were the sun to explode and shoot out these supercharged neutrinos, within 1/20th of a second any life form on the surface of the Earth would be boiled from the inside due to the massive increase in neutrino interactions in their body. Since the particles are so small, we'd have no idea what was happening, either.

So, while it would take the light from an explosion 8 minutes and 20 seconds to hit Earth, by the time it did arrive, every living thing on the planet's surface would have been obliterated.

Along with all life on Earth, human beings would be almost instantly vaporized by the sun going supernova. But what would happen after we disappeared? Well, the Earth itself certainly wouldn't fare very well. Once radiation escapes from the imploded core of our sun, it would scorch all the planets in its path, including our own. The side of our planet facing the sun would have its atmosphere and oceans obliterated as the surface of the planet boils away. The opposite side would last slightly longer, but the energy from the sun's explosion would cause the Earth's temperature to reach roughly 15 times that of the sun's surface anyway, so nowhere on the planet would be safe.

Soon after, the blast wave from the sun's implosion would hit the Earth, likely destroying the planet altogether. Even if the planet did survive this wave of devastating radiation, it would likely only hold together for a couple of days at most, eventually disintegrating as a result of its scorched surface being eaten away, the massively increased temperature, and the blasts of the shock waves. Were the planet to somehow survive, not only would temperatures drop to unthinkably cold levels without a central star around which to orbit, Earth and all the other planets in our solar system would basically become rogue planets, drifting through space without anything anchoring them.