Somtimes it's hard to appreciate a good thing till it's gone. But would the end of sunlight really mean the end us?
First, let’s be clear on one point. The Sun can’t be “put out” like fire on Earth, and it’s unlikely that such a massive ball of burning gas could suddenly dissipate. Still it’s an interesting thought experiment — what would happen if it vanished?
The Sun produces the same amount of energy per second as 100 million hydrogen bombs, and it’s responsible for life on Earth. It’s also the gravitational lynchpin of the solar system, without which none of the planets would have even formed. So if the Sun were to implode or otherwise wink out of existence like a dead lightbulb, what would actually happen here on Earth?
Because of our distance from the Sun, we wouldn’t even know that the sun had disappeared for approximately 8 and a half minutes. We would still see its ghost floating in the sky until its last rays of light reached us through space. At that point, eternal night would fall, pierced only by starlight — even the moon would fade away, since it doesn’t produce any light of its own.
As those last sunbeams die away, so will the main processes driving life on Earth. Without sunlight, plants can no longer convert energy into food through photosynthesis. They wouldn’t die immediately, and some trees could probably last a few decades given their slow metabolism and considerable storage space. But as the eternal night stretched on and on, the entire base of the food chain would eventually die off followed by herbivores, carnivores, and the rest.
But even before we ran out of food, the Earth’s surface would cool beneath livable temperatures. Within the first week, average global surface temperatures would drop below -20 degrees Celsius, and by the end of the year down to -100 degrees Celsius. The oceans would completely freeze over except surface layer of ice which would actually insulate the waters beneath. Shielded from the colder air, the waters could remain liquid for hundreds of thousands of years.
While life on the rest of the planet would soon extinguish, those oceans could still harbor life. Life on Earth has certainly enjoyed a boost from the Sun’s energy, but our planet has its own store of heat leftover from its formation. This heat radiates from the core out of hydrothermal vents on the ocean floor, where complex ecosystems have thrived for billions of years. Even without a local star, these lifeforms would happily survive on geothermal energy for billions of years more.
In fact, this is exactly the kind of life system that astronomers believe could exist on icy moons in the outer solar system. Enceladus, for example, also has hydrothermal vents beneath its frozen crust that have exhibited traces of organic compounds. If the Sun were to vanish, a new icy Earth would become startlingly similar to these other worlds: vast stretches of bleak ice with pockets of rich life surrounding the volcanic hot-spots dotting the oceanic abyss.
Of course, we can’t forget the Sun’s other major effect on Earth: gravity. According to general relativity, the cessation of the Sun’s gravitational pull would also take a while to reach us. Einstein proved that the force of gravity actually travels at the same rate as light, so our planet would continue orbiting the Sun’s empty space like a forlorn groupie. But after those 8.5 minutes, Earth would be released from the Sun’s gravitational tether, and we would fly off at exactly the same speed we always move: about 30 km per second.
So would all the other planets and celestial bodies in the solar system, which means our chances of surviving the melee of space junk hurling outwards are pretty low. Provided we did manage to escape the solar system unscathed and stay out of the way of any neighboring stars, Earth could continue soaring undeterred through the vacuum of space at the same velocity. Or it could get tugged into the orbit of another star, or even swallowed up by a black hole. Either way, we won’t be there to see it.