字幕表 動画を再生する 英語字幕をプリント Jupiter. Uranus. Saturn. Earth? Sadly, the Earth didn't make it onto the list of the Solar System's ringed planets. This is WHAT IF, and here's what would happen if the Earth had rings like Saturn. When the Earth was young, it most likely had a ring of rock debris around it. 4.5 billion years ago another planet, Theia, hit the Earth. The giant impact sent a ring of matter hurtling into the Earth's orbit. But it didn't stay like that for long. The rocky debris soon formed another celestial body - the one we now call the Moon. Having planetary rings visible in the sky would look way more spectacular than just one grey rock, right? Maybe. But if our planet got beautiful rings like these tomorrow, much of life on Earth might not survive the renovation process. It wouldn't necessarily take another collision to form rings around the Earth. We could just crumble the Moon. And for that, we'd only need to move it a little closer. The gravitational pull that our planet exerts on the Moon isn't equal everywhere. It's much stronger on the side of the Moon that is closest to us. There is a limit on how close celestial bodies can be to each other. It's called the Roche limit. If they get any closer than that limit, the larger body shreds the smaller one into pieces. The distance of the Roche Limit depends on the size, mass and density of the two objects. For instance, the Sun rips up comets that comets within 1.3 million km (0.8 million mi) of it. The Earth will tear apart an average-sized comet from approximately 18,000 km (11,185 mi) away. For the Moon, the Roche limit would be 9,500 km (5,900 mi). The rings we might get from something the size of the Moon would be about 5,000 km (3,100 mi) wide and around 9.5 m (31 ft) thick. But unlike Saturn's icy rings, ours would be made of nothing but rock. The Earth is just too close to the Sun to keep the debris iced. Looking out at the sky, you'd be able to see these rings from Earth at all times. Because of the brightness of the rings, the Moon wouldn't seem as bright anymore. That is if we still had the Moon. If the Moon crumbled up and became our rings, there'd be nothing else up there to look at. And there would be some other consequences. The rings suddenly hugging Earth would disrupt internal navigation systems of some animals. If not enough direct sunlight was making it through the rings, they would also affect photosynthesis and our oxygen supply. In the shadow of the rings, with no contact from the Sun's rays, the temperature would get so cold that it would make the shadowed areas of the Earth almost uninhabitable. Communications satellites, generally placed around the Earth's equator, would find themselves right in the middle of a rock storm. We'd need to find another way to keep the internet alive if we want to keep posting selfies on a ringed Earth. We'd be better off in a scenario where the Earth has always been like this. Provided we didn't lose sunlight and oxygen, we'd evolve just fine. But we'd have to develop other means of communication since we wouldn't be able to send satellites into an orbit full of rocks. Space would never become our final frontier. The rocky rings around the planet would be a sort of orbital barbed wire fence keeping us all grounded. And, just like the rings of Saturn, Earth's rings wouldn't last forever. One day they'd start to feel their age and drop from the sky. Make sure to wear a helmet, and don't forget to look up and enjoy the show. If the multiverse is real, there might be a ringed Earth somewhere out there, with people on it wondering what it would be like to live on a planet with no rings. But we'll leave that story for another WHAT IF.