字幕表 動画を再生する 英語字幕をプリント With the vastness of the Universe, everything in it seems so spread out. But some objects are closer than you might realize. Every now and then, a random interstellar asteroid passes through the Oort cloud, the wall of icy debris at the very edge of our Solar System. But what if a rogue star unceremoniously rampaged right through the Oort cloud? How bad would it be, if it brought other planets along for the ride? What if I told you that a rogue star has already invaded our Sun's territory? A dim red dwarf, dubbed Scholz's star, crossed the Oort cloud some 70,000 years ago. It passed just 0.8 light-years away from the Sun. And then it made a turn in the opposite direction, without causing much trouble. Right now, another rogue star is moving in our direction. Gliese 710 has about 60% of the mass of our Sun, and it's traveling across the galaxy at 52,000 km/h (32,000 mph). If another star rampaged through the Solar System, the extent of the chaos it would cause would depend on the size of that star, and its trajectory. When Scholz's star passed through the Oort cloud, it came five times closer than Proxima Centauri, the closest star to our Solar System. Scholz's star didn't have much effect on Earth, although around the same time, early humans almost got wiped out by a massive volcanic eruption. But that was pure coincidence, right? In any case, before Scholz's star turned away minding its own business, it did change the orbits of about 10% of comets and asteroids in the Solar System. But, what if it was a bigger incoming star, like Gliese 710, that's currently making its way towards us? Gliese 710 isn't scheduled to make its first contact with the Solar System for another 1.29 million years. But when it does, it could shake the Earth quite a bit. At first, the rogue star would make its way into the Oort cloud. At this point, it wouldn't affect us directly. But it would send massive chunks of space rock showering the Solar System. About 170 meteors, comets and asteroids would hit the Earth every day. That's ten times more than what's bombarding our planet right now. Comets and meteors might not seem like a big deal, since most of them are small, and they often fall in unpopulated regions. But... Back in 1908, in Siberia, it only took one asteroid to obliterate 80,000 trees, and blow out windows 60 km (37 mi) away. If the same asteroid were to hit New York, the entire city would be in the impact zone. And that's if just a single star smaller than the Sun slightly made it just inside our Solar System. If a star larger than our Sun entered the Oort cloud, it would disrupt the orbital cycle for every planet it passed. Since there are such large distances within the Solar System, this disruption would happen over the span of millions of years. It would be an almost slow-motion chaos of debris waves. It might even set some planets on a collision course. And that's not the worst it could get. If the rogue star had other planets and moons following it, our Solar System would turn into a galactic soup, with stars and planets being pulled out of their orbits. Massive collisions would create a rippling effect, disrupting planetary orbits even more. Eventually, the Earth would be knocked out of its orbit too, if it wasn't already destroyed by meteor storms and the remnants of other planets. Not to sound too dramatic, but there are estimates that 40,000 stars have entered the Oort cloud, at some point in the history of the Solar System. But... They all came here on "just visiting" trips. Chances that any of those rogue stars will ever make it past the Oort cloud are close to zero. Let's just hope that we'll never have to deal with anything like a black hole coming too close to the Solar System. But that's a story for another WHAT IF.