字幕表 動画を再生する 英語字幕をプリント In October of 2017, our solar system had a very strange visitor. We now call this oblong mass 'Oumuamua, which simply translated means 'scout' in Hawaiian. When it passed by our Sun, it brought more questions than answers. What is it? Where did it come from? Why is it here now? A brand new study may finally bring answers to all these questions. Initially, many thought the unusually elongated interstellar object, or ISO, was a comet. But it was missing several key characteristics of a comet, like the coma and the tail. So, of course, it's gotta be aliens, right? One key piece of the puzzle that made 'alien spaceship' jump to mind was just how freakin' fast it was going. It zipped past the Sun at about 87.3 kilometers per second—that's way over the legal speed limit. I mean, way faster than it would be going if it were solely influenced by the Sun's gravity. The team that published this proposed hypothesis for 'Oumuamua's origin story may be able to explain everything about it that has mystified us for the past three years. The idea goes like this: once upon time, some body in another solar system got a little too cozy with its system's star and BAM, it was ripped to shreds by the tidal forces from that star, a process called tidal fragmentation. The scientists tested this idea out in simulations that modeled what would go down if three kinds of bodies got too close to their host star. One: kilometer-sized comets from the Oort cloud, the very farthest region of our solar system; two: kilometer-sized planetesimals, which are like little baby pre-planets; and three: full on planet-sized bodies called super-Earths, even farther away from their star than we are from our Sun. The results of these simulations were clear: if any of these items came within roughly 350,000 kilometers of their star, the tidal forces exerted by that star would tear them to shreds. Tidal forces in space are the result of gravity pulling on stuff. Just like the moon's gravity pulls on the Earth's oceans and causes our tides, stars pull on all of the things around them, too. Like, did you know that our Sun also affects our ocean tides? Not as much as the moon does because of how much closer the moon is to us, but still. So, between any two objects, both are exerting gravitational pull on each other and the gravitational force increases with mass. So smaller bodies, like the comet-like objects, have to get closer to their host star to be ripped up. But for big objects, it's much easier to get torn up at a distance by that tidal fragmentation, all just because of the way gravity works. This proposed explanation takes care of the strangest and most inexplicable parts of the interstellar mystery we've had on our hands. Based on these simulations, 'Oumuamua's distinctive elongated shape matches how objects would look if they broke apart due to tidal fragmentation. And the speed at which it passed us by could be explained by that fragment being forcibly ejected by its host star after being shredded. The team behind this study hopes they'll get to observe more ISOs like 'Oumuamua so they can gather more data and shore up their models. And studying bodies like 'Oumuamua will tell us more about their composition, and could even indicate if they could possibly host any life. And that's important because one of the main scientific hypotheses for how life began on Earth is that it may have been brought to our planet by an interstellar object. So studying one flying by could give us more insight into our own origins! So unfortunately, it's probably not an alien spaceship. At least, not this time. I'm not giving up hope. And a piece of a planet that was banished by its star is pretty cool too— and at least we got to wave as it went by. Keep coming back to Seeker for all your earth shattering astrophysics news, and if you have another astronomical headline you want us to cover—not astrological, we don't do those— then leave us a comment down below. I'll see ya next time and as always, thanks for watching.