How do we know the ort cloud exists? Right, the ort cloud, this reservoir of comments, the source of long period comments, comments that have orbits longer than 200 years or so. How do we know it exists? Because we've never, ever observed directly the ort cloud. You know, we've seen asteroids in the asteroid belt. We've seen kooper belt objects in the kooper belt where we may have some indications of a region called the scatter disk, but that's another episode. But beyond that, beyond in that most distant edges of our solar system, we think there is a thing called the ort cloud, the ort cloud, the origin of most comments. But we've never actually picked up a telescope, looked deep into the sky, found a very distant object, said, yep, see that object right there? Or being about 40,000 astronomical units away. Yep, that is a member of the ort cloud. We don't. We don't. So how do we know it exists? Even though we can't see it, well, this is the game of science, right? Science is all about inference. It's about taking the available data, the available observations, what we do have, what we do have all the data and drawing conclusions from the data and developing hypotheses that can eventually be tested. And with the test, you make new observations or you come back through old data, looking for extra connections so you can validate or invalidate hypotheses. But it's at the end of the day, it's all inference. We have no direct images of objects in the ort cloud. But we do have data, we do have observations of messengers from the ort cloud. We have data, we have observations of when the ort cloud, which we're pretty sure it exists, sends a messenger into the inner solar system. One of its own members detaches from the ort cloud, plunges into the inner solar system. We can study that. We can study a comment. We can take pictures of a comment. We can trace the orbit of a comment and from the behavior of those members of those messengers, we can figure out the properties of their home, of their origin. And it was the middle of the 20th century when we first realized that these long period comments might have a common origin point because it didn't have to be true. Like every once in a while, there's a comment that appears in the sky. We can detect with telescopes, with observations. It's like, yeah, okay, brand new comment. We look in the historical records. We say, oh, this is a new one. This is a new comment that no one has ever seen before. And then it does its thing. It gets scattered out of the solar system or hits the sun or gets locked into a shorter orbit or whatever. And then we forget about it. And then a few years later, a few decades later, another comment, brand new comment appears. And for centuries, astronomers had been cataloging these new comments. And the question is, where are these comments coming from? Really? Just where are they coming from? What is their origin story for these comments? And in the middle of the 20th century, a few astronomers, especially Jan Orte, figured this out or made some very, very persuasive arguments because he started looking at the statistics of these new comments, these brand new comments that had never been seen before. And asking some real questions about the observations. One thing he noticed was that these new comments come from all directions in the sky. Times they're along the plane of the solar system, but a lot of times they come from up or down, you know, sideways, it doesn't matter. It didn't matter. They're coming from all over. Okay, that's interesting. And he also noticed or argued that comments don't live long. Comments don't live long because they either eventually crash into the sun or they encounter a giant planet and get kicked out of the solar system or they exhaust themselves as all their ices melt and evaporate and turn into cometales after a few passes, like a few dozen or a few hundred passes, there's not going to be any ice left. You know, just be inert. It will be dead. You won't be able to see it anymore. So comments come from any direction in the sky. And it's not the same comments every time. There are, it has to be new comments. There must be a reservoir of comments. There has to be a storage facility of comments that send new comments into the solar system every once in a while. And this was the first step. And then the big, big, big realization was by examining the orbits of these new comments. You can see, you know, they come in, they're tracing orbits as they get close to the sun and then they circle around. And once you get enough data, you can reconstruct the entire orbit. You can rebuild that entire orbit. You can see, okay, this is the entire path. Like we're just catching one little leg here like the final turn before the finish line. But with that data and we know math and gravity and everything, you can construct the whole thing. And when you construct the whole thing, these new comments are very elliptical orbits. And they have an Appelian. This is the farthest distance from the sun. They had a relatively common Appelian. So no matter where these comments were coming from, they started on average about 20,000 AU away, astronomical units away. That's 20,000 times further from the sun than the Earth is. So whatever's causing long period comments must be a reservoir. It must have a lot more comments than we're seeing. And only occasionally send in new ones because comments don't last long once they encounter the inner solar system. So every time it's a new comment, it really is a new comment. This reservoir must be evenly distributed all around the solar system. And it must be at around 20,000 AU. It's a way, you know, plus or minus. It's a cloud of comments in the outermost regions of the solar system, the org cloud. Thank you so much for watching. I hope you enjoyed. Don't forget to like and subscribe and go to patreon.com slash pmsr to help me. Make this stuff happen. And I will see you next time.