 If you're watching Space Twitter or the Space News today, there's a lot of people talking about a Chinese rocket, a Long March 5B rocket, piece of a rocket that's going to come back to Earth. And what makes this so sensational is nobody knows when or where it will land. What we know is that it's not controlled. There is no programmed deorbit burn that's going to put this thing into the ocean. Now, this sounds a lot like the Starlink secondary stage that came back over the Northwest, United States, about a month and a half ago, only this thing's a lot bigger. So all the buzz right now is about predicting where and when this is going to land and the troubling answer is nobody knows until a few hours before it happens because it's just a really uncertain problem. How much drag there is in the outer atmosphere and the tenuous, thin layers of the outer atmosphere is really hard to model. Now, Jonathan McDowell at Harvard CFA is like the go-to person, so I think he's fielded like 40 interviews in the last couple of days about this. Today on Twitter, there was a really obnoxious, in my opinion, comment about the likelihood of this rocket hitting anything. And it said it was like one in 200 million chance of it hitting anything. And I think this is totally misstating the probability of what's going to happen. The likelihood that this rocket is going to hit anyone in particular is super low. You should not worry about this rocket landing on you. The likelihood of this rocket hitting something, well, that's higher. I've been seeing a bunch of nonsense numbers floating around saying that it's a one in a trillion chance that it'll hit anything, that it's going to land in the ocean. So it occurs to me here on a Friday that we could find out a rough number. How do astronomers answer questions like this? How does an astronomer answer this question? What is the surface area that Earth we're dealing with? What's the total possible landing zone? According to the first result on Google is 5.1 times 10 to the 8 square kilometers. Everybody knows like 70% of it, two-thirds is water, something like that. So what's the area that we're actually interested in? What's the area? What we really want to know is what's the surface area of people? And I don't just mean like stacking all the people together. I mean like what's the area of the people and their houses and the cities and roads and you know like swing sets and maybe like farms. I don't know, I'm not an artist. What's the area of people? Because if we don't know anything about where it's going to land, if it truly is a random impact, then the probability I think we care about is roughly the surface area of people to the surface area of Earth. That's the number we care about. And so we need to figure out this unknown. More guesswork. Number of people. I don't know. What is it? 7.6. 7.6 billion people. So if we want to know how much area that people take up, it's going to be some area per person times the number of people. Order of magnitude guess. So how much area does each person need? I don't know. How much area do you use? It's more than a few feet. So how much? How much? How do we guess? Well, here we start looking for factors of 10. I mean, we share buildings and we share roads and farms and parks. It's more than 10 square feet, you know, that's just like the room you take up. 100 square feet. If I divide like the size of my house between all the people who live in it, it's closer to 100 square feet, I guess. But even that seems like an underestimate because I need some share of farmland and I need some share of roads and some share of everything else. A thousand square feet, a thousand square feet, that's like a 30 by 30 foot chunk. That seems small. But maybe. That's definitely the smallest. I definitely need at least a thousand square feet of land. Let's call that 100 square meters for round numbers. You need at least 100 square meters to live. That's probably way too small. 100 square meters times 7.6 billion. This is already going to be a big number divided by 5 times 10 to the 8th kilometer squared. So there you go. This is the odds that the rocket will land on something that we care about. It could be easily a factor of 10 higher, 0.15 percent chance. Okay, and like that is an approximate answer. Point one, maybe 0.2 percent. But I would easily believe that it's a factor of 10 higher, 1 percent chance of it hitting something. And this seems troublingly high if we're putting a ton of stuff in outer space. 1 percent that a chance that any given rocket is going to hit something we care about seems problematically high, especially when you can't control what that thing is going to hit. And this is why it's so important that rockets can control where the pieces come back down. And why when we see uncontrolled reentry events, like what happened with the Falcon 9 over Seattle a couple months ago, or what's going to happen to this Long March 5 rocket this weekend, it's really worrisome.