> Anyway, I think this is so cool because everything else on the solar system map is so regular and orderly, but not quasi-moons!
Nothing in the solar system is regular and orderly. It's chaotic because 3-body problems are almost always chaotic, and >3-body problems are always chaotic.
Our solar system is a hundred-body problem (or more depending how small a "body" you want to include).
So why then does our solar system mostly appear to be regular and orderly? Because of the time scales we care about, and because for the majority of bodies (not Zoozve!), only one other body produces the overwhelming majority of gravitational influence. Which means we can cheat and treat many very short-term predictions as 2-body problems.
Over a one-month timeframe we can predict the solar system analytically as a bunch of 2-body problems. Easy.
Over a few hundred years we can use numerical methods. Harder, but it mostly works well enough.
Over a million-year timeframe it's completely hopeless. We have no idea where Venus will be exactly a million years from today.
Edit: 10 million years is a better threshold for hopelessness. A million years is still somewhat predictable for some bodies.
We must have some idea where the planets were back in the time of dinosaurs. I mean, Earth was still approximately the same distance from the Sun, and presumably still #3 right?
Probably the order of the planets was the same but we can't be sure of the eccentricity of their orbits back then. We do know Saturn probably didn't have rings back then.
Sorry I should have been more specific. We can't predict the accurate position of Venus in its orbit ten million years from now, and it's possible its orbit will have a different shape then too. However it's unlikely that the orbit would be so eccentric that it would intersect with Earth's orbit. That kind of deviation becomes more likely when we talk about a billion years.
What's the definition of chaos here? I thought chaos implied the measurement error growing quickly during propagation, but here it looks like it's growing pretty slowly. In what way is this more chaotic than the movement of a single accelerating body (where the error grows linearly with time)?
Chaos requires nonlinearity. A gravitational body's motion affects every other body, which in turn affects the original body, etc. So you can't analyze the parts of the system independently and then just add up the results. A body's motion indirectly affects its own future motion. Spacetime tells matter how to move and matter tells spacetime how to bend, as Wheeler said.
In two-body problems, this infinite recursion converges to a closed-form solution, which means we can just write down the solution to the differential equations that describe the system's state and predict it at any time in the future.
Unfortunately there are no true two-body orbits in the universe.
And with 3 and greater numbers of bodies that pleasant closed-form convergence doesn't happen. You get sensitive dependence to initial conditions (SDIC), with faster-than-linear divergence, and you can't solve the differential equations: You have to integrate them numerically.
The time horizon over which this divergence happens for planets is long relative to the time horizons we care about, but it's still SDIC and it's faster than linear. The same thing happens with the weather (the "butterfly effect") but there the time horizon for divergence (the Lyapunov time) is short enough that we humans can easily notice it.
> Zoozve orbits one thing: the sun. It spends all day every day doing that. BUT Venus also has a teeny gravitational toehold on it such that it ALSO ORBITS VENUS AT THE SAME TIME.
> It’s a whole new category of thing. Something that orbits a star and a planet at once. Something that is not a moon, but also not not a moon.
> They call it … a quasi-moon.
> Astronomers had been speculating that such an object could exist for 100+ years, but this was the first time anyone saw one … not only in our solar system but in the entire universe!!
He then goes one to describe how weird the paths of quasi-moons can be.
Where I think he's off is that it was not that Zoozve was orbiting both the Sun and Venus that was new. Astronomers have for hundreds of years known of a case of something orbiting both the Sun and a planet (see below).
What was new was the weirdness of the orbit.
The long known example of something orbiting both the Sun and a planet is the Moon. The Wikipedia article on the orbit of the moon [1] has a plot showing a section of the Earth's and Moon's trajectories around the Sun and you can see from it that they both trace a convex shape. That's because the Sun's pull on the Moon is about twice as strong as the Earth's.
From the Sun's point of view both Earth and Moon are in separate orbits that have been distorted so that they are rounded dodecahedrons. They are like two cyclists racing on a circular track, taking turns passing each other on the inside but at all times both are turning left.
Compare to other (non-quasi) moons. Most (all?) of them are more attracted gravitationally to their planet than to the Sun. The plots would not be convex. From the Sun's point of view plots of their paths would look like something from a spirograph.
If alien astronomers knew of the Earth and Moon but did not know their sizes, so all they had was their masses and orbits, they would probably actually classify them as a double planet rather than a planet and a moon.
What disqualifies the Moon from being a planet under the current Earth astronomy definition is that the center of mass of the Earth/Moon system is below the surface of the Earth.
The thread is about an object in our solar system, called 2002 VE. Its motion under the influence of gravity isn't clearly "an orbit", but (for now) it sort of follows closed loops when viewed from the moving frame of Venus, so people call it a quasi-moon of Venus.
Figure 4 in this paper shows the object's trajectory in the frame of Venus:
> we don’t live in a big clockwork, we live in a dance club
These chaotic orbits remind me of the chaotic solar system in Liu Cixin's novel "The Three-Body Problem". And they give me the same sense of terror that we can't predict where these objects will go.
Only on time scales like thousands of years or more, that are too long to worry about as far as any danger to Earth is concerned. On shorter time scales we can predict orbits very accurately, which is how astronomers know about objects that will pass near Earth decades in advance.
Most of the time you can just replace twitter.com with nitter.net or nitter.it but when these instances are down or blocked you can use other instances listed here: https://github.com/zedeus/nitter/wiki/Instances
Libredirect is the tool I typically use to get redirected to one of these sorts of mirror sites. That said, it won't pick a working Nitter instance, you might need to look up a list and find a few that work well.
I spent way too long trying to find a way to read this without making an account on X, so here's the recap:
An illustrator accidentally mislabelled a quasi-satellite named 2002-VE68 as a moon of Venus called “ZOOZVE" on a children's map (Venus doesn't have any proper moons).
Yes, the story is essentially linked to a podcast called Radiolab* that has used the story as a story pitch about submitting the name for the the asteroid.
The link isn't the thing-itself, it's part of a media campaign. The naming committee apparently has two dangling votes left for the decision. The podcast came out today and the decision is expected in the next few weeks.
Are you sure it was Reply-All? Their latest show listed is Sept 2023 on https://gimletmedia.com/shows/reply-all and nothing newer shows up in my podcast app.
https://nitter.lanterne-rouge.info/latifnasser/status/175095...