Something peculiar in my 2yo's bedroom led me to a revelation about our universe
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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.
https://en.m.wikipedia.org/wiki/Stability_of_the_Solar_Syste...
I'm trying to figure out what this is supposed to mean. Of course we don't know exactly, but also of course we have some idea.
Like, could Venus have had an eccentric orbit that extended further from the Sun than Earth or closer than Mercury? Could it have had a moon?
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.
Figure 4 in this paper shows the object's trajectory in the frame of Venus:
https://en.m.wikipedia.org/wiki/Provisional_designation_in_a...
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.
I'm starting to get the hang of nitter.net and here's the thread.
https://nitter.lanterne-rouge.info/latifnasser/status/175095...
Other nitter instances were rate-limited or down. This one worked for me.
It's actually interesting.
I think it's time for the good samaritans of HN to post nitter links for every X (formerly Twitter) post.
Also, is there some extension which I could add in the browser which would show the corresponding Nitter link?
But as the other commenter said Libredirect is the way to go: https://libredirect.github.io/
Too bad we have to devise technology to solve problems that technology in the wrong hands has created. I've been taking notes for years.
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).
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.
* I originally said Reply-All