Comment by ddahlen
2 days ago
I'm one of those astronomers! I'm working on my PhD in orbital dynamics.
A lot of people are requesting discretionary time on telescopes trying to get observations in. The orbit will put us on the other side of the sun when 3I is nearest the sun in october, we can see it now and after it comes back out from behind the sun.
Unfortunately, right now the it is in a very crowded star field (IE, its close to the galactic plane, lots of stars in the background).
If you are interested in orbital dynamics, I have an open source rust/python package for accurate orbital calculations of asteroids/comets:
Cool to see! I spent a few years working on asteroid orbital dynamics too. What integrator are you using? Do you cover the weird stuff like Yarkovsky effects? That gets important for NEO impact risk, which is what I worked on.
Matt Holman's ASSIST (https://github.com/matthewholman/assist) struck me as a breath of fresh air, coming from openorb and its kin.
I wrote a custom implementation of the Radau integrator, its been heavily modified. I have a lot of additional physics, it supports the non-gravitational models that JPL Horizons defaults to, so diurnal yarkovsky at least. I've been using it to study dust and small object dynamics, as they get pushed around by the sun a lot.
It does an OK job for impactors, but the integrator is tuned heavily for performance, and the tolerance defaults are not great for impactors.
I match jpl horizons for apophis to a few km, they have a lot more intense earth gravitational model then I care to implement, and by default I only include the 5 heaviest main belt asteroids, they have many more. That was the sweet spot for accuracy vs speed for me, overall accuracy goal is less than a few km over a decade.
The goal is to be able to handle the huge influx of new asteroids that the catalog will have due to LSST and eventually NEO Surveyor (which I worked on for 3 years). Most systems I know have been throwing hardware at the problem, I tried to make fast and efficient enough software that we can use it on a laptop for 5-10 million asteroids.
You might want to try OrdinaryDiffEq.jl. As of last summer, we have really fancy radau methods that are arbitrary order, arbitrary tolerance (see https://arxiv.org/abs/2412.14362 for the paper)
That is very impressive - getting the nongravs is a lot of work.
Anything published on your integrator and its modifications?
One nice feature of ASSIST (from what I remember, its been a while) was that I could add in more perturbers and crank up the gravitational harmonics if I wanted to. It sounds like you support that too at least for perturbers?
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How does Kete differ from REBOUND? (https://rebound.readthedocs.io/en/latest/)
Different goals, kete is meant to be aimed more toward observers and telescope data processing, all asteroids and comets at once on a laptop. Short term analysis (<100 years) and speed are the priority.
Is there a rule of thumb speed where an object is considered not from this solar system?
Eccentricity!
You can approximate the orbits of basically everything in the solar system using 2-body mechanics (IE, ignore the planets). If you do this you get orbits which are elliptical (eccentricity <1), parabolic (eccentricity = 1), or hyperbolic (eccentricity>1).
If the object has an eccentricity above 1, its not bound to the solar system.
Many long period comets have eccentricity hovering near 1, often these long period comets will be on their first pass (sometimes only pass) through the solar system. These comets though usually dont get much above eccentricity of 1. The 3 interstellars we have spotted have had like 1.2 or bigger. This one is above eccentricity 6! Its moving fast.
Edit: I have heard that when the first interstellar was found it actually broke a lot of peoples code, as it was common to hard code limits to allowed eccentricities (or simply not support ecc>1 at all).
This thing actually crashed our observatory software because we were trying to calculate position at too far of time horizons where because of the eccentricity the algorithms would not converge… that sucked but has been fixed. Ready for the next one!
> often these long period comets will be on their first pass (sometimes only pass) through the solar system.
Only pass because of the eccentricity, or for some other reason?
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https://en.wikipedia.org/wiki/Escape_velocity#Calculation
(assuming it hasn't interacted significantly with any other object in the solar system besides the sun)
you lucky so and so
many things are labeled historic, though some very very tiny number will actualy retain the power to inspire as this event will we have all dreamed of going into space to discover whatever is there, but as it turns out these interstelar objects are bringing us the only real physical evidence that we will ever get a good look at