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125 points bikenaga | 2 comments | | HN request time: 0.508s | source
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ddahlen ◴[] No.44535954[source]
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:

https://github.com/dahlend/kete

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milleramp ◴[] No.44536010[source]
Is there a rule of thumb speed where an object is considered not from this solar system?
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ddahlen ◴[] No.44536065[source]
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).

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1. icehawk ◴[] No.44536512[source]
> 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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2. ddahlen ◴[] No.44536619[source]
Oort cloud comets are so distant that they are only weakly gravitationally bound to the solar system. When they come in and we see them, they have enough energy to go back out to the extreme distances. Minor nudges from the big planets are enough to cause them to become ejected from the solar system (ecc>1). This can lead to the whole "one and done" thing.