Comment by ddahlen
2 days ago
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?
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.