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View Full Version : How did Neptune catch Triton?



Tom Mazanec
2004-May-23, 01:38 PM
Triton is supposed to be a captured planetoid from the Kuiper Belt, right? But I thought objects heading for a planet either impact or go off in a hyperbolic trajectory. How did Neptune snag Triton?

harlequin
2004-May-23, 01:59 PM
Triton is supposed to be a captured planetoid from the Kuiper Belt, right? But I thought objects heading for a planet either impact or go off in a hyperbolic trajectory. How did Neptune snag Triton?

They can also go in ellipses as well. In Newtonian mechanics, if we only consider these two objects and only consider gravity then Triton's path would have to fit a conic section. These includes circles and ellipses as well as parabolas and hyperbolas.

Tom Mazanec
2004-May-23, 04:14 PM
But I thought the object has to go through its previous point, so an object coming from infinity has to return to infinity. That's why satellites need to be "put" in orbit when they reach space, or else they would return to Earth. I know orbits must be conic sections, but how do you change a parabolic or hyperbolic one into an elliptical or circular one? If there was a large third boddy, wouldn't the body still be in the solar system? Isn't Pluto in a resonance with Neptune such that it never was near it? Or am I phrasing this badly? I don't see how a trajectory which was not closed around Neptune initially becomes closed so nicely (if retrograde).

aurora
2004-May-23, 04:21 PM
If there was a large third boddy, wouldn't the body still be in the solar system? Isn't Pluto in a resonance with Neptune such that it never was near it?

Not necessarily and yes.

And by "large" we might only need something the size of another Kuiper Belt object. It could now be in the Oort cloud, or it could have been ejected from the solar system, or it could have been flung into the Sun or Jupiter or even Neptune. When the solar system was young, there was a lot more material out there, the asteroid belt and Kuiper belt just hint at what was originally in orbit around the Sun.

I'm wondering how long it would take Triton to settle into its current orbit if its original orbit had been more elliptical?

Meteora
2004-May-26, 10:49 AM
Curiosity question:

Do elliptical orbits become circular over time (and yes, I know that circles are special forms of ellipses!)? If so, how?

ToSeek
2004-May-26, 01:23 PM
Curiosity question:

Do elliptical orbits become circular over time (and yes, I know that circles are special forms of ellipses!)? If so, how?

If there are any drag forces operating at all (and there always are), they will be greatest at periapsis (closest point), when the object is moving the fastest, and least when the object is at apoapsis. This would tend to circularize the orbit over time.

(There may be other factors operating as well, but that's the only one I can think of.)

Meteora
2004-May-26, 01:29 PM
Ah... makes sense. Thanks for the reply!

aurora
2004-May-26, 04:48 PM
If there are any drag forces operating at all (and there always are), they will be greatest at periapsis (closest point), when the object is moving the fastest, and least when the object is at apoapsis. This would tend to circularize the orbit over time.

(There may be other factors operating as well, but that's the only one I can think of.)

Tidal interactions between moons could change the orbits too, I think. I'm thinking of Earth's moon moving away from Earth as momentum is transferred, and also the interactions between Jupiter's Galilean moons.

I'm guessing that there could be a chaotic affect until things get sorted out that could change the shape of a particular orbit.

Andreas
2004-May-26, 09:53 PM
There's also swing-by maneuvers to consider. Well, since it wasn't controlled by someone perhaps it wouldn't be called maneuver or even swing-by, but you get the idea.

To be specific: An object crossing in front of the planet's orbital path will transfer energy to the planet and thereby brake down -- and maybe get caught into an orbit, if it gets slow enough. At least, that's how I understand it.