Re:Another Interstellar Object Detected in the Solar System
by davidmurdoch on Wednesday September 11, 2019 @10:12PM
(#20947098)
It it not at all possible for an interstellar object to be captured into a stable solar orbit?
Re:Another Interstellar Object Detected in the Solar System
by greglindahl on Wednesday September 11, 2019 @10:50PM
(#20947376)
Not without interacting with a 3rd body, such as Jupiter.
Re:Another Interstellar Object Detected in the Solar System
by ars on Wednesday September 11, 2019 @11:20PM
(#20947595)
Or, apparently, if it crosses an event horizon, although I've never properly understood how that works. (Explanations I've found typically just say: "All paths from a black hole are toward the black hole."
Re:Another Interstellar Object Detected in the Solar System
by greglindahl on Wednesday September 11, 2019 @11:42PM
(#20947727)
Most things flying towards a black hole don't cross the event horizon thanks to angular momentum.
Stars tend to get torn apart, go into the accretion disk, and then eventually fall in. But we don't have a big black hole in the solar system.
Re:Another Interstellar Object Detected in the Solar System
by DavidSJ on Thursday September 12, 2019 @01:19AM
(#20948254)
For present purposes the Newtonian approximation suffices, and in Newtonian gravity there are no black holes and no event horizons.
Re:Another Interstellar Object Detected in the Solar System
by lojack on Wednesday September 11, 2019 @10:28PM
(#20947220)
Captured into a stable orbit, sure, but it will never have an eccentricity of 0 (circular). The limit can approach zero, but will never be equal to it. Even the planets don’t have a circular orbit FWIW.
Re:Another Interstellar Object Detected in the Solar System
by _kst_ on Thursday September 12, 2019 @01:08AM
(#20948194)
An interstellar object cannot be captured into a stable orbit unless some other force (such as Jupiter's gravity) acts on it.
Orbits are time-symmetric, so an interstellar object being captured into a stable elliptical orbit would be equivalent to an object in a stable elliptical orbit escaping the Solar System (again, ignoring other influences).
Re:Another Interstellar Object Detected in the Solar System
by tempestn on Thursday September 12, 2019 @02:41AM
(#20948666)
Is that true of comets as well? It seems conceivable to me that the sun could spin it around such that the comet's off-gassing could reduce its speed and allow it to be captured. Obviously unlikely, and highly dependent on conditions (in particular incoming velocity) but possible.
Re:Another Interstellar Object Detected in the Solar System
by lojack on Thursday September 12, 2019 @09:52AM
(#20951431)
If you're ignoring all other influences then there is no such thing as interstellar objects. By definition, every object in a two body system are gravationally bound to each other.
An interstellar object cannot be flying by slowly enough to enter a circular orbit. If it were, it would already have been in a circular orbit. Trajectories can be extrapolated both into the future and into the past. It has enough momentum to escape the Solar System if and only if it came from outside the Solar System.
This assumes the only interaction is the gravitational pull between the Sun and the object. A close approach to Jupiter, for example, might slow an incoming object into an elliptical orbit, or speed a Solar System object into a hyperbolic escape trajectory.