Jupiter Had Temporary Moon for 12 Years

"... only the fifth captured comet to be identified ..." - as I understand it, that's in our time (i.e. very recent history). Which suggests that this sort of this has happened perhaps many millions of times during the history of the solar system.

How did the comet get free ? I'm gueesing it wasn't because anyone payed the ransom. Did it get smaller by melting a bit so there wasn't enough gravitation force to keep it orbiting ? I can't think of any other reason. I'm writing this after only 1 coffee, so nobody take the **** out of any apparent stupidity in my question/answer !

If you drop a cannon ball and a feather in a vacuum on earth they fall together (with the same acceleration); toss them sideway slightly, remove the earth and replace it with a point mass at it's centre and the cannon ball and feather will just start an elliptical orbit with your hands at the outer edge and the point mass at one of the focal points. An orbit is an orbit doesn't matter how massive the object in orbit is.

The above is correct; below is bullshit speculation.

I suspect that it's possible for an object to fall into an orbit which is partly about the Sun and partly about the planet (a sort of extended slingshot). The comet's speed relative to Jupiter may not exceed the escape velocity when Jupiter is on one side of the Sun, but, does exceed it when Jupiter is on the other side of the Sun (think waltzers).

EDIT Jupiter's year is just less than 12 earth years, but, I can still imagine a sort of erratic temporary orbit which would work.

OK, I think I see what your saying ; If the international space station split in two, the 2 bits would keep orbiting just the same (?).

Your hypothesis (which seems to make sense) is that the overall pull on the comet from Jupiter + Sun (or whatever planet) changed during those years, and got to a point where it escaped. Have I understood you right ? This is probably basic stuff, but my brain just won't wrap itself around it yet !

If the international space station split in two, the 2 bits would keep orbiting just the same (?).

Exactly.

I don't think the overall pull has to "change". I think there are just some orbital interactions which naturally produce a sort of clover leaf pattern which kind of synchs. and un-synchs. with the orbit of Jupiter. Don't forget the comet's original orbit is an ellipse about the Sun; its temporary orbit about Jupiter was probably a very eccentric (and time variant) ellipse.

Here's a comet simulation site:-

http://www.windows.ucar.edu/tour/link=/comets/comet_model_interactive.html

shame they don't include interactions with the planets.

Ta for the clarifications and link (which I'll have to check later). Did you see the thread I posted about some software called "Universe Sandbox" ? Chuffing brilliant ! This is all a bit outside my province, but that software looks great - it could probaly provide the means to simulate exactly what this comet did. I haven't had the time to fully explore the program, but for those interested in such stuff it looks top rate. The chap who wrote it even came along an offered to take questions from people (now that's what I call good). I'll try return to this later - got to visit the dentist ().

As passingtongreen said, there are lots of other moons in orbit around Jupiter to screw with the orbit of this new moon. There are probably many more "temporary" orbital trajectories there than there are "permanent" ones.

Thanks, bhaknkii.

This kind of begs the question ; "Are there other planets with moons/comets that will evetually escape them?". As pointed out earlier (Hendrick/Randell, not sure) this can't be a unique phenomana. Maybe not in our solar system, but perhaps elsewhere. Could our next 'visitor' be such an object ? In terms of objects aproaching Earth, I've no idea if one type poses more risk than the other. Iced up rock, or just plain rock, I can't see how it makes much difference (except that one might melt more before impact). It a bit OT, but any thought's ? Are there any exisisting satellite moons in our solar system that could potentially be swung out of orbit ? I'm sure Planetary Physicists have it all mapped out, but it still makes me wonder.

I would assume so. There's no reason to think that the solar system is particularly static. Our own moon moves a bit further away from the earth each year and will eventually escape.

Cheers - if you're into this kind of stuff, check this out ; http://cr4.globalspec.com/thread/38090/Universe-Sandbox

Very cool bit of softaware. Although it may sound like I'm pimping it a bit, I have no connection. I simply stumbled upun it and thought it very cool.

Jupiter has other moons which exert a gravitational force. It could be a slingshot around one or more of these.