View Full Version here: : Planet Orbiting the Wrong Way

14-08-2009, 05:23 PM

WASP-17, a transiting Hot Jupiter which is about 1000ly away, is apparently orbiting in a regtrograde orbit. The article says it was possibly caused by a gravitational interaction between it and another planet at some time in its early history.

Well, that planet's fate is sealed...it'll eventually fall in towards the star and vapourise.

14-08-2009, 10:07 PM
Calling all physicists! Am I correct in assuming that if it was the only planet in orbit about this Sun, that the orbit would be reasonably stable. However, another outer planet in the system would create gravitational drag and have the effect of retarding angular momentum so that eventually the retrograding planet would spiral towards the Sun.
Because of distance, frame-dragging should be fairly negligible on the planet.

Regard, Rob.

15-08-2009, 12:08 AM
No...frame dragging will have little to no effect. It's too small an effect, even with large bodies like a star. Only in very dense objects like neutron stars and black holes will it become appreciable. In this case, given the way the planet is orbiting, the tidal effects generated between the star and the planet will eventually brake the orbital motion of the planet and it'll spiral into the star. If there were an outer planet in some sort of orbital resonance with the inner one, except orbiting in a prograde motion, that would also cause tidal braking to the inner planet. There'd also be a good chance that the outer planet's orbit maybe adversely affected as well because of the same effect between both planets.

15-08-2009, 01:11 PM
Wouldn't tidal forces at the planet's distance be fairly negligible?

Regards, Rob

15-08-2009, 03:20 PM
No, they'd be horrendous....remember, it's a Hot Jupiter and it's orbiting close enough to have the day side toasting at a balmy 2380 degrees C!!:eyepop:

Not much closer and the planet would get ripped apart....it wouldn't be far from the star's Roche Limit as it is.