Welcome, Guest. Please Login.
Gravity Simulator
11/19/17 at 00:47:46
News: Registration for new users has been disabled to discourage spam. If you would like to join the forum please send me an email with your desired screen name to tony at gravitysimulator dot com.
Home Help Search Login


Pages: 1
Send Topic Print
Retrograde extrasolar planets (Read 1988 times)
EDG
Ultimate Member
*****


oh, crumbs!!!

Posts: 611
Gender: male
Retrograde extrasolar planets
04/13/10 at 19:11:34
 
http://www.universetoday.com/2010/04/13/dropping-a-bomb-about-exoplanets/
 
Quote:
To account for the new retrograde exoplanets an alternative migration theory suggests that the proximity of hot Jupiters to their stars is not due to interactions with the dust disc at all, but to a slower evolution process involving a gravitational tug-of-war with more distant planetary or stellar companions over hundreds of millions of years. After these disturbances have bounced a giant exoplanet into a tilted and elongated orbit it would suffer tidal friction, losing energy every time it swung close to the star. It would eventually become parked in a near circular, but randomly tilted, orbit close to the star. A dramatic side-effect of this process is that it would wipe out any other smaller Earth-like planet in these systems, says Didier Queloz of Geneva Observatory.

 
It sounds like the Kozai mechanism may be to blame here, but how would that make the orbits retrograde?
Back to top
 
 

(formerly known as Mal)
View Profile WWW   IP Logged
frankuitaalst
Ultimate Member
*****


Great site

Posts: 1507
Gender: male
Re: Retrograde extrasolar planets
Reply #1 - 04/14/10 at 11:58:13
 
Is weird indeed . I wonder what percentage of the orbits are really retrograde .  
Kozai implies that the planet comes very close to the host star several times . It is possible that on one of its close encounters it rounds the star from the left instead as from the right due to minor disturbances in the far point.  
I've seen this already in one of my simulations ...
So the planet may become retrograde without doubt .  
What I don't get intuitive is that the orbit then again becomes circular , but here I guess the hydrodynamic drag may play a role after millions of years .
Back to top
 
 
Email View Profile   IP Logged
EDG
Ultimate Member
*****


oh, crumbs!!!

Posts: 611
Gender: male
Re: Retrograde extrasolar planets
Reply #2 - 04/15/10 at 19:50:03
 
I'm a bit fuzzy on how Kozai works (I shouldn't be, given all those sims I ran a few years ago here, but my memory has faded Smiley ), but IIRC it's basically that inclination gets bigger at eccentricity's expense, and vice versa right? Could the inclination get so big that the orbit ends up being tilted more than 180 relative to where it was, so that the planets look like they're going the wrong way round the star? And then maybe it stays that way because the same circumstances that tipped the orbit to > 180 don't happen again?
Back to top
 
 

(formerly known as Mal)
View Profile WWW   IP Logged
frankuitaalst
Ultimate Member
*****


Great site

Posts: 1507
Gender: male
Re: Retrograde extrasolar planets
Reply #3 - 04/15/10 at 23:00:39
 
Quote from Mal on 04/15/10 at 19:50:03:
I'm a bit fuzzy on how Kozai works (I shouldn't be, given all those sims I ran a few years ago here, but my memory has faded Smiley ), but IIRC it's basically that inclination gets bigger at eccentricity's expense, and vice versa right? Could the inclination get so big that the orbit ends up being tilted more than 180 relative to where it was, so that the planets look like they're going the wrong way round the star? And then maybe it stays that way because the same circumstances that tipped the orbit to > 180 don't happen again?

The flip from prograde to retrograde I once observed occured at moderate inclination , but at a very high eccentricity .  
Lets say the planet once is in a situation of about 50 inc and eccentricity near 1 . It then rounds the star very close , goes then to its far point where it has almost zero velocity . At that point it may happen that it chooses to go to the star again to the "left" instead of to the "right" , resulting in a flip . Such "instability" is more likely in multiple planet systems.
Back to top
 
 
Email View Profile   IP Logged
EDG
Ultimate Member
*****


oh, crumbs!!!

Posts: 611
Gender: male
Re: Retrograde extrasolar planets
Reply #4 - 05/24/10 at 15:33:45
 
That Kozai guy is at it again Wink
 
http://www.universetoday.com/2010/05/24/wild-and-crazy-multi-planetary-system-su rprises-astronomers/ : I'll bet you anything that the crazy orbits are all down to the influence of the companion star.
 
Also, http://www.astronomy.com/asy/default.aspx?c=a&id=9889 : Kozai with planets?  
 
I think it's funny that people just seem to be starting to realise how important the Kozai mechanism is...
Back to top
 
 

(formerly known as Mal)
View Profile WWW   IP Logged
frankuitaalst
Ultimate Member
*****


Great site

Posts: 1507
Gender: male
Re: Retrograde extrasolar planets
Reply #5 - 05/25/10 at 10:05:57
 
funny indeed .  
I whished I could ever make a retrograde system from "scratch" . Never succeeded till now , not even in the 30 planetary formation runs I've made so far recently  cry
Back to top
 
 
Email View Profile   IP Logged
Pages: 1
Send Topic Print