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Kepler 11 6 planets system (Read 13641 times)
EDG
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Re: Kepler 11 6 planets system
Reply #15 - 02/07/11 at 12:56:25
 
Yeah, that's why I hate the term "dwarf". Really, it means "Main Sequence star", but because people are so used to hearing about red dwarfs and orange dwarfs (and because of the builtin connotations of the word itself) it's often assumed that the star must be small. It gets even sillier when you realise that A V stars should be called "white dwarfs" (that name's already taken of course) and B stars should be "blue dwarfs", despite the fact that they're more massive than the sun and also are larger in radius! Smiley
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Re: Kepler 11 6 planets system
Reply #16 - 02/07/11 at 13:55:37
 
Well, my defense is always that I'm a bit of an idiot but an idiot interested in space stuff. I have to take solace in the fact that most Guardian readers would read an article about Kepler 11 and decide that this is teeny weeny, so its planets can be close in to something rather cool. Hell they're liberals, they probably don't like the term anyway but demoting our beloved sun into a dwarf is not cricket. I wonder if working astronomers are aware of this.    
 
So, how do these planets keep their atmospheres, they've been bashing round for billions of years, they should be just chunks of rock by now.
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Re: Kepler 11 6 planets system
Reply #17 - 02/07/11 at 15:04:11
 
Quote from Bob on 02/07/11 at 13:55:37:
Well, my defense is always that I'm a bit of an idiot but an idiot interested in space stuff. I have to take solace in the fact that most Guardian readers would read an article about Kepler 11 and decide that this is teeny weeny, so its planets can be close in to something rather cool. Hell they're liberals, they probably don't like the term anyway but demoting our beloved sun into a dwarf is not cricket.

 
Um, let's leave the puerile (and irrelevant) political namecalling out of it, shall we?
 
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I wonder if working astronomers are aware of this.

 
Most working astronomers don't really care. And "Yellow dwarf" (annoying as it is) has been used for a long time to describe our sun, so it's hardly "demoting it into a dwarf".
 
 
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So, how do these planets keep their atmospheres, they've been bashing round for billions of years, they should be just chunks of rock by now.  

 
Same way that the planets in our own solar system have kept their atmospheres for 4.6 billion years - their gravity keeps it there.
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Re: Kepler 11 6 planets system
Reply #18 - 02/07/11 at 22:45:27
 
"Um, let's leave the puerile (and irrelevant) political namecalling out of it, shall we?"
 
Politically, I consider myself to be on the liberal left, so my comment was hardly name-calling.
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Re: Kepler 11 6 planets system
Reply #19 - 02/08/11 at 02:27:02
 
Quote from Bob on 02/07/11 at 22:45:27:
Politically, I consider myself to be on the liberal left, so my comment was hardly name-calling.

 
Either way, it's still not relevant here.
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Re: Kepler 11 6 planets system
Reply #20 - 02/08/11 at 07:06:49
 
I've been following this discussion for a while, and just wanted to add a few points.
 
First, I'm pretty confident that we can dismiss the idea of a massive body orbiting in a nearly perpendicular plane to the others. The reason I say this is because if this was the case, the chances that we'd have SIX planets in nearly exactly the same plane becomes vanishingly small. Try it: Add a MJ planet to the system at 0.8 AU with inclination 0° and let the system run for a few hundred millennia. The inclinations of the planets will seem almost random.
 
The other point I wanted to address is the eccentricity of these orbits. I will have to follow up on this, but I believe that planets discovered by transit have an "assumed zero" until further observations based on some other method (i.e. NOT transits). The reason is because we only have ONE POINT (actually, it's a very short arc, but for practical purposes it can be considered a point) on the orbit where we can make observations. Even with repeated observation of the transits, we're still looking at the SAME POSITION in the orbit. Eccentricity can not be determined with only data from a single point.
 
There are three variables we can measure based on the transit: (1) The PERIOD of the orbit (obviously, based on repeated regular intervals between transits), (2) the CROSS-SECTIONAL AREA of the planet (based on how much the star's apparent magnitude decreases during the transit), and (3) the LENGTH OF TIME of the transit, which when combined with the period allows us to calculate the inclination, but ONLY if we assume a very small eccentricity and some diameter of the star based on mass and spectral class.
 
In order to calculate the eccentricity, we'd either need data from (at least) one other point on the orbit, or accurate data on the planet's velocity (relative to the star) at the known point. Transits of planets can give us neither (eclipsing binary stars, on the other hand, readily give us a second data point), but redshift data can fill the velocity gap.
 
Additional Note: While writing this, I was running the modified system as described above with an additional planet. It didn't even take 2000 years before the system was catastrophically disrupted, leaving only 11b, 11g, and the hypothetical "11h" after the collisions and ejections resolved.
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Re: Kepler 11 6 planets system
Reply #21 - 02/08/11 at 07:25:02
 
Quote from Bob on 02/07/11 at 13:55:37:
So, how do these planets keep their atmospheres, they've been bashing round for billions of years, they should be just chunks of rock by now.

 
This is actually an interesting question, because light gasses should be swept away by solar wind. That's why our own inner planets aren't surrounded by vast hydrogen clouds, after all.
 
If I had to guess, I'd say the gas giants in Kepler 11 have very strong magnetic fields. I'd also assume that the star has lower stellar winds than our own sun due to its lower mass.
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Re: Kepler 11 6 planets system
Reply #22 - 02/08/11 at 09:38:40
 
The massive body, if such exists, won't be at ninety degrees to the orbital plane of the planets now but it would have been a long time ago. It's now at about 88 degrees like the planets in the sim. We make it a dwarf of about 0.05 solar masses, at round about the 200 a.u. mark. Then we should have a Kozai cycle of around 6 billion years for those close in planets. The closer in the less their mass seems to matter.  
 
http://journals.cambridge.org/action/displayAbstract?fromPage=online&aid=426 3492
 
I did watch a little u tube movie but I can't remember what my search terms were, so can't find it again. Does it work or is it a fudge? I don't know but it's certainly interesting.
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Re: Kepler 11 6 planets system
Reply #23 - 02/08/11 at 10:40:14
 
Here's an animation of the Kepler 11 system  
The animation lasts about 15 years.  
One can easily see the plansts perturbing each other , except the outermost one .  
The innermost planets b and c orbits interact strongly . This is not visible in this animation because the timeframes are multiples of the orbital periods .  
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Animation_Kepler11.gif
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Re: Kepler 11 6 planets system
Reply #24 - 02/08/11 at 14:14:36
 
Quote from Bob on 02/08/11 at 09:38:40:
The massive body, if such exists, won't be at ninety degrees to the orbital plane of the planets now but it would have been a long time ago. It's now at about 88 degrees like the planets in the sim. We make it a dwarf of about 0.05 solar masses, at round about the 200 a.u. mark. Then we should have a Kozai cycle of around 6 billion years for those close in planets. The closer in the less their mass seems to matter. 

 
I'm still not seeing why you think there's another massive body, and specifically one that was at 90 degrees to the orbital planet but isn't now.  
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Re: Kepler 11 6 planets system
Reply #25 - 02/08/11 at 14:45:28
 
It's not my idea, and frankly I don't know what to make of it. As I understand it, we have a a binary star system with the planets of the primary star at ninety degrees to the dark companion. Over time with the Kozai mechanism  they rotate 180 degrees. One might think that that's okay but it seems that resonances can occur which disrupt the whole system and pull the planets closer in to the primary.
 
The nearest thing that I can think of, that perhaps bears some relationship to this. is gimbal lock. Having said that, it's just a hunch, I could be way off with that idea.
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Re: Kepler 11 6 planets system
Reply #26 - 02/08/11 at 15:05:13
 
Quote from Bob on 02/08/11 at 14:45:28:
It's not my idea, and frankly I don't know what to make of it. As I understand it, we have a a binary star system with the planets of the primary star at ninety degrees to the dark companion. Over time with the Kozai mechanism  they rotate 180 degrees. One might think that that's okay but it seems that resonances can occur which disrupt the whole system and pull the planets closer in to the primary.

The nearest thing that I can think of, that perhaps bears some relationship to this. is gimbal lock. Having said that, it's just a hunch, I could be way off with that idea.  

 
Yes, but who's saying that there's a binary companion? There's no need for one there at all to explain anything.
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Re: Kepler 11 6 planets system
Reply #27 - 02/09/11 at 01:40:03
 
I did give one link but there are quite a few articles out there, most on the Kozai effect with only one massive planet on close orbit. I expect people are lining up their ducks and waiting on more data. Two rather rough and ready camps, one thinks that the planets were formed further out and migrated in, the other that massive planets can form close in to their primary and keep their atmospheres.  
 
Who cares, it will eventually all come out in the wash. I was hoping though that someone who knows the app would run a sim of a multiple planet with the Kozai effect  taken into account. Simply because it would be a fun thing to do  Smiley Just use the little java script thingy to get some graphs set up. At first blush, it looks as though the Kozai cycle starts in the millions of years, minima to minima, with each planet having it own cycle but later the cycle seems to get longer for all of the planets together, as they come in closer.
 
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Re: Kepler 11 6 planets system
Reply #28 - 02/09/11 at 11:15:06
 
Quote from frankuitaalst on 02/08/11 at 10:40:14:
Here's an animation of the Kepler 11 system
The animation lasts about 15 years.
One can easily see the plansts perturbing each other , except the outermost one .
The innermost planets b and c orbits interact strongly . This is not visible in this animation because the timeframes are multiples of the orbital periods .

If this body was there at 90° inclination , then one can ask : how did it get there ? AFAIK this situation also doesn't correspond with standard formation models.
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Re: Kepler 11 6 planets system
Reply #29 - 02/09/11 at 12:05:10
 
Quote from Bob on 02/09/11 at 01:40:03:
I was hoping though that someone who knows the app would run a sim of a multiple planet with the Kozai effect  taken into account.

 
It can - just create the system in the gravsium as normal (it's been done before here, several times). The Kozai mechanism comes out of it naturally, if you've set it up appropriately.  
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