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image The shape of our solar system's orbits. Share It Thread Tools Search this Thread image
Old Nov7-09, 10:54 PM                  #1
PrincePhoenix

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The shape of our solar system's orbits.

What's the shape of the planets orbiting the sun in our solar system according to this website
http://www.chacha.com/question/what-...bit-of-planets
they are elliptical. But in a documentary (maybe history channel's "The Universe", but I'm not sure) I heard that our solar system is one of the few known systems with round orbits.Majority of the others have elliptical. So what's the truth?
 
Old Nov7-09, 11:39 PM                  #2
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Re: The shape of our solar system's orbits.

Originally Posted by PrincePhoenix View Post
What's the shape of the planets orbiting the sun in our solar system according to this website
http://www.chacha.com/question/what-...bit-of-planets
they are elliptical. But in a documentary (maybe history channel's "The Universe", but I'm not sure) I heard that our solar system is one of the few known systems with round orbits.Majority of the others have elliptical. So what's the truth?
Isn't an elliptical orbit not rounded?
 
Old Nov7-09, 11:56 PM                  #3
PrincePhoenix

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Re: The shape of our solar system's orbits.

I mean "round" not "rounded"?
 
Old Nov7-09, 11:57 PM       Last edited by DaveC426913; Nov8-09 at 12:03 AM..            #4
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Re: The shape of our solar system's orbits.

The truth is that for 7 out of the 8 planets the SS's orbits are very nearly circular.

Mercury's, Pluto's and Sedna's orbits are more elliptical.


Here is a list of all extrasolar planets currently known.
http://exoplanet.eu/catalog-all.php?...=&mode=5&more=
You can even sort on the eccentricity column (Ecc). Eccentricity is a ratio if ellipticality of the orbit (zero is perfectly circular.)
 
Old Nov8-09, 12:11 AM                  #5
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Re: The shape of our solar system's orbits.

Note that a circle is just a special case of an ellipse: all orbits are elliptical.
 
Old Nov8-09, 12:12 AM                  #6
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Re: The shape of our solar system's orbits.

Originally Posted by russ_watters View Post
Note that a circle is just a special case of an ellipse: all orbits are elliptical.
That's what I was trying to get at in my previous post I guess I should have worded it more like: Can't elliptical orbits be round?

Now that I've reread what I said before it does sound kind of funny haha.
 
Old Nov8-09, 12:25 AM                  #7
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Re: The shape of our solar system's orbits.

A quick calculation shows that the average eccentricity of our SS's 8 major planets is ~0.0606
while the average of the 345 extrasolar planets with known eccentricities is ~0.2181
or about 3.5 times more eccentric.
 
Old Nov8-09, 01:44 AM                  #8
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Re: The shape of our solar system's orbits.

But does that tell us about the extrasolar planet orbits or about the extrasolar planet detection mechanism?
 
Old Nov8-09, 02:02 AM                  #9
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Re: The shape of our solar system's orbits.

Originally Posted by Vanadium 50 View Post
But does that tell us about the extrasolar planet orbits or about the extrasolar planet detection mechanism?
No doubt that's a factor.

But there are about 55 or so planets whose eccentricity is listed as unknown. I did not include those ones. Since 'unknown' is explicitly listed, it was a reasonable assumption that the listed values are trustworthy enough for a rough calculation.

It is a big assumption, I grant.
 
Old Nov8-09, 02:24 AM                  #10
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Re: The shape of our solar system's orbits.

Originally Posted by DaveC426913 View Post
A quick calculation shows that the average eccentricity of our SS's 8 major planets is ~0.0606
while the average of the 345 extrasolar planets with known eccentricities is ~0.2181
or about 3.5 times more eccentric.
The average does not give the complete picture. If you run the data through a frequency analysis, about 1/3 of the observed eccentricities are less than 0.05 (approximately the solar system average) and around 2/3 are less than 0.2.

The above doesn't take the distance of an exoplanet from its star into account and its conceivable that planets within different AU ranges could show different means. Furthermore, and this is purely conjecture on my part, it is possible that exoplanets with larger eccentricities are the larger gas giants and thus easier to observe. The data may be inherently biased by our current observational limitations.

In any case, if 30% of the observed exoplanets match the solar system average, then the solar system cannot be considered to be that unique.
 
Old Nov8-09, 10:53 AM                  #11
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Re: The shape of our solar system's orbits.

Originally Posted by talk2envy View Post
The average does not give the complete picture. If you run the data through a frequency analysis, about 1/3 of the observed eccentricities are less than 0.05 (approximately the solar system average) and around 2/3 are less than 0.2.

The above doesn't take the distance of an exoplanet from its star into account and its conceivable that planets within different AU ranges could show different means. Furthermore, and this is purely conjecture on my part, it is possible that exoplanets with larger eccentricities are the larger gas giants and thus easier to observe. The data may be inherently biased by our current observational limitations.

In any case, if 30% of the observed exoplanets match the solar system average, then the solar system cannot be considered to be that unique.
That's why I said "quick calculation" rather than "exhaustive calculation".

But you're right. The OP's post states "... our solar system is one of the few known systems with round orbits. Majority of the others have elliptical."

...which is clearly not what the data is showing when analyzed more carefully than a simple average.
 
Old Nov8-09, 02:03 PM                  #12
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Re: The shape of our solar system's orbits.

Originally Posted by talk2envy View Post
In any case, if 30% of the observed exoplanets match the solar system average, then the solar system cannot be considered to be that unique.
It could be. If the you have 30% of the exoplanets match the solar system average, and the eccentricities are random, then the odds of have eight planets all with more or less round orbits is quite low. Apparently there is a resonance between Jupiter and Saturn that keeps the rest of the planets in line.

I've heard this discussed in terms of the anthropic principle. Why are solar system orbits rather round? Because if they weren't we wouldn't be seeing them.
 
Old Nov8-09, 11:53 PM                  #13
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Re: The shape of our solar system's orbits.

Originally Posted by twofish-quant View Post
It could be. If the you have 30% of the exoplanets match the solar system average, and the eccentricities are random, then the odds of have eight planets all with more or less round orbits is quite low.
True but only if the eccentricity of each exoplanet is determined independently.

Apparently there is a resonance between Jupiter and Saturn that keeps the rest of the planets in line.
This argument could actually extend to other systems. Current observations very likely detect the largest object(s) within an extrasolar system. And if 30% of those have low eccentricities, then its possible that other smaller objects within these systems will also be forced into circular orbits.
 
Old Nov12-09, 09:57 PM                  #14
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Re: The shape of our solar system's orbits.

All orbits in this universe are spiral.
 
Old Nov12-09, 10:08 PM                  #15
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Re: The shape of our solar system's orbits.

Are you just kidding, or are you seriously saying all orbits are spiral?
 
Old Nov13-09, 10:23 AM                  #16
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Re: The shape of our solar system's orbits.

YES. What one isn't?
 
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