The shape of our solar system's orbits.

  • Context: High School 
  • Thread starter Thread starter PrincePhoenix
  • Start date Start date
  • Tags Tags
    Orbits Shape Solar
Click For Summary

Discussion Overview

The discussion centers around the shapes of planetary orbits in our solar system, comparing them to those of extrasolar planets. Participants explore whether the orbits are elliptical or circular, and the implications of eccentricity in these orbits.

Discussion Character

  • Debate/contested
  • Technical explanation
  • Exploratory

Main Points Raised

  • Some participants assert that the orbits of the planets in our solar system are very nearly circular for 7 out of 8 planets, while others like Mercury and Pluto have more elliptical orbits.
  • It is noted that a circle is a special case of an ellipse, leading to discussions about whether elliptical orbits can be considered "round."
  • A participant presents calculations showing the average eccentricity of the solar system's planets compared to extrasolar planets, suggesting that the solar system's orbits are less eccentric.
  • Concerns are raised about whether the data reflects the actual nature of extrasolar planet orbits or biases from detection methods.
  • Some participants speculate about the implications of having multiple planets with low eccentricities in the solar system and whether this is a unique characteristic.
  • A debate arises regarding the claim that all orbits are spiral, with participants challenging this assertion and discussing the reference frames of orbital paths.
  • There are mentions of gravitational effects and other forces that could influence orbital shapes, but these points remain speculative.

Areas of Agreement / Disagreement

Participants express differing views on the nature of orbits, with some agreeing that the solar system's orbits are mostly circular while others challenge the uniqueness of this characteristic. The discussion remains unresolved regarding the implications of eccentricity and the nature of orbits in general.

Contextual Notes

Participants acknowledge the limitations of their calculations and assumptions, particularly regarding the observational biases in detecting extrasolar planets and the influence of various forces on orbital paths.

PrincePhoenix
Gold Member
Messages
116
Reaction score
2
What's the shape of the planets orbiting the sun in our solar system according to this website
http://www.chacha.com/question/what-is-the-shape-of-orbit-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?
 
Last edited by a moderator:
Astronomy news on Phys.org
PrincePhoenix said:
What's the shape of the planets orbiting the sun in our solar system according to this website
http://www.chacha.com/question/what-is-the-shape-of-orbit-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?
 
Last edited by a moderator:
I mean "round" not "rounded"?
 
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?&munit=&runit=&punit=&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.)
 
Last edited:
Note that a circle is just a special case of an ellipse: all orbits are elliptical.
 
russ_watters said:
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.
 
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.
 
But does that tell us about the extrasolar planet orbits or about the extrasolar planet detection mechanism?
 
Vanadium 50 said:
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.
 
  • #10
DaveC426913 said:
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.
 
  • #11
talk2envy said:
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.
 
  • #12
talk2envy said:
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.
 
  • #13
twofish-quant said:
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.
 
  • #14
All orbits in this universe are spiral.
 
  • #15
Are you just kidding, or are you seriously saying all orbits are spiral?
 
  • #16
YES. What one isn't?
 
  • #17
Tom Kull said:
YES. What one isn't?

Why shouldn't we report you as a troll? Your statements are unjustified. Do you want to give us more information, or do you just want an argument?
 
  • #18
All satalites move about primaries that are moving also. If the positions of the two bodies were ploted over time These plots would resemble a spiral. Sorry I live in a universe that has at least four dimentions not two.
 
  • #19
Tom is thinking that, from an external reference point, the elliptical orbit coupled with proper motion of the system results in a helical path, which he is then mistakenly calling spiral.

Tom, the path a planet follows is entirely dependent on the observer's frame of reference. You have chosen the FoR that is from a body in relative motion along the axis of the solar system in which the planet is orbiting. By saying all orbits are [helical] you've mistakenly assumed a FoR reference that is somehow more valid than any other.
 
  • #20
Hard to tell what he's thinking. He might be including some very small braking effects, such as the emission of gravitational radiation (which always happens), or Poynting-Robertson drag (which is a larger effect in most circumstances but requires the orbiting body to be warmed by the body it's orbiting so that it emits radiation. Or he might just be being silly - who knows?
 
  • #21
pervect said:
Hard to tell what he's thinking. He might be including some very small braking effects, such as the emission of gravitational radiation (which always happens), or Poynting-Robertson drag (which is a larger effect in most circumstances but requires the orbiting body to be warmed by the body it's orbiting so that it emits radiation. Or he might just be being silly - who knows?
No, he doesn't mean planets are spiraling inwards; he means they're following a helix. See his post 18.

He's still under a misapprehension; but not as bad as it seems.
 
  • #22
I am not sure of the distintion between helik and spiral. positions are plotted with time as well as x,y and z but I suppose that is hard to depict on paper without using a spirograph.
 
  • #23
I took Tom's remark as a light hearted jest to remind us that all of our discussions on eccentricity revolve (pun intended) around a heliocentric perspective. (Or should that be barycentric?) I thought it was quite whimisical and was amused by graal's spontaneous hostile reaction to a suspected troll.

If science isn't fun you remove half the reason for doing it.
 
  • #24
Ophiolite said:
I took Tom's remark as a light hearted jest to remind us that all of our discussions on eccentricity revolve (pun intended) around a heliocentric perspective. (Or should that be barycentric?) I thought it was quite whimisical and was amused by graal's spontaneous hostile reaction to a suspected troll.

If science isn't fun you remove half the reason for doing it.

Must've put my "cranky pants" on that day. But it's a rather trollish thing to say isn't it?
 
  • #25
qraal said:
Must've put my "cranky pants" on that day. But it's a rather trollish thing to say isn't it?
Well, it's only trollish if he knew it were controversial. I don't think he realizes how far from reality his preconception of relative motion is.
 
  • #26
  • #28
I'm pretty sure Tom is correct about this. Most orbits (especially naturally occurring orbits) follow a spiral... I'm not 100% certain I'm going to go look it up right now.

EDIT: The orbits of the planets ALL follow a spiral. I.e. Earth is moving towards the sun albeit a very small amount it still does. So does Mars and a few other planets. A few of the planets are moving away from the Sun such as Venus and Mercury.
 
Last edited:
  • #29
Since the distance is changing extremely slowly, it is overly nitpicky to bring up the spiraling here. It is not helpful to the OP.
 
  • #30
russ_watters said:
Since the distance is changing extremely slowly, it is overly nitpicky to bring up the spiraling here. It is not helpful to the OP.

Yeah this is true, I wasn't bringing up to address the OP but just to add some credibility to Tom because a few people seem to be acting pretty negatively against his comment.
 

Similar threads

High School Does Time Pass at Different Rates on Other Planets?
  • · Replies 19 ·
Replies
19
Views
2K
High School Planetary Orbits - Elliptical or Wavelike?
  • · Replies 10 ·
Replies
10
Views
2K
High School How Does a Massive Planet's Orbit Around the Sun Appear?
  • · Replies 6 ·
Replies
6
Views
2K
Undergrad New Developments In The Search For Planet X
  • · Replies 2 ·
Replies
2
Views
3K
High School Terminology for motion in the solar system, ecliptic maybe?
  • · Replies 13 ·
Replies
13
Views
2K
Stargazing Planetary orbits -- Why do planets orbit at same “level”?
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Astronomy in a Simple Solar System
  • · Replies 122 ·
5
Replies
122
Views
9K
High School Question about the solar system and gravitational forces
  • · Replies 10 ·
Replies
10
Views
2K
Undergrad Evidence for existence of a 9th Planet in the solar system
  • · Replies 15 ·
Replies
15
Views
3K
High School Has Earth Lost Its Status as a Planet?
  • · Replies 24 ·
Replies
24
Views
3K