Can two planets share the same orbit without catastrophic consequences?

In summary: Not by the current definition of a planetBut by that definition, exoplanets are not planets either.There is an exception to this rule, however. The L4 and L5 points of any planet, which lay 60 degrees behind and 60 ahead of the planet, tend to collect objects ( case in point, Jupiter's Trojan asteroids). So in these two particular instances, the planet has not cleared the neighborhood of its orbit.So the question is: would a Planetary sized object be stable at either of these points.This paper: http://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=8093&context=etd_theses
  • #1
Rifat amin
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can two planets share the same orbit
 
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  • #3
DrClaude said:
Not by the current definition of a planet

But by that definition, exoplanets are not planets either.
 
  • #4
Doesn’t the definition apply only to our solar system? It doesn’t say anything about exoplanets, either way.
 
  • #5
Here is the definition: A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Exoplanets are not planets.
 
  • #7
Two plaets could have the same orbit, but stability might be a problem.
 
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  • #8
Vanadium 50 said:
Here is the definition: A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Exoplanets are not planets.

(c) has cleared the neighborhood around its orbit.
There is an exception to this rule, however. The L4 and L5 points of any planet, which lay 60 degrees behind and 60 ahead of the planet, tend to collect objects ( case in point, Jupiter's Trojan asteroids). So in these two particular instances, the planet has not cleared the neighborhood of its orbit.

So the question is: would a Planetary sized object be stable at either of these points.
This paper: http://scholarworks.sjsu.edu/cgi/viewcontent.cgi?article=8093&context=etd_theses

Seems to conclude that it would be possible to have a body at either the L4 or L5 points for the Earth, that has a mass comparable to that of the Moon. For a gas giant like Jupiter, some 333 times more massive than the Earth, I don't foresee a problem with maintaining a body of planetary mass ( satisfying parts (a) and (b) of the definition. at its L4 or L5 point.

Whether such body could be technically called a "planet" by IAU nomenclature is another question. I assume it would depend on whether or not having a single mass of that size there would disrupt the collection of other bodies or gather them into orbit around itself.
 
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  • #9
vela said:
According to the IAU site, that's the "definition of a planet in the Solar System." It makes no claims about objects outside our solar system.

https://www.iau.org/static/resolutions/Resolution_GA26-5-6.pdf
It does seem reasonable to me that the definition could be applied for any solar system.
A planet is in orbit around a star and has cleared it's orbit of other substantial objects.
Anything less than that is an asteroid, or a moon
 
  • #10
Janus said:
For a gas giant like Jupiter, some 333 times more massive than the Earth, I don't foresee a problem with maintaining a body of planetary mass ( satisfying parts (a) and (b) of the definition. at its L4 or L5 point.

Whether such body could be technically called a "planet" by IAU nomenclature is another question. I assume it would depend on whether or not having a single mass of that size there would disrupt the collection of other bodies or gather them into orbit around itself.
I'm going to go out on a limb and say the OP is probably not after a semantic answer and this [great] technical answer will satisfy him/er.
 
  • #11
Rifat amin said:
can two planets share the same orbit

There are some weird orbits

The bean shape we have companion orbiting the sun 365 day orbit. Cruithne is not a planet but one could have the same orbit.

Lagrange4/Lagrange5

Binary planets

The Pluto Charon system is a great example. The IAU does not consider Charon to be a planet. The IAU does not consider Pluto to be a planet either. Also Eris-Dysnomia.

There is a lot more if you are asking what "can" happen with organized help. You can use any regular plane geometry figure. equalateral triangle, square, pentagon, hexagon etc. They are highly unstable and unnatural. You can elliptical orbits with the shapes so they pulse in and out. Or you can add a retrograde set.
 
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  • #12
Vanadium 50 said:
Here is the definition: A celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit.

Exoplanets are not planets.
Does the classification affect the Physics involved?
 
  • #14
nikkkom said:
Sure they can.

Saturn has two moons in coorbital arrangement. Same is possible for planets.

https://en.wikipedia.org/wiki/Co-orbital_configuration
It's not as simple as the two satellites following the same path for ever though, is it? They interact, That sort of mutual gravitational effect also means that geostationary satellites need to be spaced a significant distance apart to minimise the amount of fuel needed to cancel their mutual effect and keep them stationary in the same orbital spot.
 
  • #15
Before devling into the question of co-orbing planets, let's consider a better definition of a planet than the offical IAU one given. It seems a better definintion would be that a planet is a natural object in space that is spheroidal in shape and is not undergoing fusion in its interor and therefore is not self luminous. Size, compostion, orbital parameters, and location have no bearing. The added stuff about having "cleared its neighborhood", what ever that means, is limiting and confusing and should be discarded.

As for whether two planets can share the same orbit, considering that a planet is a natural spheroidal, none self luminous object in space, I can think of no good reason why not. We have examples in the Solar System, although they involve moons and small irregular natural satellites. Tethys and Dione, which orbit Saturn, share their orbits respectively with Calypso and Telesto and with Helene and Polydeuces, located at either the leading or trailing Lagrange point. It may be speculation, but perhaps somewhere in the Galaxy, orbiting some star, there's a planet the size of Mars, lead or trailed by one the size of Mimas or Enceladus, or one the size of Earth lead or trailed by one the size of Europa. Seems possible if conditions were right during formation. We'll have to wait and see.
 
  • #16
sophiecentaur said:
It's not as simple as the two satellites following the same path for ever though, is it?

Basically they do. The periodic change in their orbits' radius is less than the diameters of the satellites.
 
  • #17
nikkkom said:
Basically they do. The periodic change in their orbits' radius is less than the diameters of the satellites.
And they have to be at Lagrange points for this? That has now made things clearer for me.
 
  • #18
sophiecentaur said:
And they have to be at Lagrange points for this? That has now made things clearer for me.

In this case, no. They are in mutual "horseshoe" orbits. One is in a lower orbit and thus is faster, it very slowly approaches another, they they exchange momentum (since they attract), and now the leading object is in a lower orbit and thus moves faster, and thus runs away. Counterintuitive.
 
  • #19
nikkkom said:
In this case, no. They are in mutual "horseshoe" orbits. One is in a lower orbit and thus is faster, it very slowly approaches another, they they exchange momentum (since they attract), and now the leading object is in a lower orbit and thus moves faster, and thus runs away. Counterintuitive.

I have read about horseshoe orbits but to they really pass that close to each other? The diagrams don't seem to suggest that.
 
  • #20
sophiecentaur said:
I have read about horseshoe orbits but to they really pass that close to each other? The diagrams don't seem to suggest that.

They come close enough to start feeling a weak mutual attraction. Which is not really very close for planetoid-sized objects.
 
  • #21
nikkkom said:
They come close enough to start feeling a weak mutual attraction.
The inverse square law operates at all distances and, given the same mutual situation and being put out in deep space, they would have a highly elliptical but 'regular' orbit, wouldn't they? If it were not for the mutual attraction, over the whole period, they wouldn't have the horseshoe orbit.
 
  • #22
sophiecentaur said:
If it were not for the mutual attraction, over the whole period, they wouldn't have the horseshoe orbit.

Mutual attraction does work over the the whole time, but most of the time it's insignificant. When Epimetheus and Janus are, say, 90 degrees apart along the orbit, their attraction is _very_ tiny. What matters at that moment is that one of them is in a lower orbit and thus moves faster. Therefore, eventually they will come close. And _then_ mutual attraction starts to matter.
 
  • #23
nikkkom said:
, their attraction is _very_ tiny.
Oh yes. Definitely but 'enough' and I would say that it always matters - even when it's hard to measure. AS I commented; if it were not there, there would be no horseshoe.
 
  • #24
nikkkom said:
Sure they can.

Saturn has two moons in coorbital arrangement. Same is possible for planets.

https://en.wikipedia.org/wiki/Co-orbital_configuration

By definition, no.
Jupiter is in 1:1 resonance with Hector. Hector is so small compared to Jupiter - slightly over 200 km diametre against 140 000 km of Jupiter - that Hector is an asteroid, Jupiter has cleared its orbit and is a planet.
Jupiter is also in a resonance with Saturn, but this is 5:2 one. The mass ratio of Jupiter to Saturn is slightly over 3.
The mass ratio of Ceres to Vesta is also close to 4 - I think it is actually bigger than the mass ratio of Jupiter to Saturn.
Not only is Vesta an asteroid - but Ceres also is.

There is no physical reason why Saturn could not orbit in 1:1 resonance with Jupiter. However, in that case, Saturn would be an asteroid - and Jupiter would also qualify as asteroid, through not clearing its orbit. Mars and Mercury would still be planets, on the other hand.
 
  • #25
snorkack said:
By definition, no.
...
There is no physical reason why Saturn could not orbit in 1:1 resonance with Jupiter. However, in that case, Saturn would be an asteroid - and Jupiter would also qualify as asteroid

Thank you for explaining us IAU's definition of word "planet" for the 1000th time.

By IAU definition, there are no planets anywhere except Solar System. Not that IAU are idiots, no - they simply limited their task to a tractable one: "let's have a definition of what planet is _in our system_, not in any conceivable star system in all ~200 billion observable galaxies".

Therefore I'm wrong: coorbital planets are not possible. I hope this statement satisfies resident definition lawyers here.

For people who are interested in discussing less lawyery topics, let's continue talking about coorbital planets, twin planets (Pluto/Charon, Earth/Moon etc), Lagrange planets etc.
 
  • #26
Would a genuine coorbital planet pair show up in Kepler data?

For a stable Lagrange point, like Trojans or several Saturn satellites (though all small), it would show up - regular eclipses separated by exactly 1/6 the total orbital period.
 
  • #27
A very long time ago Earth shared at least part of an orbit with a Mars sized body called Theia. That did not end well. The two collided leaving behind an embarrassingly large large reminder [the moon] of the price inherent to orbital promiscuity. This appears to be all but inevitable when large objects routinely cross, much less share orbits. An exception may apply in the unlikely event both bodies are nearly identical in mass. Even then, perturbations by neighboring bodies may disrupt orbital resonance leading once again to a giant impactor scenario. This is probably why the IAU threw the 'cleaned out' provision into their definition of a planet. A body that has not cleaned out its orbital path is probably considered too immature to qualify as a fully fledged planet..
 

1. Can two planets share the same orbit without catastrophic consequences?

No, it is not possible for two planets to share the same orbit without catastrophic consequences. This is because the gravitational pull of each planet affects the other, causing their orbits to become unstable and eventually collide.

2. What if the two planets have similar masses?

Even if the two planets have similar masses, they will still experience gravitational pull from each other which can disrupt their orbits. Additionally, the presence of other celestial objects such as moons or asteroids can also affect the stability of the shared orbit.

3. Are there any examples of two planets sharing the same orbit?

No, there are no known examples of two planets sharing the same orbit in our solar system or in other observed planetary systems. This is because the laws of physics and gravity make it highly unlikely for such a scenario to occur naturally.

4. Can artificial intervention make two planets share the same orbit?

In theory, it is possible for artificial intervention to make two planets share the same orbit. However, it would require precise calculations and constant adjustments to maintain the stability of the shared orbit. It is not a feasible or practical option for planetary systems.

5. What if the two planets are in a binary system?

In a binary system, two planets can orbit around a common center of mass and appear to share the same orbit. However, they are not truly sharing the same orbit as each planet is still affected by the gravitational pull of the other. These systems are carefully balanced to prevent catastrophic consequences and are relatively rare in the universe.

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