orbits

[Kaziarl]

Ok, so here's a question. It's for my fan fic, but I consider this to be a real science type of question, so I'm putting it here.

I know we've done a good job at mapping our solar system by now, so I'm pretty sure there isn't one, but i want to know if it's theoretically possible to have a second planet, similar in size and mass, following our same orbital path.

This second earth would be on the opposing point of the path, with the sun directly in the middle.

So two things,

1. Is it possible? However unlikely, I simply want to know if it would be able to have a stable orbit.

2. What sort of effects might there be? Gravitational effects on neighboring planets? on the sun? would one planet eventually "catch up" to the other?


Another scenario to consider, could you have a planet orbiting the other direction from the others in the system?

 

[Maurice]

I googled your question and found several sits that discuss it.

http://www.astro.uu.nl/~strous/AA/en/antwoorden/planeten.html#v165

See Scientific Analysis section here: http://en.wikipedia.org/wiki/Counter-Earth

 

[Neopeius]

1. Is it possible? However unlikely, I simply want to know if it would be able to have a stable orbit.

As pointed out in links below, no. That planet would be detectable by other means. It was a trope of science fiction well into at least the 70's, however.

2. What sort of effects might there be? Gravitational effects on neighboring planets? on the sun? would one planet eventually "catch up" to the other?

It would definitely affect other planets. As for it being perturbed, the anti-Earth position is also known as the third "Lagrange Point" and is highly unstable precisely because it can be perturbed by other planets. Far more stable are the fourth and fifth Lagrange Points, also known as Trojan Points, which are 60 degrees ahead and trailing a planet's orbit.

In fact, there are big families of asteroids in Jupiter's orbit, and in Saturn's moon system, which is like a little solar system, the moon Dione has a little companion in one of it's Trojan points.

Obviously, if there were a planet in one of Earth's Trojan Points, we'd have seen it. There may well be higher concentrations of interplanetary dust in them, though. It is a topic of scientific interest.

Another scenario to consider, could you have a planet orbiting the other direction from the others in the system?

Propably, although its origin probably would be highly unusual. In the Neptunian system, the satellite Triton orbits backwards. It may well be a captured Kuiper Belt object.

 

[Kaziarl]

1. Is it possible? However unlikely, I simply want to know if it would be able to have a stable orbit.

As pointed out in links below, no. That planet would be detectable by other means. It was a trope of science fiction well into at least the 70's, however.

2. What sort of effects might there be? Gravitational effects on neighboring planets? on the sun? would one planet eventually "catch up" to the other?

It would definitely affect other planets. As for it being perturbed, the anti-Earth position is also known as the third "Lagrange Point" and is highly unstable precisely because it can be perturbed by other planets. Far more stable are the fourth and fifth Lagrange Points, also known as Trojan Points, which are 60 degrees ahead and trailing a planet's orbit.

In fact, there are big families of asteroids in Jupiter's orbit, and in Saturn's moon system, which is like a little solar system, the moon Dione has a little companion in one of it's Trojan points.

Obviously, if there were a planet in one of Earth's Trojan Points, we'd have seen it. There may well be higher concentrations of interplanetary dust in them, though. It is a topic of scientific interest.

Another scenario to consider, could you have a planet orbiting the other direction from the others in the system?

Probably, although its origin probably would be highly unusual. In the Neptunium system, the satellite Triton orbits backwards. It may well be a captured Kuiper Belt object.

Ok, so first of all if this is incoherent I apologize, I've been drinking. But As I see it, it is possible, albeit highly unlikely that a star system with an equal mass, and orbit planetoids would be existent in an opposite position to the main planet. I'm using earth as an example. But with all the wonderous things that we have seen with current science, however unlikely, is it theoretically possible.

 

[Forbin]

'Twas exactly the plot of this movie:
http://www.imdb.com/title/tt0064519/

 

[Ronald Held]

No way. that planet would perturb all of the other solar system bodies, and would have been detected due to mismodeling of measurements of planets versus the numerical modeling needed to create the ephemerides.

 

[sojourner]

The OP didn't care if it would have been detected or not. He asked if it was physically possible for it to exist.

 

[Neopeius]

Ok, so first of all if this is incoherent I apologize, I've been drinking. But As I see it, it is possible, albeit highly unlikely that a star system with an equal mass, and orbit planetoids would be existent in an opposite position to the main planet. I'm using earth as an example. But with all the wonderous things that we have seen with current science, however unlikely, is it theoretically possible.

Anything's possible. The best scenario would be some sort of capture situation. Maybe two stars come close to each other and one of the planets ends up around the other star.

It probably can't happen naturally, though. The spinning disc that coalesces into a star and its planets will be spinning one way and all of its planets will be going that way as well.

The OP didn't care if it would have been detected or not. He asked if it was physically possible for it to exist.

Since my post is apparently tl:dr, the answer is it could exist, but not for long.

 

[Kaziarl]

http://phet.colorado.edu/sims/my-solar-system/my-solar-system.swf

found this site. Don't know how scientifically accurate it is, but you can plot orbits based on size, speed, direction, and position.

Here's the value's I used:
Body 1- Mass 200 Position 0,0 velocity 0,0
Body 2- Mass 10, position 142,0 velocity 0,119
body 3- Mass 10, position -142,0 velocity 0,-119

They seem to follow each other pretty well, but adding another planet throws it out of whack.

 

[Ronald Held]

If you cannot detect it, how do you know that it exists?
Yes, current theories of inner planet accretion would clear out an annulus of material near the orbit of the biggest embryo.

 

[Kaziarl]

Ok, so i've been playing with the program on that site I posted here. So far as I can tell it is possible, but extremely unlikely, for two planets to follow the same path. For one, a third object in its own orbit, however small I made it on that program, threw the entire thing out of wack. Same thing with minute changes in mass, starting position, anything. So the odds are astronomically high.

As for the other question, an object orbiting the opposite direction, I couldn't get anything stable. Maybe a few dozen trips around the star, then the orbit would collaps and it would either collide with something, or get launched out of the system.

 

[Daedalus12]

1. Is it possible? However unlikely, I simply want to know if it would be able to have a stable orbit.

No at least not in the sense that you described. Yes eventuallly both planets will drift into a stable configuration but the two planets will also have different orbits around the sun.

2. What sort of effects might there be? Gravitational effects on neighboring planets? on the sun? would one planet eventually "catch up" to the other?

N-Body dynamics for N>=3 is quite complex. Without running a n-body simulation code I can't be sure all the details of the pertubations. But as I said before if an earth-sized mass suddenly appeared at any point in Earth's orbit both planets would start drifting to different orbits.

 

[Ronald Held]

I run N-body code, and just having that earth mass appear in its orbit will cause changes in the future positions/velocities of all of the other solar system bodies. Future meausrements will be inconsistent with current ephemerides such as DE418.