How possible is it that there is another planet similar to ours that is on the exact same orbit as us, except it is always on the opposite side of the sun.
Would be able to tell if there was? Are we certain there isn’t?
I figure if it is on the same orbit and it was always on the other side of the sun, how would we know? The could calculate the wobble of the sun to see if it is being effected by the gravity of another planet, but have they? Is there a concept I am missing here?
… Other than proper spelling and punctuation I mean. :rolleyes:
Dontcha think that some of the probes that NASA has sent out to the far reaches of the solar system would have picked something up? Or is this a strictly hypothetical question?
In the mid to late 70s they did a movie about that…an astronaut leaves earth and ends up on this twin planet on the far side of the sun, where visual and radio communications effectively shielded the existence of each planet from the other (Sorry, don’t know the name of the movie).
Anyway, a few years back NASA instructed the VOYAGER 1 probe was instructed to photograph the solar system as a whole. Its position was high above the solar system’s orbital plane, so one could see all the planets. The photo was grainy, but in Earth’s orbit, there is only ONE Earth.
enolancooper
OT, but does anyone know where to get a copy of that photo? I would loooove a large print made for our rec room. Kind of a family portait. I get a warm, fuzzy feeling just thinking about it.
While it might be difficult to differentiate the effects of gravity between an object directly opposite the sun and the earth that unique geometry does not exist with respect to Venus, Mars, and the many smaller bodies observed over the centuries by astronomers. The hypothetical Counter Earth would be detectable by indirect measurement. In fact, the effect would have been noticed first, and the hypothesis of a body in orbit, together with its inferred mass would have been put forth, and tested.
Eventually, NASA would have been encouraged to examine the position in opposition with a telescopic probe on one or more of its out of Earth orbit missions.
Of course they were probably too busy faking the data for the “Moon Landing.”
The problem is that the other planet would have to have EXACTLY the same orbit that earth does. If there was even a whisper of a difference our orbits would get out of sync in the 4.5 billion years the earth has been orbiting the sun. Actually, there are two moons of Saturn (or was it Jupiter) that have almost identical orbits. When one catches the other, they do a little flip and switch orbits. Now THAT would be kinda fun.
The planet Pluto was discovered because its existence was predicted, based on calculations of Uranus’s orbit. After Uranus was discovered, a few years of observations led scientists to the idea that either there was yet another planet, or that Newton’s law of gravity was wrong.
So if a tiny planet so far away could be discovered this way, an Earth-sized object so close-in would have been detected long ago, before any space probes were sent up.
Yup, that’s it exactly. Actually, it’s effects would be noticeable pretty quickly! Venus and Mars would be strongly affected.
The movie, BTW, was “Journey to the Far Side of the Sun”, done by Gerry Anderson (who later did Space:1999). Cool flick, if really really silly. Everything on the counter Earth was left-right reversed, so he didn’t know he wasn’t on Earth until he couldn’t find the light switch in the bathroom. 
This link addresses the specific question. I’ve heard estimates of as little as thirty years before a planet on the far side of the sun would be dragged so far out of position by the gravities of other planets that it would be visible to Earth astronomers.