Planetary Binary Orbits
Date: Prior to 1993
Is a binary orbit possible? I mean, if there was another planet
where would Earth be in six months of roughly the same mass, would it affect
Earth's orbit any? Are there examples of binary orbits (not suns) in the
cosmos? Any intelligent response would be appreciated.
I think the movie was titled "Journey to the Far Side of the
Sun". If currently accepted theories of planetary formation are correct, it
is extremely unlikely that "twin" planets would form on opposite sides of the
sun. These theories say that tiny "planetesimals" condensed out of the
primordial solar dust cloud; over time, some of these bumped into their
neighbors and stuck together. Eventually some of these became big enough to
attract others gravitationally, and ultimately one which became the Earth
dominated, sweeping out all of the matter in the vicinity of its orbit.
Unfortunately, we have (so far) only one solar system to test the theories on.
How do we know there is not a second Earth on the opposite side of the Sun?
Well, Earth's orbit is not perfectly circular; it is an ellipse, and the Earth
does not move at a constant speed in its orbit, so even if at a given time
there were an Earth-sized body in the same orbit directly opposite the Earth,
it would not stay directly opposite. I do not know if such a planet would ever
be visible (it might always be lost in the glare of the sun), but its presence
would still show up in the gravitational perturbations it would exert on the
other planets (including the Earth).
There was an old sci-fi movie about a twin planet to the Earth
locked into orbit exactly opposite the Earth. I cannot think of any reason
why that would not be possible. There is no evidence of such a planetary
system, but then there is no evidence of any planetary system outside our own;
but that should change after the Hubble Space Telescope data is analyzed.
Click here to return to the Astronomy Archives
Update: June 2012