Detecting Counter Earth
Date: Spring 2013
If there was something matching Earth's orbit behind the Sun, would we be able to detect it?
If the object were massive enough and depending on where it is relative to the Sun and planets, it would affect the orbital paths of all the other planets. It might also affect the wobble of the Sun (which is pulled in all directions by the planets). So there would be some indication of its presence, its orbit, and its mass. (This by the way is one of the techniques for detecting exoplanets.)
Depending on its position "behind" the Sun, the light from the object (even distant stars, as well as Mercury when it is behind the Sun) will curve around the Sun and may actually be directly observable during a solar eclipse. Einstein's General Relativity Theory predicts that massive objects (such as the Sun) can cause light to bend around it so that an object that is somewhat behind the massive object can still be seen.
Greg (Roberto Gregorius)
Good question! Detecting another object in the same orbit as we would be very difficult. There are Earth Trojans, asteroids that share our orbit , but they are almost impossible to find since the sun is always in the way. I believe we have found one or two of the many that probably exist.,
David H. Levy
Thanks for the question. In principle, it is possible to detect another orbit behind the Sun. One would have to analyze and model data for the positions of planets in the night sky.
I hope this helps. Please let me know if you have more questions.
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Update: December 2011