1) The earth's orbit is not exactly circular. It is an ellipse, so, any companion planet following the exact same orbital path WOULD be visible at certain portions of the orbit.
2) The gravitational effects of that companion planet would be noticeable in the orbits of Mars and Venus, at least. There is no such effect noticed.
3) There have been numerous probes sent to other planets closer to and farther away from the sun. None of those have EVER discovered any evidence of that companion planet.
That idea has been around for dozens of years, if not more, and has been totally and thoroughly debunked. It is not physically possible for something to hide on the other side of the sun, Period, Full stop.
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wilhelm say: Planets created gravitational waves that affect other celestial bodies and such would have been noticed and noted by now.
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VITTORIO say: Hmm! Symmetry is not that common
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spot a say: It is a hypothesis as there is no proof at all. Also such a planet does not exist. It would have been detected several hundred years ago from its gravitational effects. This is how the tiny dwarf planet Pluto was found, from its minute effect on the gas giants at billions of km distance from earth
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someg say: You mean Counter Earth? That is a misnomer. The other planet is Earth and we are on Counter Earth.
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Joseph say: There is no other planet sharing the Earth's orbit.
A planet sharing the Earth's orbit, if it did exist, will exert its gravitational influence on the motion of other bodies in the Solar system which we could easily detect.
Moreover, we have been using gravity assists to send the space probes to Venus and Mercury. If a planet such as your dad believes exists was real, it's gravity would have affected the trajectory of those probes and the engineers planning the mission would have to account for it. The engineers did not account for such planet and yet the probes arrived safely at their destinations, This pretty much proves that the planet does not exist.
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