There are rumors that there is a planet between Mercury and Venus. How valid are these rumors and what are they based on?
The procession of mercury could not be fully accounted by newtons laws. The planet was not in between Venus and mercury but between Sun and mercury.
So astronomers thought that there is an unknown planet known As Vulcan orbiting the Sun between Sun and Mercury..Problem was finally solved after Albert Einstein introduced the theory of relativity
Picture credit ASA tufts edu,