Even if the Sun blocked its view from Earth, a Counter-Earth would have gravitational influence (perturbation) upon the other planets, comets and man-made probes of the Solar System. Researchers have detected no such influence, and indeed space probes sent to Venus, Mars and other places could not have successfully flown by or landed on their targets if a Counter-Earth existed, as the navigational calculations for their journeys did not take any putative Counter-Earth into account. Roughly speaking, anything larger than in diameter should have been detected.