Is Mercury closer than what and when?From the sun the plants are the following distances:Sun 0.0 AUMercury 0.4 AUVenus 0.7 AUEarth 1.0 AUMars 1.5 AUAsteroid Belt 2.8 AUJupiter 5.2 AUSaturn 9.6 AUUranus 19.2 AUNeptune 30.0 AUThe following observations can be made:Mercury is closer than Mars to the sunMercury is 0.6 AU from the Earth, Mars is 0,5 AU from the Earth so Mercury (at its closest) is 0.1 AU closer than Mars (at its closest) to Earth.When Mercury is furthest from Earth it is 1.4 AU away, Mars is 0.5 AU away at its closest so Mercury is 0.9 AU further away than Mars.