Who told you Mercury doesn't rotate? It spins once around on its axis every 59 days! In 1889, astronomer G.V. Schiaparelli's observations of dark features on the planet's surface seemed to establish that its day was 88 days long, however in the early 1960's radar pulses reflected from the surface were successfully detected, and by 1965, G. Pettengill and R. Dyce were able to unambiguously determine that it rotated once every 59.3 =/- 2.0 days using Doppler radar techniques. This has been improved somewhat to the current 58.65 +/- 0.01 day period.