Rotation of mercury

Microwave data indicated Mercury's rotation period is approximately 59 days, disproving the belief that it always faced one side towards the Sun. This discovery revealed Mercury's dynamic rotational behavior.
 Rolf Buchanan Dyce, Gordon H. Pettengill United States 1965 Rotation of mercury

Microwave data indicated Mercury's rotation period is approximately 59 days, disproving the belief that it always faced one side towards the Sun. This discovery revealed Mercury's dynamic rotational behavior.