Pluto's rotation

Fluctuations in Pluto's light led to the conclusion that it rotates on its axis once every 6.4 days. This provided new insights into Pluto's rotational behavior and surface characteristics.
 Walker and Hardie United States 1955 Pluto's rotation

Fluctuations in Pluto's light led to the conclusion that it rotates on its axis once every 6.4 days. This provided new insights into Pluto's rotational behavior and surface characteristics.