The planet Saturn from Pioneer 11, September 1979.
© National Aeronautics & Space Administration / Science & Society
Pioneer 11, launched by NASA on 6th April 1973, returned the first close-up pictures of the ringed planet Saturn. The results, although visually spectacular, were rather disappointing from a scientific point of view. The second largest planet in the Solar System, Saturn was first observed through a telescope by Galileo in 1610, but its rings were not identified until 1659, by Christiaan Huygens. It is a gas giant similar in atmospheric composition to Jupiter, and rotates very quickly, causing it to appear oblate (flattened at the poles). The rings are composed of ice and ice-coated dust and rock. Their origin and formation are not precisely understood, but it seems that tidal effects caused by some of Saturn's moons play a role in maintaining their structure.