Parallel bands of clouds have long been seen in Earth-based observations of Jupiter, and the reddish area below the equator, the Great Red Spot, has been known to exist for more than 300 years. Spacecraft images from the Pioneer and Voyager missions have revealed details in the atmosphere that cannot be seen from Earth.

On March 2, 1972, Pioneer 10 was launched from the John F. Kennedy Space center to become the first spacecraft to venture into the outer solar system. Eleven months later, the spacecraft had successfully passed through the asteroid belt, and on December 3, 1973, came within 130,000 kilometers (80,800 miles) of the cloud tops of Jupiter.

Both Pioneer 10 and Pioneer 11, which encountered Jupiter a year later, had 11 scientific instruments and experiments designed to map magnetic fields and radiation in interplanetary space, and determine the atmospheric structure of Jupiter and Saturn. An additional magnetometer was added to Pioneer 1 1 to study high strength magnetic fields.

The Atmosphere of Jupiter

The Jovian atmosphere contains numerous belts and storm systems with wind speeds up to 400 kilometers per hour (250 miles per hour). Between the dark and light cloud zones, wind shear and turbulence create great rotating storm systems, best exemplified by the Great Red Spot.

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N ASA Press Release Image #P-21599
Changes in the upper atmosphere are apparent in images taken by Voyager 1 (left) and Voyager 2 (right). During the intervening four months, several of the storms shifted their positions relative to the Great Red Spot. The atmosphere consists of the colorless gases hydrogen and helium, and trace elements that rise from deep in the atmosphere provide the color variations seen in these Voyager pictures.