Goals: Pioneer 9 was the fourth in a series of solar orbiters designed to study, from widely separated points in space on a continuing basis, interplanetary phenomena such as the Sun's magnetic field, the solar wind and solar and galactic cosmic rays.

Accomplishments: Pioneer 9 gathered valuable data on the properties of the solar wind, cosmic rays and interplanetary magnetic fields. In conjunction with Pioneers 6, 7, and 8, the spacecraft formed a ring of solar-weather stations, spaced approximately along Earth's orbit.

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