The Pioneer 8 Earth-Moon encounter



In the May 7, 1991, Eos, F. M. Neubauer and K.-H. Glassmeier took up the cause of “historical correctness” in a comment on the conarticle by F. Fanale (Eos, November 20, 1990, p. 1803) about the Galileo encounter with the Earth-Moon system in December 1990. The 1991 article pointed out that Fanale was incorrect in claiming that Galileo was to perform the first “encounter by a spacecraft from deep space with the Earth-Moon system,” since Giotto encountered the Earth in July 1990.

While this event certainly invalidates the claim of primacy for the Galileo spacecraft, it does not award it to Giotto. The October 1987 Journal of Geophysical Research contains a paper by the late Fredrick L. Scarf describing results from the Pioneer 8 encounter with the geomagnetic tail in April and May 1985. At that time, the Pioneer 8 solar arrays' long exposure to space had so degraded the power levels of the spacecraft that Scarfs plasma wave instrument was the only one that could be operated.