Evidence for Earth magnetospheric tail associated phenomena at 3100 RE

Abstract

Examination of Pioneer 7 NASA Ames Research Center plasma analyzer data obtained in February 1977 at ∼3100 RE, downstream from the earth in the vicinity of the expected extended geomagnetic tail indicate that tail related phenomena may have been observed. These observations are characterized by intermittent intervals of extremely low levels of plasma ion flux. Corresponding Prognoz 5 Space Research Institute plasma ion data obtained in the vicinity of earth indicate typical solar wind flux levels and a relatively steady character to the solar wind during this time. These recent Pioneer 7 observations in the vicinity of the expected geomagnetic tail at ∼3100 RE are consistent with our earlier Pioneer 7 observations in September 1966 at ∼1000 RE and our Pioneer 8 observations in January 1968 at ∼500 E and represent the most extended positive observational information of the extended nature of the geomagnetic tail. These measurements suggest that at times Jupiter's magnetosphere may have tail associated phenomena extending to distances of ∼10 AU downstream from the planet. These measurements also raise the possibility that at times comets may have tail associated phenomena extending downstream from the visible tail.