Observation of 7Be on the surface of LDEF spacecraft

THELong Duration Exposure Facility (LDEF), an orbiting unmanned satellite, was recently returned to Earth after almost six years in space. From radioactivity measurements, we have found significant quantities of the isotope⁷Be on the leading edge (but only on the leading edge) of LDEF. Although the absolute atmospheric concentration of ⁷Be needed to explain this detection is extremely small (10^-7 atoms cm^-3), its concentration at LDEF's altitude (310 km) must be several orders of magnitude higher than in the stratosphere below, where it is produced by cosmic-ray reactions with atmospheric nitrogen and oxygen nuclei. To explain the presence of ⁷Be on the surface of LDEF, it must first be rapidly and efficiently transported to high altitudes, and then adsorbed onto the surface of the spacecraft. Neither process had been expected. Our detection may therefore lead to the use of ⁷Be as an exo-atmospheric tracer, as well as to studies of surface interactions in space.