Direct observation of lunar pick-up ions near the Moon

Measurements made with the Suprathermal Ion Spectrometer (STICS) on the WIND spacecraft during 17 lunar fly-bys which took place between 1995 and 1997 allow the direct observations of lunar pick-up ions (PUI's) on the earthwards side of the Moon as close as 17 lunar radii. The composition measurements reveal an O+, an Al+, Si+ and possibly a P+ component.