Voyager 2 at Uranus: Grain impacts in the ring plane

During the Uranus ring plane crossing at 4.57 Uranus radii, the PRA instrument aboard Voyager 2 recorded a characteristic intense noise extending 10 4 km perpendicular to the ring plane. This is interpreted as due to impact ionization of dust grains striking the spacecraft. The noise level is smaller by a factor ∼ 170 than the same kind of event recorded during Voyager 2 Saturn encounter just outside the G‐ring. The results indicate a maximum concentration of about 10 −9 cm −3 of grains larger than 1 µm with a scale height ∼ 150 km across the ring plane. The distribution is asymmetrical, extending farther on the sunlit side. The inferred geometric optical depth is of order 10 −8 .