Voyager 2 at Uranus: Grain impacts in the ring plane

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Abstract
During the Uranus ring plane crossing at 4.57 Uranus radii, the PRA instrument aboard Voyager 2 recorded a characteristic intense noise extending 104 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.