Wednesday, June 9, 1999 Published at 19:04 GMT 20:04 UK
Dust cloud surrounds Jupiter's moon
An artist's impression of Galileo orbiting Jupiter
By BBC News Online Science Editor Dr David Whitehouse
A cloud of dust grains has been discovered around Ganymede, Jupiter's largest moon.
Astronomers made the measurements using the Heidelberg dust detector on board the Galileo spacecraft which has been in orbit around Jupiter since December 1995.
The dust cloud is believed to have formed when high velocity meteoroids from space struck the surface of Ganymede knocking off tiny grains.
Some of the dust stays in the moon's vicinity and some migrate to add to the ring around Jupiter.
Scientists hope that the new research will lead to a better understanding of the processes that form the ring systems which surround all the giant planets in our solar system.
The dust was detected when the Galileo spacecraft flew within a few hundred kilometres of Ganymede. The highly sensitive Dust Detection System onboard Galileo measured the dust as it impacted on a gold target.
There is one grain in every 20 metres cubed, which is interesting scientifically but no danger to the Galileo spacecraft.