OBSERVATIONS Of the collisions of the fragments of comet Shoemaker-levy 9 with Jupiter provided an unprecedented opportunity to probe the depths of the planet’s atmosphere, Images taken by the Hubble Space Telescope revealed circular rings surrounding five of the impact sites(1). The rings were observed for up to 2.5 hours after the impacts and spread at a constant velocity of 450 m s(-1). There are three types of disturbance that might explain these observations : acoustic waves trapped at the tropopause temperature minimum(2), gravity waves propagating vertically and horizontally in the stratosphere(3), and gravity waves trapped in a stable layer which acts as a horizontal waveguide and is located within the hypothesized tropospheric water cloud(4). Here we show that only the last of these phenomena fan match the speed and relative amplitude of the observed waves, with the requirement that the impacts were deep and the stability of the trapping layer is large. The origin of the stable layer is still uncertain, but if it is produced by moist convection in the water cloud, then the ratio of oxygen to hydrogen on Jupiter must be surprisingly large-approximately ten times that on the Sun.