| Telescope: | Canada-France-Hawaii telescope, f/36 focus |
| Date: | August 12, 1995 from 11h 33m to 12h 30m (UT) |
| Instrument: | University of Hawaii 13-actuators adaptive optics system. |
| Wavelength: | H-band and J-band |
| Total exposure: | Each image is made of 10 to 15 30s exposures |
| Scale: | Each image is 19"x12" |
| Orientation: | North is up - East is left |
| Observers: | Claude Roddier, François Roddier, J.E. Graves, M.J. Northcott |
From top to bottom and left to right: time sequence of images of Saturn's E ring obtained on Aug 12, 1995 (from 11:30 to 12:30 UT) in the H band (top row and bottom left image) and in the J band (middle row). Time intervals are about 10 minutes. The bottom right image is an average of all the others. Note the nearly horizontal streak on the left side of the dark vertical cursor. Starting at the cursor on the first image, the streak right edge moves leftward on subsequent images. Assuming Keplerian motion, the streak appears to be produced by an arc of particles moving on an orbit close to that of Enceladus, but slighlty more inclined. The orbital phase of the sharp right edge is about 75 degree ahead of that of Enceladus, i.e. close to that of its Lagrangian point. Note the foreshortening of the arc as it approaches its maximum elongation. It also appears to be a transcient phenomenon since the intensity of the arc decreases by a factor of two during the observations and no such structure was observed at the same orbital position two days before. Our most likely explanation is that a large block of ice previously ejected by Enceladus collided with ice fragments trapped on the satellite orbit near its L4 Lagrange point. The collision occured 5 to 6 hours before the observations started, and produced a rapidly expanding cloud of small ice particles. We estimate the total mass of small particles to be of the order of 100 tons. If such collisions occur at an average rate of once a month, the amount of generated small particles is sufficient to maintain the E ring in its present state.
