Brightness Variations in Saturn’s Satellite 1995S5

This sequence of 100 sec exposures taken with HST's Wide Field and Planetary Camera (WFPC2) in planetary mode on 10 August 1995 shows the newly discovered object 1995S5 (red arrows) moving in its orbit around the planet. As it moves further from Saturn, its brightness decreases appreciably. This brightness variation is more consistent with that expected for an elongated, opaque clump of ring material than for a satellite, leading to the suspicion that 1995S5 is in fact a ring arc rather than a previously undiscovered satellite. It is likely that it lies within the narrow, braided F Ring.

In addition to 1995S5, the larger satellites Mimas and Epimetheus are visible in each frame. Mimas is the bright object below the rings, and is seen partly shadowed by the rings in the first frame. In subsequent frames it is in full sunlight. Epimetheus is near the eastern ansa of the rings, moving slowly outward. In the last frame of the sequence tiny Pandora has emerged from Saturn's shadow about 2 arcsec from the planet's limb.

These images were obtained one to two hours before the Earth crossed Saturn's ring plane and an 8922 A methane band filter was used to reduce the scattered light from the planet. An average of several other frames has been subtracted from each image to remove the light from the edge-on rings, and so reveal any faint satellites.