Saturn’s rings are nearly edge-on to the Sun now, so that small features in the rings that would otherwise be invisible are revealed by the lengthy shadows they cast. A striking discovery was reported today by the Cassini imaging team of a shadow cast by a moonlet within Saturn’s dense B ring. The length of the shadow provides an unambiguous measurement of the size of this object at about 400 m in diameter. This is about 100 times larger than the largest typical ring particle, and about one-tenth the size of the smallest moons observed at Saturn. Because it resides within the rings, its existence may suggest that some form of limited accretion is occurring within the rings, or that it is a collisional shard of a larger moon. Either way, it and other objects like it that are being discovered in Cassini data hold valuable clues to the origin of the rings.
This image shows a small bright object in the outer portion of Saturn’s B Ring casting a shadow on the ring. The length of the shadow indicates the size of the moonlet is ~400 m across. See the imaging team’s web site at www.ciclops.org for more details.