page_title: Rings of Saturn
section_title: Propeller moonlets
hierarchical_section_title: Rings of Saturn / A Ring / Propeller moonlets
caption_attribution_description: First moonlets discovered in Saturn's A ring
context_page_description: The rings of Saturn are the most extensive ring system of any planet in the Solar System. They consist of countless small particles, ranging in size from micrometers to meters, that orbit about Saturn. The ring particles are made almost entirely of water ice, with a trace component of rocky material. There is still no consensus as to their mechanism of formation. Although theoretical models indicated that the rings were likely to have formed early in the Solar System's history, new data from Cassini suggest they formed relatively late.
  Although reflection from the rings increases Saturn's brightness, they are not visible from Earth with unaided vision. In 1610, the year after Galileo Galilei turned a telescope to the sky, he became the first person to observe Saturn's rings, though he could not see them well enough to discern their true nature. In 1655, Christiaan Huygens was the first person to describe them as a disk surrounding Saturn.
context_section_description: In 2006, four tiny "moonlets" were found in Cassini images of the A Ring. The moonlets themselves are only about a hundred metres in diameter, too small to be seen directly; what Cassini sees are the "propeller"-shaped disturbances the moonlets create, which are several km across. It is estimated that the A Ring contains thousands of such objects. In 2007, the discovery of eight more moonlets revealed that they are largely confined to a 3,000 km belt, about 130,000 km from Saturn's center, and by 2008 over 150 propeller moonlets had been detected. One that has been tracked for several years has been nicknamed Bleriot.
caption: Location of the first four moonlets detected in the A ring.
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