The Cassini spacecraft has identified a faint, previously unknown ring circling the giant planet Saturn.
It appears to be composed of material blasted off the surface of two saturnian moons by meteoroid impacts.
The moons Janus and Epimetheus may be too small to hold on to dust kicked out by these impacts, so it escapes into space, spreading out into a ring.
The tenuous, wispy ring coincides with the orbits of these two moons, mission scientists noted.
Researchers expected meteoroid impacts on Janus and Epimetheus to kick particles off the moons' surfaces and inject them into an orbit around Saturn. But they were surprised to find such a well-defined ring at this location.
Cast in shadow
Scientists owe their discovery to a highly unusual event: a solar occultation which put Cassini in Saturn's shadow for 12 hours.
The longest occultation of the four-year mission allowed the spacecraft to scrutinise the rings as they were strongly backlit by the Sun.
The marathon event also allowed Cassini to observe Saturn's moon Enceladus sweeping through Saturn's outer E-ring, extending wispy, fingerlike projections.
These projections, which interact directly with the E ring, consist of tiny ice particles being ejected from geysers at the moon's south pole.
Cassini also cast its eyes in our direction. The spacecraft took a picture of Earth from nearly 1.5 billion km (930 million miles) away.
Earth appears as a pale blue orb and there is a feature in the image which could be our Moon.
During the latest observations, scientists once again saw the bright, ghost-like features called "spokes". These are transient, unexplained "disturbances" that streak across the main rings of Saturn.
Cassini entered into orbit around Saturn on 1 July 2004. Later that year, it released the piggybacked Huygens probe towards the planet's largest moon, Titan.
Huygens touched down on Titan on 14 January 2005, sending back data on the moon's atmosphere, weather and its surface.
The Cassini-Huygens mission is a cooperative project of the US space agency (Nasa), the European Space Agency (Esa) and the Italian Space Agency (Asi).
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