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Structures leap from Saturn rings as equinox approaches

Posted: August 10, 2009

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A new moonlet and strange vertical structures are among the treasure trove of goodies revealed by the Cassini spacecraft as Saturn nears equinox.

A new moonlet has been detected in the B ring as Saturn approaches its 11 August equinox. Image: NASA/JPL/Space Science Institute.

Equinox is a twice-yearly event when the Sun lies directly above a planet's equator. For Saturn, this occurs every 15 Earth years and sees the Sun pass through the plane containing the giant planet's rings. The unique illumination geometry allows features to be discerned in unprecedented detail. As Saturn marches towards its 11 August equinox, the Sun's angle to the ring plane lowers, causing out-of-plane structures to cast long shadows across the rings' broad expanse, making them easy to detect.

Narrow, vertically extended structures in the F ring cast long shadows as a result of the unique illumination geometry provided during equinox. Image: NASA/JPL/Space Science Institute.

Among the spoils in the latest data sweep is a new moonlet identified in Saturn's thin B ring. The moonlet is located about 480 kilometres inward from the outer edge of the ring, its presence given away by a 41 kilometre long shadow thrown on the ring. The shadow length suggests the moon is roughly 400 metres across orbiting 200 metres above the ring plane.

This mysterious object is casting a shadow that stretches from the F ring across to the A ring. Image: NASA/JPL/Space Science Institute.

Cassini has also collected a series of images revealing shadows cast by mysterious vertically extended structures in the outermost F ring. In one image the shadow of a mystery object appears to have punched through the F ring, dragging material along its path. In another example, the shadow stretches across the Roche Division – a gap that separates the A and F rings – and appears on the A ring.

The Cassini Imaging Team are working to understand the origin of these structures and no doubt more structures will be revealed in the coming days.