Saturday, 21 September 2013

The origin of mini-jets in Saturn's F Ring.

The F Ring is the outermost and thinest of Saturn's rings. It was discovered by the Pioneer 11 Spacecraft in 1979, and has been studied by NASA's Cassini Probe since it's arrival at Saturn in 2004. The F Ring is only a few hundred kilometers across, and is apparently constrained by the presence of two 'shepherd moons', Prometheus and Pandora, which orbit just inside and outside it. Unlike the other rings of Saturn the F Ring appears to be very active, constantly producing mini-jets of material which project up to 200 km outside the ring's main structure.

Two theories have previously been put forward to explain this, firstly that the jets could be the result of perturbations in the ring caused by the passage of the shepherd moons, and secondly that they might be the result of collisions between larger objects within the ring itself. 

In a paper published on the online arXiv database at Cornell University Library on 12 September 2013, Nicholas Attree, Carl Murray, Gareth Williams and Nicholas Cooper of the School of Physics and Astronomy at Queen Mary University of London discus the result os a study in which they examined 889 mini-jets in images captured by the Cassini Probe, 32 of which were imaged more than once.

Cassini images of Saturn's F Ring; (a) complex features re-projected in a radius/longitude frame to the same scale, showing numerous small mini-jets, and (b) a complex mini-jet. Attree et al. (2013).

Attree et al. could find no evidence that the distribution of the mini-jets correlated to the movement of the shepherd moons; the distribution of the mini-jets was apparently random with regard to the position of the moons. Many of the jets appeared to be reasonably long-lived; one was seen to move half way around the ring in a series of images. This supports the idea that the jets are emerging from larger objects within the ring, that are occasionally damaged in collisions.

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