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This natural colour image of the crescent of Saturn was taken by the Cassini spacecraft wide-angle camera on the 27th October, 2009, when it was approximately 2.2 million kilometres away.
The moon Mimas can be seen as a dark spot just above the rings.
The Image scale is 129 kilometres per pixel.

saturn271009b.jpg
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Credit NASA/JPL/Space Science Institute

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Title: A north-south difference in the rotation rate of auroral hiss at Saturn: Comparison to Saturn's kilometric radio emission
Authors: D. A. Gurnett, A. M. Persoon, J. B. Groene, A. J. Kopf, G. B. Hospodarsky, W. S. Kurth

Broadband whistler-mode emissions, commonly observed by the Cassini spacecraft at high latitudes in Saturn's magnetosphere at frequencies below about 100 Hz, have characteristics very similar to auroral hiss observed at high latitudes in Earth's magnetosphere. In contrast to terrestrial auroral hiss, which shows no obvious rotational modulation, Saturnian auroral hiss shows a very pronounced rotational modulation. We show that the rotation period of the auroral hiss is different in the northern and southern hemispheres, with a period of about 10.6 hours in the northern hemisphere and about 10.8 hours in the southern hemisphere. To within experimental error the rotation periods in the two hemispheres match the rotation periods of Saturn Kilometric Radiation, an intense radio emission generated along the auroral field lines at frequencies from about 20 to 500 kHz. These northsouth asymmetries have potentially important implications on how angular momentum is transferred from the planet to the magnetospheric plasma.

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Title: X-rays from Saturn: A study with XMM-Newton and Chandra over the years 2002-05
Authors: G. Branduardi-Raymont (Mullard Space Science Laboratory, University College London, UK), A. Bhardwaj (Vikram Sarabhai Space Centre, Trivandrum, India), R. F. Elsner (NASA Marshall Space Flight Center, Huntsville, AL, USA), P. Rodriguez (XMM-Newton SOC, Villafranca, Madrid, Spain)

We present the results of the two most recent (2005) XMM-Newton observations of Saturn together with the re-analysis of an earlier (2002) observation from the XMM-Newton archive and of three Chandra observations in 2003 and 2004. While the XMM-Newton telescope resolution does not enable us to resolve spatially the contributions of the planet's disk and rings to the X-ray flux, we can estimate their strengths and their evolution over the years from spectral analysis, and compare them with those observed with Chandra. The spectrum of the X-ray emission is well fitted by an optically thin coronal model with an average temperature of 0.5 keV. The addition of a fluorescent oxygen emission line at ~0.53 keV improves the fits significantly. In accordance with earlier reports, we interpret the coronal component as emission from the planetary disk, produced by the scattering of solar X-rays in Saturn's upper atmosphere, and the line as originating from the Saturnian rings. The strength of the disk X-ray emission is seen to decrease over the period 2002 - 2005, following the decay of solar activity towards the current minimum in the solar cycle. By comparing the relative fluxes of the disk X-ray emission and the oxygen line, we suggest that the line strength does not vary over the years in the same fashion as the disk flux. We consider possible alternatives for the origin of the line. The connection between solar activity and the strength of Saturn's disk X-ray emission is investigated and compared with that of Jupiter. We also discuss the apparent lack of X-ray aurorae on Saturn and conclude that they are likely to lie below the sensitivity threshold of current Earth-bound observatories. A similar comparison for Uranus and Neptune leads to the same disappointing conclusion.

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In the first video showing the auroras above the northern latitudes of Saturn, Cassini has spotted the tallest known "northern lights" in the solar system, flickering in shape and brightness high above the ringed planet.
The new video reveals changes in Saturn's aurora every few minutes, in high resolution, with three dimensions. The images show a previously unseen vertical profile to the auroras, which ripple in the video like tall curtains. These curtains reach more than 1,200 kilometres above the edge of the planet's northern hemisphere.

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Credit NASA/JPL


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New ring discovered around Saturn is the largest in the Solar system
Previously it was thought that the famous planet only had seven rings named A through to E and several faint unnamed rings.
However Nasa's Spitzer Space Telescope was able discover a new ring by picking up tiny particles of dust and ice using an infrared instrument.


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Saturn is rotating five minutes faster than previously thought, a fact that sheds new light on the planet's composition. Wave patterns in Saturn's clouds show that scientists have been using the wrong rotation rate for the planet, said Timothy Dowling, a planetary atmospheres researcher at the University of Louisville, who helped make the discovery.
The work by Dowling and his colleagues solves a long-standing puzzle regarding Saturn's winds and also offers clues to the planet's deep interior. All of the gas giants - Saturn, Jupiter, Uranus and Neptune - spin on their axes with well-defined rotation periods, just like the rocky planets. But with no solid surface features to track, measuring how long they take to make a complete spin has been a challenge.

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Saturn's Rotation
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Astronomers have struggled to determine the length of a day on Saturn because the gas giant has no fixed surface point to clock its rotation rate, but now they think they have a solution.
In a study reported today in the U.K. journal Nature, researchers used clues from the planet's weather to derive a new figure for its rotation rate, estimating Saturn's day at 10 hours, 34 minutes and 13 seconds.


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