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Title: Interior Models of Saturn: Including the Uncertainties in Shape and Rotation
Authors: Ravit Helled, Tristan Guillot

The accurate determination of Saturn's gravitational coefficients by Cassini could provide tighter constrains on Saturn's internal structure. Also, occultation measurements provide important information on the planetary shape which is often not considered in structure models. In this paper we explore how wind velocities and internal rotation affect the planetary shape and the constraints on Saturn's interior. We show that within the geodetic approach (Lindal et al., 1985, ApJ, 90, 1136) the derived physical shape is insensitive to the assumed deep rotation. Saturn's re-derived equatorial and polar radii at 100 mbar are found to be 54,445 10 km and 60,365 10 km, respectively. To determine Saturn's interior we use {1 D} three-layer hydrostatic structure models, and present two approaches to include the constraints on the shape. These approaches, however, result in only small differences in Saturn's derived composition. The uncertainty in Saturn's rotation period is more significant: with Voyager's 10h39mns period, the derived mass of heavy elements in the envelope is 0-7 Earth masses. With a rotation period of 10h32mns, this value becomes <4 Earth masses, below the minimum mass inferred from spectroscopic measurements. Saturn's core mass is found to depend strongly on the pressure at which helium phase separation occurs, and is estimated to be 5-20 Earth masses. Lower core masses are possible if the separation occurs deeper than 4 Mbars. We suggest that the analysis of Cassini's radio occultation measurements is crucial to test shape models and could lead to constraints on Saturn's rotation profile and departures from hydrostatic equilibrium.

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Saturn and its Largest Moon Reflect Their True Colours

Posing for portraits for NASA's Cassini spacecraft, Saturn and its largest moon, Titan, show spectacular colours in a quartet of images being released today. One image captures the changing hues of Saturn's northern and southern hemispheres as they pass from one season to the next.
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Saturn and its rings cast striking shadows on each other in this mosaic of images captured by NASA's Cassini spacecraft.

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Image by NASA/JPL/Space Science Institute

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Saturn's Giant Storm
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Cassini Chronicles Life of Saturn's Giant Storm



New images and animated movies from NASA's Cassini spacecraft chronicle the birth and evolution of the colossal storm that ravaged the northern face of Saturn for nearly a year.
These new full-colour mosaics and animations show the storm from its emergence as a tiny spot in a single image almost one year ago, on Dec. 5, 2010, through its subsequent growth into a storm so large it completely encircled the planet by late January 2011.

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Aurora from Saturn moon 'circuit'

Saturn enjoys a flickering "Northern Lights" phenomenon thanks to a flow of electrons to and from its moon Enceladus, researchers say.
A report in Nature suggests these aurora would be faint, and in the ultraviolet part of the light spectrum.
The find by the Cassini spacecraft is similar to the electrical "circuit" between Jupiter and three of its moons.

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Geyser moon puts its mark on Saturn

An electrical current is flowing from Saturn's moon Enceladus to the ringed planet, creating a glowing patch in the planet's atmosphere.
Ultraviolet images taken by the Cassini spacecraft revealed the patch, which is distinct from the planet's auroras. It lies near Saturn's north pole - exactly where electrons emitted by Enceladus would hit after being channelled along the planet's magnetic field lines, report Wayne Pryor of Central Arizona College in Coolidge and colleagues.

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Saturn Kilometric Radiation
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Cassini Finds Saturn Sends Mixed Signals

Recent data from NASA's Cassini spacecraft show that the variation in radio waves controlled by the planet's rotation is different in the northern and southern hemispheres. Moreover, the northern and southern rotational variations also appear to change with the Saturnian seasons, and the hemispheres have actually swapped rates.
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Hot Plasma Explosions Inflate Saturn's Magnetic Field

A new analysis based on data from NASA's Cassini spacecraft finds a causal link between mysterious, periodic signals from Saturn's magnetic field and explosions of hot ionised gas, known as plasma, around the planet.
Scientists have found that enormous clouds of plasma periodically bloom around Saturn and move around the planet like an unbalanced load of laundry on spin cycle. The movement of this hot plasma produces a repeating signature "thump" in measurements of Saturn's rotating magnetic environment and helps to illustrate why scientists have had such a difficult time measuring the length of a day on Saturn.

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Cassini's CIRS Reveals Saturn Is on a Cosmic Dimmer Switch

Like a cosmic light bulb on a dimmer switch, Saturn emitted gradually less energy each year from 2005 to 2009, according to observations by NASAs Cassini spacecraft. But unlike an ordinary bulb, Saturn's southern hemisphere consistently emitted more energy than its northern one. On top of that, energy levels changed with the seasons and differed from the last time a spacecraft visited in the early 1980s. These never-before-seen trends came from an analysis of comprehensive data from the Composite Infrared Spectrometer (CIRS), an instrument built by NASA's Goddard Space Flight Centre in Greenbelt, Md., as well as a comparison with earlier data from NASA's Voyager spacecraft. When combined with information about the energy coming to Saturn from the sun, the results could help scientists understand the nature of Saturn's internal heat source.
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Hubble Captures Saturn's Double Light Show

In January and March 2009, astronomers using NASA's Hubble Space Telescope took advantage of a rare opportunity to record Saturn when its rings were edge-on, resulting in a unique movie featuring the nearly symmetrical light show at both of the giant planet's poles. It takes Saturn almost thirty years to orbit the Sun, with the opportunity to image both of its poles occurring only twice during that time. The 2009 Hubble Advanced Camera for Surveys data used in this movie have allowed astronomers to monitor the behaviour of Saturn's poles in the same shot over a sustained period of time and to analyse the planet's northern and southern lights simultaneously.
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