* Astronomy

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Saturn's Rotation

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A new way of detecting how fast large gaseous planets are rotating suggests Saturn's day lasts 10 hours, 34 minutes and 13 seconds - over five minutes shorter than previous estimates that were based on the planet's magnetic fields.
The research, published in the journal Nature on July 30, was carried out by an international team led by scientists from Oxford University and the University of Louisville (USA).
Measuring the rotation of gas giants such as Saturn is difficult because the planet has no solid surface to use as a reference. Also, unlike Jupiter, Saturn's magnetic fields are aligned with its rotation axis so that their fluctuations do not give an accurate measure of the rotation of the planet's deep interior.
The new approach comes out of work begun over ten years ago by Timothy Dowling of the University of Louisville into measuring the movements of ammonia clouds across Saturn's surface and the work of Professor Peter Read of Oxford University, who has been using data from the NASA Cassini spacecraft's infrared spectrometer to study the planet's atmosphere since 2004.

Oxford University

-- Edited by Blobrana on Thursday 30th of July 2009 04:27:27 PM

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Saturn

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Never-before-seen Images From Saturn Kick Off Celebrations at Royal Observatory Greenwich in London
In anticipation of the upcoming equinox at Saturn, the imaging science team on NASA's Cassini spacecraft is releasing today a series of images and movies capturing scenes possible only once every 15 years.
This bounty of sights, that includes time-lapse sequences in which Saturnian moons eclipse each other and cast long shadows onto the planet's famous rings, represents only some of the fruits expected for the extended "Equinox Mission" for Cassini, the robotic explorer that has been orbiting Saturn since July 1, 2004.

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Fascinating images taken from Nasa's Cassini spacecraft reveal the ringed planet, its moons and rings in the most incredible detail yet.
Extraordinary glimpses of the planet's atmosphere and surfaces add to our expanding understanding of Saturn, as Nasa's Cassini Equinox mission approaches its second year.
The images show the incredible differences within the Saturn system. In one image, serene-looking rings are elegantly stacked up around Saturn's equator, making a striking contrast to the cratered appearance of its plethora of moons.
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Water maser emission from the Saturnian system
The presence of water has long been seen as a key condition for life in planetary environments. Prompted by recent discovery by the NASA's Cassini spacecraft of a water vapour "plume" emanating from Enceladus, one of the Saturnian satellites, radio astronomers wondered how abundant water is in the system of Saturn. The so-called maser emission of water molecules offers the most sensitive and robust way of detecting water vapour at radio wavelengths. This emission is unmistakably recognisable via its spectral feature at the wavelength of 1.35 cm. The discovery of the water maser emission coming from the clouds of water vapour in the Saturnian system is published in this week's issue of Astronomy and Astrophysics (Pogrebenko et al. 2009, Astronomy and Astrophysics, v. 494-2).
An international team of radio astronomers led by Dr. Sergei Pogrebenko of the Joint Institute for VLBI in Europe (JIVE, Dwingeloo, The Netherlands) observed the system of Saturn with radio telescopes in Medicina (INAF-IRA, Italy) and Metsähovi (TKK-MRO, Finland) for several hundred hours hunting for the elusive spectral signature of the water maser spectral line. Their determination was rewarded: several areas associated with various bodies of the Saturn system demonstrated statistically significant indications of water vapour maser emission.

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Title: On the recently determined anomalous perihelion precession of Saturn
Authors: Lorenzo Iorio
(Version 4)

The astronomer E.V. Pitjeva, by analysing with the EPM2008 ephemerides a large number of planetary observations including also two years (2004-2006) of normal points from the Cassini spacecraft, phenomenologically estimated a statistically significant non-zero correction to the usual Newtonian/Einsteinian secular precession of the longitude of the perihelion of Saturn, i.e. \Delta\pi_Sat = -0.006 ±0.002 arcsec/cy; the formal, statistical error is 0.0007 arcsec/cy. It can be explained neither by any of the standard classical and general relativistic dynamical effects mismodelled/unmodelled in the force models of the EPM2008 ephemerides nor by several exotic modifications of gravity recently put forth to accommodate certain cosmological/astrophysical observations without resorting to dark energy/dark matter. Both independent analyses by other teams of astronomers and further processing of larger data sets from Cassini will be helpful in clarifying the nature and the true existence of the anomalous precession of the perihelion of Saturn.

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Cassini Finds Mysterious New Aurora on Saturn
Saturn has its own unique brand of aurora that lights up the polar cap, unlike any other planetary aurora known in our solar system. This odd aurora revealed itself to one of the infrared instruments on NASA's Cassini spacecraft.

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Title: Saturn Forms by Core Accretion in 3.4 Myr
Authors: Sarah E. Dodson-Robinson (1), Peter Bodenheimer (2), Gregory Laughlin (2), Karen Willacy (3), Neal J. Turner (3), C. A. Beichman (1) ((1) NASA Exoplanet Science Institute, (2) UCO/Lick Observatory, (3) JPL)

We present two new in situ core accretion simulations of Saturn with planet formation timescales of 3.37 Myr (model S0) and 3.48 Myr (model S1), consistent with observed protostellar disk lifetimes. In model S0, we assume rapid grain settling reduces opacity due to grains from full interstellar values (Podolak 2003). In model S1, we do not invoke grain settling, instead assigning full interstellar opacities to grains in the envelope. Surprisingly, the two models produce nearly identical formation timescales and core/atmosphere mass ratios. We therefore observe a new manifestation of core accretion theory: at large heliocentric distances, the solid core growth rate (limited by Keplerian orbital velocity) controls the planet formation timescale. We argue that this paradigm should apply to Uranus and Neptune as well.

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Observations from NASAs Cassini spacecraft have been used to build, for the first time, a 3-D picture of the sources of intense radio emissions in Saturns magnetic field, known as the Saturn Kilometric Radiation (SKR).
The results will be presented by Dr Baptiste Cecconi, of LESIA, Observatoire de Paris, at the European Planetary Science Congress on Tuesday 23rd September.
The SKR radio emissions are generated by high-energy electrons spiralling around magnetic field lines threaded through Saturns auroras. Previous Cassini observations have shown that the SKR is closely correlated with the intensity of Saturns UV aurora and the pressure of the solar wind.
The measurements were made using Cassinis Radio and Plasma Wave Science (RPWS) experiment.

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