Saturn's bulging core implies moons younger than thought December 7, 2016 by Blaine Friedlander Please Register or Log in to view the hidden image! Saturn's moon Dione, foreground, appears darker than the moon Tethys because it has a lower surface albedo, as shown in a photograph taken from the Cassini spacecraft on March 23, 2010. At the time, Cassini was about 746,000 miles from Dione and about 1.1 million miles from Tethys. Credit: NASA/Jet Propulsion Lab Freshly harvested data from NASA's Cassini mission reveals that Saturn's bulging core and twisting gravitational forces offer clues to the ages of the planet's moons. Astronomers now believe that the ringed planet's moons are younger than previously thought. "All of these Cassini mission measurements are changing our view of the Saturnian system, as it turns our old theories upside down. It takes one good spacecraft to tell us how wrong we were in the past," said Radwan Tajeddine, Cornell research associate in astronomy and a member of the European-based Encelade (pronounced en-CELL-ad) scientific team that pored over the Cassini data and published a paper in the astronomy journal Icarus (January 2017). The Encelade team – lead by Valéry Lainey of the Paris Observatory – provided two key measurements in the research, "New Constraints on Saturn's Interior From Cassini Astrometric Data." The scientists measured Saturn's Love number (the rigidity of a planet) for the first time and confirmed Saturnian moons move away from the planet at a faster rate than expected. (Most moons, including Earth's moon, move away from their parent planet.) Read more at: http://phys.org/news/2016-12-saturn-bulging-core-implies-moons.html#jCp
http://www.sciencedirect.com/science/article/pii/S0019103516304183 New constraints on Saturn's interior from Cassini astrometric data Abstract Using astrometric observations spanning more than a century and including a large set of Cassini data, we determine Saturn's tidal parameters through their current effects on the orbits of the eight main and four coorbital Moons. We have used the latter to make the first determination of Saturn's Love number from observations, k2=0.390 ± 0.024, a value larger than the commonly used theoretical value of 0.341 (Gavrilov & Zharkov, 1977), but compatible with more recent models (Helled & Guillot, 2013) for which the static k2ranges from 0.355 to 0.382. Depending on the assumed spin for Saturn's interior, the new constraint can lead to a significant reduction in the number of potential models, offering great opportunities to probe the planet's interior. In addition, significant tidal dissipation within Saturn is confirmed (Lainey et al., 2012) corresponding to a high present-day tidal ratio k2/Q=(1.59 ± 0.74) × 10−4 and implying fast orbital expansions of the Moons. This high dissipation, with no obvious variations for tidal frequencies corresponding to those of Enceladus and Dione, may be explained by viscous friction in a solid core, implying a core viscosity typically ranging between 1014 and 1016 Pa.s (Remus et al., 2012). However, a dissipation increase by one order of magnitude at Rhea's frequency could suggest the existence of an additional, frequency-dependent, dissipation process, possibly from turbulent friction acting on tidal waves in the fluid envelope of Saturn (Ogilvie & Lin, 2004; Fuller et al. 2016).
More Saturnian News: http://phys.org/news/2016-12-cassini-transmits-images-orbit.html Cassini transmits first images from new orbit December 7, 2016 Please Register or Log in to view the hidden image! This view from NASA's Cassini spacecraft was obtained about half a day before its first close pass by the outer edges of Saturn's main rings during its penultimate mission phase. Credit: NASA/JPL-Caltech/Space Science Institute NASA's Cassini spacecraft has sent to Earth its first views of Saturn's atmosphere since beginning the latest phase of its mission. The new images show scenes from high above Saturn's northern hemisphere, including the planet's intriguing hexagon-shaped jet stream. Cassini began its new mission phase, called its Ring-Grazing Orbits, on Nov. 30. Each of these weeklong orbits—20 in all—carries the spacecraft high above Saturn's northern hemisphere before sending it skimming past the outer edges of the planet's main rings. Cassini's imaging cameras acquired these latest views on Dec. 2 and 3, about two days before the first ring-grazing approach to the planet. Future passes will include images from near closest approach, including some of the closest-ever views of the outer rings and small moons that orbit there. Read more at: http://phys.org/news/2016-12-cassini-transmits-images-orbit.html#jCp
https://saturn.jpl.nasa.gov/news/2966/ring-grazing-orbits/ Cassini makes first ring-grazing plunge December 6, 2016 Please Register or Log in to view the hidden image! This graphic shows the closest approaches of Cassini's final two orbital phases. Ring-grazing orbits are shown in gray (at left); Grand Finale orbits are shown in blue. The orange line shows the spacecraft's Sept. 2017 final plunge into Saturn. Credit: NASA/JPL-Caltech NASA's Saturn-orbiting Cassini spacecraft has made its first close dive past the outer edges of Saturn's rings since beginning its penultimate mission phase on Nov. 30. Read more at: http://phys.org/news/2016-12-cassini-ring-grazing-plunge.html#jCp
