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Accueil > A propos du LPP > Communication > Actualités archivées > 2020 > The charged dust at Saturn is making its equatorial ionosphere much more conductive !

The charged dust at Saturn is making its equatorial ionosphere much more conductive !

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A new study led by scientists at Imperial College London and the Laboratory of Plasma Physics (LPP) and recently published in Nature Scientific Reports (freely available in open access) presents the first in-situ estimates of Saturn’s ionospheric conductivity, highlighting the key role played by the charged dust.

Saturn and its icy rings are some of the most dazzling and unique objects in our solar system. Both, the gas giant and its rings have their own ionospheres that are connected to each other via Saturn’s magnetic field. An ionosphere is formed by sunlight ionizing part of the atmosphere into positive ions and electrons. Because of the charged particles, this layer becomes electrically conductive and may carry electrical currents. Such currents carry energy, and as they flow out of (or into) the ionosphere on the “wires” – magnetic field lines, they connect together Saturn’s ionosphere and rings.

Vue de Saturne et de ses anneaux prise par Cassini

Prior to the final phase of the Cassini’s spacecraft mission known as “the Grand Finale” no direct measurements of Saturn’s ionosphere were done and its properties were only based from the remote measurements (by Pioneer 11, Voyagers 1&2 and Cassini) and the associated numerical models.

On April 2017, Cassini started its Grand Finale final phase executing a series of 23 orbits passing between Saturn and its rings every week before it plunged into the gas giant’s atmosphere on the fateful 15th of September 2017, ending its 13-year mission. The plasma, particle and magnetic field instruments onboard the Cassini spacecraft brought the first ever direct (in-situ) observations of Saturn’s upper atmosphere. In particular, the dust of the innermost rings was discovered to fall into Saturn’s atmosphere under the gas giant’s gravity and atmospheric drag. Upon entering the ionosphere, the dust grains absorb the electrons, almost completely depleting their numbers and forming a layer around the ring plane (equator) with enhanced ion densities. This enhancement, along with the introduction of the charged dust, plays an important role in the interaction between Saturn’s ionosphere and magnetosphere.

In the article Shebanits, Hadid, et al., Sci. Rep., 2020, the authors use simultaneous measurements from the plasma, particle and magnetic field instruments on-board the Cassini spacecraft : the Langmuir probe (part of the Radio and Plasma Waves Science package), the Ion and Neutral Mass Spectrometer and the Cassini Magnetometer. They show that the electrically conductive region of Saturn’s equatorial ionosphere is at least twice as thick and with conductivities and at least 10-100 times higher than previously estimated. The cause is dust grains, sourced by the previously discovered “ring rain” – falling in from the innermost rings.
The results of this new study highlight the important role of the charged dust and will improve existing models of Saturn’s atmosphere and its coupling to the rings by the planet’s magnetic field.

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