Charged Up Saturn

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Saturn’s translucent ring detail. Click for larger view. Saturn is the only planet less dense than water (about 30 percent less). In the unlikely event that a large enough ocean could be found, Saturn would float in it.
Credit: NASA/JPL

Although Cassini has only been orbiting the planet Saturn since July 1, data from the Cassini Plasma Spectrometer (CAPS) has already begun to provide new information about the curious nature of Saturn’s space environment.

CAPS had been detecting advance readings for several days before Cassini finally crossed the bow shock that exists in the solar wind ahead of the magnetosphere, a huge magnetic field bubble produced in the solar wind by Saturn’s strong magnetic field. On June 28, the spacecraft entered into the magnetosphere itself and began taking data. From this very preliminary set of measurements, it is apparent that the outer reaches of Saturn’s magnetosphere are probably populated by plasma captured from the solar wind, but closer to the planet the plasma comes primarily from the rings and/or the inner icy satellites.

According to Michelle Thomsen, the current Los Alamos CAPS project leader, "After many years of design, development and testing, and then the seven-year journey across the solar system, CAPS is finally doing the job it was built to do. We are quickly learning much, but I think we have only begun to understand what CAPS can teach us about Saturn and its space environment over the next few years."

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Saturn rings in shadow. Image Credit: NASA/JPL

CAPS consists of three separate analyzers designed to measure the electrically charged particles trapped within Saturn’s magnetosphere. Los Alamos played a major role in the design and construction of two of them: an ion mass spectrometer (IMS), which incorporates a novel design developed at Los Alamos to identify the different atomic species in Saturn’s magnetospheric plasma, and an ion beam spectrometer (IBS), which is based on a design used by Los Alamos scientists on several previous solar wind research missions.

During Cassini’s first brief pass over Saturn’s rings, CAPS identified a previously unknown low-energy plasma trapped on the magnetic field lines threading the Cassini Division, the name given to the gap between the main A and B rings.

Around 1655, the Dutch scientist, Huygens first recognized that Saturn was "girdled by a thin, flat ring, nowhere touching it." The lettering scheme, "A through F", refers to the historical order of the ring divisions’ discoveries, and does not relate easily to their distance from Saturn. Gaps in the rings are caused by a resonant gravity connection between the thirty-plus moons and the dust halo that surrounds Saturn. Saturn itself has often been compared to a mini-solar-system, since most dust aggregation models for planets and stars involve similar disks with orbital sweeping. The other gas giants like Jupiter and Uranus also have rings but much fainter than the signature characteristic of the sixth planet from the Sun.

With the four-year mission just beginning, including more than 70 orbits of the planet, CAPS is poised to provide scientists with a new level of understanding about Saturn’s space environment, as well as clues about some of the space physics processes that operate more universally in the solar system.


Related Web Pages

Cassini
Saturn Edition, Astrobiology Magaz.
Saturn’s Rings in UV
Cassini Closes In on Saturn

Saturn– JPL Cassini Main Page
Lord of the Rings
Space Science Institute, Imaging Team Boulder, Colorado
Saturn: The Closest Pass