Thursday, December 13, 2007

Cassini Captures Best View Yet Of Saturn’s Ring Currents

Credit: (All Images)
NASA/Jet Propulsion Laboratory/
Johns Hopkins University Applied Physics Laboratory (NASA/JPL/JHUAPL)

Particle Population in Saturn's Magnetosphere

This is an artist’s concept of the Saturnian plasma sheet based on data from the Cassini Magnetospheric Imaging Instrument. It shows Saturn's embedded “ring current,” an invisible ring of energetic ions trapped in the planet’s magnetic field.

Saturn is at the center, with the red “donut” representing the distribution of dense neutral gas outside Saturn's icy rings. Beyond this region, energetic ions populate the plasma sheet to the dayside magnetopause filling the faintly sketched magnetic flux tubes to higher latitudes and contributing to the ring current. The plasma sheet thins gradually toward the nightside. The view is from above Saturn’s equatorial plane, which is represented by grid lines. The moon Titan’s location is shown for scale. The location of the bow shock is marked, as is the flow of the deflected solar wind in the magnetosheath.

Saturn's ‘Ring Current’

Like Earth, Saturn has an invisible ring of energetic ions trapped in its magnetic field. This feature is known as a “ring current.” This ring current has been imaged with a special, APL-designed camera on Cassini sensitive to energetic neutral atoms.

This is a false color map of the intensity of the energetic neutral atoms emitted from the ring current through a processed called charge exchange. In this process a trapped energetic ion steals and electron from cold gas atoms and becomes neutral and escapes the magnetic field.

The Cassini Magnetospheric Imaging Instrument’s ion and neutral camera records the intensity of the escaping particles, which provides a map of the ring current. In this image, the colors represent the intensity of the neutral emission, which is a reflection of the trapped ions. This “ring” is much farther from Saturn (roughly five times farther) then Saturn’s famous icy rings. Red in the image represents the higher intensity of the particles, while blue is less intense.

Saturn's ring current had not been mapped before on a global scale, only "snippets" or areas were mapped previously but not in this detail. This instrument allows scientists to produce movies that show how this ring changes over time. These movies reveal a dynamic system, which is usually not as uniform as depicted in this image. The ring current is doughnut shaped but in some instances appears as if someone took a bite out of it.

This image was obtained on March 19, 2007, at a latitude of about 54.5 degrees and radial distance of 1.5 million kilometers (920,000 miles). Saturn is at the center, and the dotted circles represent the orbits of the moons Rhea and Titan. The Z axis points parallel to Saturn’s spin axis, the X axis points roughly sunward in the sun–spin axis plane, and the Y axis completes the system, pointing roughly toward dusk. The ion and neutral camera’s field of view is marked by the white line and accounts for the cutoff of the image on the left. The image is an average of the activity over a (roughly) 3-hour period.

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Magnetospheric Imaging Instrument was designed, built and is operated by an international team lead by the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.

‘Ring Current’ Rotation

This series of Magnetospheric Imaging Instrument images shows the energetic neutral atom emission from Saturn's ring current. The sun is to lower left (X axis), and the orbits of the moons Titan, Rhea and Dione, and Saturn’s rings, are shown. The pronounced asymmetry (bright emission in the upper quadrant, located between midnight and dawn) rotates with the planet, and the bright spot rotates through 360 degrees over one Saturn rotation (about 10 hours and 40 minutes).

The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Magnetospheric Imaging Instrument was designed, built and is operated by an international team lead by the Johns Hopkins University Applied Physics Laboratory, Laurel, Md. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL.