The image on the left was taken on Nov. 1, 1980, by NASA's Voyager spacecraft from a distance of 5.3 million kilometers (3.3 million miles). It shows a very strong narrow shadow cast on the equatorial region of Saturn's atmosphere by the rings. During the Voyager encounters, the Sun was close to the plane of the rings so that the ring shadow was very deep and localized to low latitudes.
Radio signals detected by Voyager were interpreted as lightning coming from a persistent, extended storm system at low latitudes. It is possible that the ring shadow was partly responsible for generating this storm by promoting strong convection at the boundary of the colder shadowed atmosphere and the adjoining sunlit atmosphere. This image was previously released on June 19, 1999. For original caption see PIA00335.
The image on the right was acquired by the Cassini spacecraft on May 10, 2004, from a distance of 27.2 million kilometers (16.9 million miles) and shows the complex set of ring shadows cast over a large region of Saturn's northern hemisphere. This shadow pattern is due to the Sun being well below the ring plane during Cassini's approach to Saturn. This image was previously release on May 25, 2004. For original caption see PIA05394.
Unlike the situation when NASA's Voyager spacecraft flew by Saturn, these ring shadows are not as deep and are not localized at a very narrow range of latitudes. Should these shadows drive convection in Saturn's atmosphere, the location would likely be very much different than the near-equatorial shadow observed by the Voyagers in the early 1980s. It is possible that this very different ring shadow geometry is one reason for different morphologies of thunderstorms observed by Cassini and Voyager. Voyager observed lightning apparently from one persistent, low-latitude storm system, whereas Cassini observes lightning from storms which seem to come and go on time scales of a day or so, and perhaps from more than one storm system at a time.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington, D.C. The Cassini orbiter was designed, developed and assembled at JPL. The radio and plasma wave science team is based at the University of Iowa, Iowa City.
For more information about the Cassini-Huygens mission, visit http://saturn.jpl.nasa.gov and the instrument team's home page, http://www-pw.physics.uiowa.edu/plasma-wave/cassini/home.html .
NASA/JPL/University of Iowa