Figure 1
Vertical structures created by Saturn's small moon Daphnis cast long
shadows across the rings in this dramatic image taken as the planet
approaches its mid-August 2009 equinox.
Daphnis,8 kilometers(5 miles)across, occupies an inclined orbit within the
42-kilometer (26-mile) wide Keeler Gap in Saturn's outer A ring. Recent
analyses by imaging scientists published in the Astronomical Journal
illustrate how the moon's gravitational pull perturbs the orbits of the
particles forming the gap's edge and sculpts the edge into waves that have
both horizontal and vertical components.
Measurements of the shadows in this and other images indicate that the
vertical structures range between one-half to 1.5 kilometers tall (about
one-third to one mile), making them as much as 150 times as high as the
ring is thick. The main A, B and C rings are only about 10 meters (about
30 feet) thick. Daphnis itself can be seen casting a shadow onto the
nearby ring.
In figure 1, a second version of the image that has been magnified to
twice its original size and cropped is also shown.
This image of shadows on the rings and others like it (see PIA11656 and PIA11655)
are only possible around the time of Saturn's equinox which occurs every
half-Saturn-year (equivalent to about 15 Earth years). The illumination
geometry that accompanies equinox lowers the sun's angle to the ringplane
and causes out-of-plane structures to cast long shadows across the rings.
This view looks toward the sunlit side of the rings from about 48 degrees
above the ringplane. The image was taken in visible light with the Cassini
spacecraft narrow-angle camera on June 8, 2009. The view was acquired at a
distance of approximately 666,000 kilometers (414,000 miles) from Daphnis
and at a Sun-Daphnis-spacecraft, or phase, angle of 130 degrees. Image
scale is 4 kilometers (about 2 miles) per pixel.
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 mission for NASA's Science Mission Directorate, Washington, D.C. The
Cassini orbiter and its two onboard cameras were designed, developed and
assembled at JPL. The imaging operations center is based at the Space
Science Institute in Boulder, Colo.
For more information about the Cassini-Huygens mission visit
http://saturn.jpl.nasa.gov/. The Cassini imaging team
homepage is at http://ciclops.org.
