Never-before-seen looming vertical structures, created by the tiny moon Daphnis, cast long shadows across the rings in this startling image taken as Saturn approaches its mid-August 2009 equinox.
Credit: CICLOPS/Cassini/NASA
SYDNEY: NASA's Cassini probe has uncovered for the first time towering vertical structures in Saturn's seemingly flat rings that are due to the gravitational effects of a small moon.
"We thought that this vertical structure was pretty neat when we first saw it in our simulations," said John Weiss, the paper's lead author at the Cassini Imaging Central Laboratory for Operations in the U.S. city of Boulder, Colorado. "But it's a million times cooler to have your theory supported by such gorgeous images. It makes you suspect you might be doing something right."
Surf's up
The new findings are detailed this month in The Astronomical Journal.
The search for ring material extending well above and below Saturn's ring plane has been a major goal during Cassini's Equinox Mission, the two-year period when the Sun is seen directly overhead at noon at the planet's equator.
This novel geometry – which occurs every half-Saturn-year – or about 15 Earth years, lowers the Sun's angle to the ring plane and causes "out-of-plane structures" to cast large shadows across the rings' broad expanse, making them easy to detect.
In recent weeks, Cassini's cameras have spotted not only the predictable shadows of some of Saturn's moons, but also the shadows of newly revealed vertical structures in the rings themselves.
Complex moon effects
These observations have lent dramatic support to the idea that small moons in very narrow gaps can have considerable and complex effects on the edges of their gaps, says the study, and that these moons can be smaller than previously believed.
The 8-kilometre-wide moon Daphnis orbits within the 42-kilometre-wide Keeler Gap in Saturn's outer A ring, and its gravitational pull perturbs the orbits of the particles forming the gap's edges.
The eccentricity (the elliptical deviation from a circular path) of the orbit of Daphnis can bring it very close to the gap edges, where its gravity affects the ring particles. Previous Cassini images have shown that as a consequence, the moon's effects can be time-variable and lead to the waves caused by Daphnis to change in shape with time and with distance from the moon.
