In anticipation of the upcoming equinox at Saturn, the imaging science team on NASA's Cassini spacecraft is releasing a series of images and movies capturing scenes possible only once every 15 years.
This bounty of sights, that includes time-lapse sequences in which Saturnian moons eclipse each other and cast long shadows onto the planet's famous rings, represents only some of the fruits expected for the extended "Equinox Mission" for Cassini, the robotic explorer that has been orbiting Saturn since July 1, 2004.
Saturn's spin axis is tilted relative to its motion around the sun, and its year is equal to 29.5 Earth years. Equinox, the twice-yearly period when the sun passes through the plane containing the planet's rings, will happen for the first time in almost 15 Earth years on Aug. 11, 2009.
The novel illumination geometry created by the approaching equinox lowers the sun's angle to the ring plane and causes some of Saturn's moons, as well as out-of-plane structures in the rings, to cast long shadows across the rings, creating vistas never before seen by any Saturn-bound spacecraft.
In fact, only recently, Cassini's high-resolution camera spotted for the first time, on the edges of a gap in Saturn's outer ring, enormous mile-high vertical waves whose presence was unknown until betrayed by the waves' shadows.
Speaking of the recent images of the rings acquired as Saturn marches towards its mid-August equinox, Carolyn Porco, leader of the Cassini Imaging Team, said:
"It has been a scientist's delight to watch this almost wafer-thin collection of icy debris, that we have come to know so well, change in character and spring into the third dimension. Five years into this mission and we find there are still new tales to be told." Porco is also the Director of the Cassini Imaging Central Laboratory for Operations in Boulder, Colorado.
The release of the new images coincides with the opening of a week-long celebration of the Cassini mission and all that it has discovered in the last 5 years. A unique exhibition of the mission's images revealing the beauty of Saturn, its rings and moons, opens at the Royal Observatory, Greenwich.
"Visions of Saturn" features striking pictures of hurricane-force storms in Saturn's turbulent atmosphere, the delicate tracery of the ring system and a weird and wonderful array of satellites, including Enceladus – the whitest place in the solar system – and a planet-sized moon where liquid methane rains from an orange sky.
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