Bill DunfordMar 24, 2014

Dancing With Saturn

As I type this, the robotic spacecraft Cassini is traveling at 2.4 kilometers per second (about 5,300 MPH) relative to the planet Saturn. On April 9th, when Cassini makes its closest approach to the planet during this current orbit, the craft will reach nearly 9 kilometers per second (about 20,000 MPH). For all that amazing speed, the pictures we see from Cassini are usually still shots, arrestingly beautiful--but also arrested in time.

Fortunately, we can get a sense of Cassini's intricate ongoing dance with Saturn and its moons, thanks to sequences of still images strung together into simple animations. Sometimes these sequences are just a series of routine observations; sometimes they are planned with moving images in mind. This magic is possible thanks to the Cassini engineering and science teams, who coordinate to build a list of painstakingly precise instructions, which they radio across a billion kilometers of space to the Saturn system. Cassini does the rest, spinning and pirouetting to orient its cameras just so, even as it careens at high speed past rings and icy moons.

The results are often striking. Here are a few of my favorites. I've applied very little post-processing to these sequences, but what they lack in polish compared to Hollywood CGI, they make up in being real.

Surging Sunlight
Surging Sunlight The bright glint of an opposition surge seems to follow Cassini as it observes Saturn's rings over the course of a couple of hours with the sun directly behind the spacecraft.Image: NASA / JPL-Caltech / SSI / Bill Dunford
Purple Haze in Motion
Purple Haze in Motion As Cassini neared Saturn's moon Titan for a close pass, layers of haze in the giant moon's atmosphere revealed themselves. (The color in these images is added.)Image: NASA / JPL-Caltech / SSI / Bill Dunford
Ice Shepherd
Ice Shepherd Cassini caught the shepherd moon Prometheus at work herding the icy particles of Saturn's F ring with its gentle gravitational field.Image: NASA / JPL / SSI / Animation by Bill Dunford
Buzzing Dione
Buzzing Dione Cassini captured this series of images as it flew near the ice world Dione in 2005.Image: NASA / JPL / SSI / Animation by Bill Dunford
Epimetheus and Family
Epimetheus and Family Epimetheus, as tracked by Cassini over the course of almost an hour as the moonlet orbited in the ring plane, along with other members of Saturn's family of worlds.Image: NASA / JPL / SSI / Animation by Bill Dunford
Spinning Saturn
Spinning Saturn Cassini watched over the span of about 90 minutes as Saturn turned on its axis, its atmosphere churned, and icy moons circled the scene.Image: NASA / JPL-Caltech / SSI / Bill Dunford
Enceladus Amid the Stars
Enceladus Amid the Stars Saturn's moon Enceladus, with its intriguing ice geysers, seems to be rocketing through space in this series of images taken by Cassini.Image: NASA / JPL-Caltech / SSI / Bill Dunford
Mimas and the Rings
Mimas and the Rings Cassini tracks Saturn's moon Mimas as it orbits near the rings. The sequence shown here took about 11 minutes to capture.Image: NASA / JPL-Caltech / SSI / Bill Dunford

And here's one more that was previously uploaded to the Saturn section of the Bruce Murray Space Image Library. I have to sneak it in, just because I think it happens to be one of the most amazing sights in the history of all exploration.

Saturn's north polar vortex (an animation)
Saturn's north polar vortex (an animation) Cassini took 14 images of Saturn's north polar vortex on 27 November 2012 over a period of many hours as the planet rotated beneath it. The 14 images have been processed to remove the geometric effects of Cassini's oblique viewpoint and of Saturn's rotation, holding the outer bright ring of white clouds fixed. With these motions removed, you can see individual vortices rotating and shearing, and the central clouds rotating faster than the outer ones.Image: NASA / JPL-Caltech / SSI / Kevin McAbee

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