Nine Moments from the Cassini Mission that Shaped the Journey

Jupiter Flyby: I remember seeing our first image of Jupiter as we approached in late 2000 for our Jupiter flyby. We were so far away—about ½  the distance between the Earth and the Sun—and yet the detail was outstanding. I knew then that we were in for a remarkable experience at Saturn.

Phoebe, Saturn’s outer moon: Just a few weeks before we entered Saturn orbit, we collected images from a close flyby of Phoebe. We couldn't believe the detail. That was really the moment it all began. Westepped onto the conveyor belt, and didn't rest for the next 13 years.

Titan, Saturn’s largest moon: When the Huygens Probe landed on Titan, we saw the first image of the “shoreline,” and that unmistakable drainage pattern inland of that shore, which was a clear sign that liquid was either flowing presently or had in the past. That was essentially what we went to Saturn to see, and there it was, staring us in the face. Then came the Huygens image from the surface, only a few minutes later. Landfall on a moon in the outer solar system! We had arrived, and the solar system seemed, at that moment, a much smaller place. It was like being in one universe one moment, and in quite another the next. 

Titan’s Lake: We called it Lake Ontario, and it is located in the southern polar region of Titan.  It was our very first sighting of a lake on Titan.  We couldn't tell for sure if it was filled with liquid hydrocarbons, but observations by other instruments helped us confirm it. We found even larger bodies—the size of seas—in the north, this time in tandem with other instruments. Titan is a world out of science fiction, where the look of the place is familiar, but the feel is not. 

Enceladus: Seeing the plume, and eventually the geysers that form the plume, erupting from the south pole of Enceladus [another Saturn moon] was a remarkable experience. Those images made me feel a kinship with the first explorers, whoever they were, who first sighted the geysering turmoil of the Yellowstone region in the western U.S. For a planetary explorer, it really doesn't get any better than that. 

The Equinox: At one point, the Sun's rays shone on the rings at such a shallow angle that vertical structures in the rings—structures we had never seen before—revealed their presence by their long shadows. Among them, we found mountainous waves of ring rubble extending a few miles high above the rings, above this sheet of ring debris, only 30-feet thick.  Wild!

The Storm: A Saturnian storm erupted in 2010—the kind that comes every 20 or 30 years—and we were so fortunate to be there to witness it. 

Iapetus: Seeing the crazy, piebald surface of Iapetus and figuring out why it looks the way it does was another thrill. Together with the instrument that measures thermal radiation, we solved this long-standing puzzle – hundreds of years old -- of how Iapetus became the solar system’s two-toned moon.

“The Day the Earth Smiled”: This image was my version of the “Voyager Pale Blue Dot”—Pale Blue Dot 2.0. My idea was to re-do the original Pale Blue Dot picture (the concept and execution of which I was involved in), only make it better. And this time I added the twist that we would invite the public to be a part of the picture by being present, outside, thinking about life on a pale blue dot, as Cassini fired away. It was a great success, it really moved people the world over, and of course the picture is impossibly lovely. It shows the back-illuminated rings and Saturn, with the Earth a lovely blue dot a billion miles in the distance.  I’ll be boasting about this image and its significance for the rest of my days.

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By Carolyn Porco (PhD ’83 Planetary Science; 2011 Caltech Distinguished Alumna, Cassini Imaging Team Leader)

Photo: Last Cassini Project Science Group Meeting - September 2017-Caltech