The Cassini Orbiter’s greatest images and discoveries

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The Cassini Orbiter’s greatest images and discoveries

The Cassini-Huygens mission launched from Cape Canaveral on October 15, 1997, and last week, just a month shy of 20 years later, one of the most prolific purveyors of beautiful planetary science crashed into Saturn in a bittersweet “Grand Finale.” With its fuel nearly exhausted, this is its final and most dramatic experiment.

The first eight of those years were spent looping around the inner planets to build up speed, but once it arrived at its destination, the science came fast and furious. Every one of its 12 subsequent years around Saturn produced stunning imagery and fascinating data about our solar system’s most photogenic planet. As a celebration of Cassini’s final day, here are some of its most striking images and unexpected discoveries.

We’ll start with its launch and journey to Saturn, then see how Cassini offered new views on the planet’s rings, surface and many many moons — and then the craft’s final descent.

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Cassini and Huygens

Cassini is the star today, but Cassini-Huygens was a combo mission between NASA and the European Space Agency. While Cassini would orbit Saturn for years, the Huygens probe, which we can spare a slide for later, was aimed at the moon Titan, a fascinating moon covered in liquid hydrocarbons.

Both launched as a single package on October 15, 1997 aboard a Titan IVB/Centaur rocket.

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Flyby of Jupiter

Although Cassini’s main mission was to investigate Saturn and its moons, the team couldn’t pass up the opportunity to swing by Jupiter on the way. It would also give the team a chance to check the spaceworthiness of the craft’s scientific instruments ahead of their true test.

As part of this side mission, Cassini produced this incredible photo of Io, dwarfed against the gas giant’s swirling surface.

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Maps of Jupiter's poles

During its 2000 flyby of Jupiter, Cassini managed to produce the best imagery of Jupiter that would be taken until Juno arrived many years later. This psychedelic map of Jupiter’s south pole (you can see the red spot in the northwest quadrant there) was a revelation. The corresponding north pole map is here.

New investigations of the planet’s magnetosphere and aurora were also undertaken, but it wasn’t until Juno that we would crack some of those secrets.

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Saturn's rings in glory

Cassini’s powerful instruments captured this iconic view of the many-ringed planet while it was backlit by the sun. Apart from being astonishingly beautiful, this shot and others like it helped scientists identify entirely new rings illuminated by the slanting light.

Other interesting phenomena in the rings were observed as well…

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"Spokes" in the rings

We’ve known for years that there were irregularities in the rings, but Cassini’s regular observations showed them in unprecedented detail. These formations spinning around the rings are known as “spokes,” and are actually ice clouds the size of Asia.

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Fine details

In Cassini’s closest images of the rings, they are revealed to have structure finer than its instruments can discern. Here, in the B-ring, are hundreds of tiny waves, which are actually the same trace of material wrapped around Saturn in a spiral, then raised up by the close passage of the moon Janus.

Saturn’s rings may be among the most striking sights in the system, but they’re also some of the most complex things we have encountered, rife with history and unexpected effects. We may never know the whole story, but Cassini has helped fill in the gaps quite a bit.

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Delicate, shifting colors on Saturn's surface

The improved optical qualities of Cassini’s cameras means views of Saturn that truly reflect what we would see could we join it in its orbit. This natural-color image shows the painterly spreads of gold, beige, pink and a lovely blue at the north pole.

Those colors aren’t just for show: each indicates where different compositions of gases have bubbled to the surface, due to atmospheric trends or enormous storms.

And then there’s the most intriguing storm of all…

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Behold the hexagon

Surely the most bizarre and fascinating surface feature of Saturn, the hexagon. This shape is the result of six jet streams producing the familiar shape and occasionally forming 2,000-mile-wide Saturnian hurricanes.

The colors you see here are from 2013 (left) and 2017 (right); we’re not quite sure why the color changed so much, except that it’s likely caused by increased sun exposure on the area. Does that change the composition of the haze we see? Does it whip up new storms that churn new colors up from the bottom? Does it reflect a larger seasonal change? Scientists have many hypotheses.

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9/19

Fluid dynamics in action

Saturn’s “surface” is really just the outer layer of an enormous ball of mixed gases. As such, Cassini’s close-ups provide a great opportunity to see how bodies such as this one behave. The lovely swirls visible at any given time and constantly changing are suitable for framing, but also make for interesting study by scientists curious about the many, many factors that go into an enormous, turbulent planet’s fluid dynamics.

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Pulling back the veil from the mysterious Titan

Saturn’s largest moon Titan is covered in a thick layer of haze — but Cassini’s instruments, tailor-made for this purpose, peered right through it to find a world that defied scientists’ predictions. Instead of a vast ocean of liquid hydrocarbons, the surface is dotted with lakes and rivers, surprisingly Earth-like (except that it’s all horribly toxic and freezing cold).

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Monster lakes

Titan’s lakes, once seen clearly, received wonderfully evil-sounding names. There’s Ligeia, after Poe’s doomed heroine; Punga, after a mythological sea creature; and you know the Kraken.

The complex surface of Titan has been catnip for planetologists, who eagerly dissected each new piece of imagery for hints at the moon’s history and composition.

Good thing we brought along Huygens…

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Huygens descends

In a brief but glorious mission, the Huygens lander descended through Titan’s hazy atmosphere, sending back incredible readings and imagery for over three hours until it succumbed to the moon’s harsh environment.

Huygens did in fact touch down and sent back an image from the surface before conking out. It holds the record for the farthest spacecraft landing from Earth.

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13/19

Enceladus, prime candidate for life

At first glance an ice-covered moon of Saturn doesn’t strike one as a great prospect for life. But when you consider the extreme conditions of many a body in the solar system, Enceladus starts to look downright hospitable.

Beneath an admittedly hostile shell is what appears to be an enormous lake of liquid water — which means temperatures and pressures that are known to support life. Add methane to the mix and you’ve got a source of energy, as well. There’s no reason why our own extremophile organisms couldn’t survive there with a little adaptation — but perhaps it’s already inhabited.

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Gotta jet!

The famous plumes of Enceladus were observed decades ago, but a more detailed survey found that the moon is covered in them. These “tiger stripes” near the south pole are among the most prominent.

Observing and “tasting” these plumes allowed scientists to infer the makeup and internal activity of the moon. There were 20 times the amount of organic materials expected, making Enceladus an exciting prospect for extraterrestrial life.

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That's no moon! Wait, yes it is

Among Saturns 53 moons are found all manner of shapes and origins, and the amazing imagery sent back by Cassini has revealed something new about just about all of them (especially those it discovered).

Mimas, for instance, sports a crater and overall surface that’s uncannily like the Death Star…

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Light side and Dark side

And in a living embodiment of the Force, Iapetus has a dramatic half-and-half setup where one side of the moon is stark white and the other coal black. This was found be because the moon, like our own, is tidally locked with Saturn and always faces it — meaning dust from the disintegrating Phoebe falls only on the other, coloring it.

Honestly there is just way too much about the moons to go over here. You can see each one individually at this helpful catalog over at NASA.

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17/19

"The day the Earth Smiled"

Like the Pale Blue Dot taken by Voyager, this incredible image is at once breathtaking and humbling. The rare opportunity to catch Earth in the background of a stunningly back-lit Saturn and its colorful rings was too good to pass up.

In this shot, Earth is 898 million miles away, and if you look really closely, the moon is sort of attached on its right.

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The final plunge

After making its final orbit, Cassini entered the atmosphere of Saturn at over 77,000 miles per hour, using the last of its energy to keep its antenna pointed at the Earth, sending data back until the very last second.

It may seem cruel to send a venerable spacecraft to certain doom, but the truth is this is Cassini’s ultimate purpose and was always the plan. One last experiment, to make history one last time.

Here, in one of the final sets of images sent back by the probe, we see Enceladus setting behind Saturn itself as Cassini began its descent.

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Mission complete

It was an emotional moment at mission control as Cassini’s signal winked out forever. Earl Maize and Julie Webster, Program manager and spacecraft operations team manager for the mission respectively, share a hug after the craft’s final plunge.

We salute Cassini, Huygens and the international team of engineers and scientists who made possible this incredible mission!

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