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Our Favorite Saturn Discoveries from Cassini 

Posted on Fri, September 15, 2017
  • by: Rebecca Ljungren, Astronomy Educator
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On September 15, NASA’s Cassini spacecraft plunged into Saturn, ending 13 years of exploration of the giant ringed planet and its system. The science conducted with Cassini data has been groundbreaking, and the spacecraft has gone where no spacecraft has gone before. Throughout Cassini’s nearly 20 year journey, many people around the world have had a chance to interact with the mission. Here at the National Air and Space Museum, we’re reflecting on what this mission has meant to us both professionally and personally. Priscilla Strain and Emily Martin of our Center for Earth and Planetary Studies as well as Genevieve de Messieres of our Astronomy Education Program weighed in on how Cassini has impacted them.

For researcher Emily Martin, learning about the mission was a “pretty surreal moment.” Martin explained:

“I was in college, and my professor walked into class with this article that had a picture of Saturn's moon Enceladus. There was this huge thing, a plume of water or snow, and it looked like it was just shooting out of the south pole of Enceladus! I just didn't think something like that was possible, so I convinced myself there must be some other explanation. But it only got better-- there was water shooting out of these big cracks called 'tiger stripes,' and it was getting flung around Saturn to create one of its rings.”

For Martin, images like the one of Enceladus helped define her career. “Cassini was in the throes of providing the community with some of the most spectacular images, revealing some really strange, alien places that I wanted to learn more about,” said Martin. “Of my 11 years studying icy moons, almost all of that time has been spent with Cassini images.”

A photo of Saturn's icy rings, taken by NASA's Cassini spacecraft on April 2, 2016.

Saturn’s bright, icy rings cross the field of view in this Cassini image, taken on April 2, 2016. The moon Dione is easily visible above the rings, but the smaller moon Epimetheus, just above the rings, is harder to spot. 

For Priscilla Strain, contact with the Cassini mission meant working with the people on the mission itself, such as Carolyn Porco. Porco is a planetary scientist that has worked on the Cassini mission for its entire history and is currently leading the imaging science team. Strain reminisced about having Porco here at the Museum:

“Ten years ago I invited Carolyn Porco, the Cassini imaging team leader, to give a talk for our Exploring Space Lecture Series. In her lecture titled ‘Expedition to the Ringed Planet: Cassini Explores Saturn, Its Rings, and the Fountains of Enceladus,’ she guided us through the discoveries seen over the first three years of Cassini at Saturn. I invited her back this year to speak on the mission and its legacy, and I was struck by the fact that through 10 more years Cassini had continued to consistently provide exciting new knowledge and results, a testament to both the mission design and the amazing diversity and complexity of the Saturn system. We discussed how Cassini is the mission that ‘just keeps on giving,’ even right up to the end with its daring dives between the rings and the planet.”

The vast treasure trove of data from Cassini, mined by those like Porco, Strain, and Martin, is an amazing resource and inspiration for those of us on Earth. Strain believes that some of the most exciting discoveries made by Cassini involve its moons. “Cassini opened our eyes to Titan’s hydrocarbon lakes and 'tasted’ the plumes spouting from Enceladus,” she shared. 

Martin agrees. Spectacular images of Saturn’s moons intrigued us all. One of Martin’s favorites involved an image of Enceladus, which showed two different kinds of terrains and a dark line running straight through it. 

“When you look at these kinds of images, you have to be aware of funny tricks cameras can play on your eyes, and ask yourself 'is this an artifact,is this real?,' said Martin. “The boundary between these two terrains was so dramatic, we actually wondered if it was some kind of artifact from the camera or some kind of trick our eyes were playing on us because of weird lighting. It turned out that this boundary was real, and I'm still scratching my head about how it got like that.”
 

A photo taken by NASA's Cassini spacecraft of the surface of Enceladus.

Cassini took this image of the surface of Enceladus on December 21, 2010.  At the upper right is new icy terrain, while the icy surface at lower left is older and cratered.

As an astronomy educator, Genevieve de Messieres looks at a lot of gorgeous and dramatic images from space. Some of her favorites are rainbow-colored nebulae, brilliant stars over national parks, and magnetic arches twisting above the Sun’s surface. So for her, it means something when she says that Cassini captured her favorite astronomy image. 

“Exactly 11 years ago, Cassini flew into the dark shadow of Saturn and turned its camera sunward, capturing a total solar eclipse. This image reveals a secret about the glorious rings. The tiniest particles of ice and dust are invisible from the sunny side of Saturn, but they light up when backlit. The Cassini team used this mosaic image, ‘In Saturn’s Shadow,’ to discover two new rings faintly glowing outside the main rings.”

But it’s a single, tiny detail that really gets her excited.

“My favorite secret from this magnificent image is a tiny detail, hardly more than a pixel. Just above and to the left of Saturn’s brilliant main rings is a faint spot of light. That dot is Cassini’s home world, the Earth, glimpsed from about a billion miles away. When I see it, I think of Carl Sagan’s words about another legendary picture of our Earth.”

A photo taken by Cassini while it was floating through Saturn's shadow.

This magnificent image of Saturn was created by combining multiple images taken over three hours on September 15, 2006, as Cassini floated through the darkness of Saturn’s shadow.  This image produced several scientific discoveries, including two previously unknown rings. Earth is the faint spot just to the upper left of Saturn’s main rings.

“There is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world. To me, it underscores our responsibility to deal more kindly with one another, and to preserve and cherish the pale blue dot, the only home we've ever known.”- Carl Sagan

Now that Cassini has made its final plunge into Saturn, will there be future missions like it? Martin believes there will be. “NASA has begun to establish an Ocean Worlds program, and has started thinking more about what we need to be able to continue exploring the outer solar system,” said Martin. “NASA has also been working on returning to Jupiter's moon Europa to explore its subsurface, salty ocean, and this is going to be the next big exciting mission to the outer solar system.” There seems to be a bright future ahead for outer solar system exploration, especially in the Saturn system. 

As we look toward the future, Martin hopes that we will still remember what was so impactful about the Cassini mission. 

“Cassini was an effort lead by teams from all over the world designing instruments and doing really amazing science,” said Martin. “I hope everyone remembers that science is important, exciting, and creative, and needs lots of different kinds of people to keep exploring and learning everything we can about our place in space.”

Thank you to Priscilla Strain, Emily Martin, and Genevieve de Messieres for their contributions to this story. All interviews edited for clarity and concision. 

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