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The Cassini orbiter was launched on October 15, 1997, from Cape Canaveral Air Force Station in Florida, and along with the Huygens probe began a journey that would eventually last almost 20 years. Cassini’s Grand Finale-the moment when the exploratory mission backed by 27 nations sends its last data signal across the solar system-took place September 15, 2017, at which point Cassini was set adrift by NASA into Saturn’s upper atmosphere and burnt to a mechanical crisp. During the 13-plus years Cassini was studying Saturn its accomplishments and statistics were other-wordly impressive, including:
- 635 gigabytes of data collected.
- Over 450,000 images taken.
- 4.9 billion miles (7.8 billion kilometers) traveled since it was launched.
- 294 orbits of Saturn completed.
- Cost of the mission: $3.9 billion (U.S. dollars).
Since forever, humans have gazed skyward, wondering what’s up there in that big black forever universe. Thanks to ingenuity, brilliant scientists and engineers that can get incredible amounts of data from computers that are nearly outdated by the time they arrive at their destination, we have a much better sense of the stars and planets.
One of the greatest tools in the human stargazing and planetary arsenal was Cassini, a probe that hurtled toward Saturn in 1997 and spent the next 10 years traveling toward and studying the massive planet.
A joint project of NASA, the European Space Agency and the Italian Space Agency (ASI), Cassini was the first to land on a planet in the outer solar system (Titan, Saturn’s largest moon) and offered some insights onto how life started here at home. It took Cassini seven years to get to Saturn and another several months for the Huygens probe to land on Titan.
By the time Cassini threw itself into Saturn’s corrosive atmosphere in September 2017, it sent back enough information to fill a library’s worth of research books. (Source: ESA)
A few stats on Cassini first:
The mission cost $3.9 billion (including $2.5 billion to build and launch the vessel and another $1.4 for in-mission expenses); involved a crew of some 5,000 people; provided enough material for the publication of 3,984 research papers; traveled 1.2 billion miles; had a four-year primary mission that was extended twice to allow for more information to be gathered; took and sent back 453,048 images and collected 635 GB of data while executing 2.5 million commands. (Source: JPL)
Here’s a greatest hits list of Cassini’s discoveries, in no particular order:
1. Cassini discovered six named moons that no one knew existed or had mapped. The moons range in size from your typical sports arena (tiny!) to the size of Mercury (what!?) and feature some pretty interesting geological features, some of which will be addressed below. Some are spherical and look like our moon, others are really wonky and shaped like potatoes or irregular objects. Some have smooth surfaces, others are pocked and rocky. There’s even a moon that is in some state of being in one of Saturn’s rings – whether it’s being formed or being ripped apart, scientists aren’t sure. Thanks to Cassini, we know that Saturn has a whopping 60 moons, which has to set some kind of record. Up for the crown of coolest moon? Mimas, which kinda looks like the Death Star in Star Wars. (Source: JPL)
2. On Titan, one of Saturn’s moons, Cassini found three seas and hundreds of small lakes. On a moon! It’s oddly a lot like Earth, with liquid hydrocarbons and methane taking the place of water, but it might support a kind of life we’d never considered before. Earth is warmer, because it’s closer to the sun, but Titan is very much an Earth-like body with a similar atmosphere, even if that atmosphere is more than 370 miles (600 km) high. The air on Titan, so to speak, is made up of nitrogen and methane, which gives us another mystery: Sunlight breaks down methane, so where it is at all coming from? It might be a volcano, but we’re not sure yet and won’t be for quite some time. Oh, also? Titan has sand dunes like ones you’d see in Namibia. (Source: Jet Propulsion Lab, PopSci, Space.com)
3. On Enceladus, another moon, Cassini found water, actual water, underneath the icy terrain. It was instantly declared one of the most scientifically interesting destinations for research, given the seemingly improbable odds of finding water that far out on the fringes of the Milky Way. Oh, by the way? The water occasionally spurts out in jets, spraying water vapor and icy particles that likely contain a lot of salts. (Source: The Hindu)
4. The moon Iapetus would seemingly disappear at times, confusing astronomers. Come to find out, one side of the moon is pure white, while the other is darkest black. Much like our moon, Iapetus is locked with Saturn, meaning only one side is ever facing the planet. In what might seem paradoxical, the light side is always collecting ice and getting brighter, while the dark side heats up and ditches the ice. (Source: PopSci)
5. At least one mystery that remains unsolved: Cassini poked around and studied the giant storms on Saturn’s poles, determined they were hurricanes, and found unusual but completely natural radio waves from inside the planet, but no one knows (yet) where they come from, how they originated or what they’re doing. (Source: Telegraph)
6. While floating in the nothingness around Saturn, Cassini found itself caught in a terrifically strong wind. The particles in that wind were whizzing past at nearly the speed of light, a kind of acceleration that also happens in supernovas, but those are usually too far away to study in a meaningful and direct way. Scientists studied these patterns, particles and waves and determined that some kinds of shocks can be better particle accelerators than others, and in particular the quasi-parallel shocks, in which magnetic fields and the “forward” facing direction of the shock are just about lined up, are tremendously powerful. (Source: JPL)
7. There could be Fake Plastic Trees on Saturn. Well, ok, not really, but propylene, a core ingredient in plastics, was detected on the planet, the first place it’s been found other than on Earth. It’s a relatively simple molecule, a chain of three carbon molecules, and yet it’s vital to so much of what we consume and produce here and it’s largely a byproduct of oil refining and fossil fuel extraction. So what was it doing on Saturn? Scientists say it’s not too surprising, given its simplicity, but they had never found it there before. They used Cassini’s infrared spectrometer, a funky tool that reads atomic movement and compositions, to find it. But it’s not like there will be a need to farm out our supply of propylene for car bumpers or storage containers just yet, because it’s still abundant and cheap here. (Source: Wired)
8. Saturn’s best known for its rings, gravity-bound collections of rocks and ice and debris. But the rings are not static; they change and evolve as they are hit by meteoroids or other bits of debris. (There’s a good amount of debris of various origin in space.) As a result, the rings become a little wavy and rippled. What’s even more fascinating is that scientists studied a set of photos collected by Cassini in 2013 and, after their computations and research, they developed a model that could determine when the strikes happened, including a ripple from 1983 that stretched for 12,000 miles. (Source: Space)
9. It might be easy to take this for granted, but Cassini brought back our first clear images of the massive polar hurricane on Saturn and the odd hexagon there. Scientists say the storm is caused by fluid dynamic and a speedily rotating atmosphere, but it’s also the first storm of its kind found on a gas planet. It’s also really, really big: 20,000 miles or 32,000 kilometers wide and it extends for some 60 miles, or 100 km. It’s a big ol’ storm. The hexagon does not move from its latitude and has such a predictable location it can be recreated in computer simulations. (Source: Forbes)
10. It was mentioned earlier that Enceladus has liquid water, which is pretty incredible on its own. But now scientists are thinking there could be a form of life there as well. The Arizona-sized moon has an atmosphere containing mostly hydrogen and carbon dioxide as well as methane and researchers know there are certain microbes, like methanogenic archaeon, release methane as a byproduct (just like cows!). Researchers ran some tests and confirmed that those microbes could, in fact, survive in the conditions known to exist on Enceladus, even if the atmospheric pressure is 50 times greater than here on Earth, and they believe the best possible place to find them is on the floor of the moon’s seas. But we’ll have to go back to really explore. (Source: Forbes)
11. As Cassini was floating around Saturn, taking photos and dropping jaws, it was hit with a massive jolt of static electricity. Befuddled, scientists grabbed their readings and try to determine what might’ve caused the disruption. They believe the satellite received a 200 volt shock from Hyperion, another of Saturn’s moons, which also implies that Hyperion itself is conducive and reactive to electricity. A study published in 2014 suggests Cassini was magnetically connected to the surface of Hyperion, like a sock to a balloon, as electrons moved across the moon. This is really cool, but it also serves as a warning to future interplanetary explorers that the surface of planets could mess with their electronics and their safety gear as they try to conduct their research or set up a colony. (Source: UCL News)
12. Cassini didn’t want Saturn and its myriad moons to get all the attention, however. The little probe that could also took some of the most detailed and vivid photos we’ve ever seen of Jupiter, including the bright red, swirling storm that can be picked up on some amateur telescopes. The photos were stitched together, digitally, from a mosaic taken on December 29, 2000 at a distance of 6.2 million miles (10 million km) and shows features as small as 37 miles (60 km) wide. It allowed researchers to determine the fastest jet stream on Jupiter moves at about 300 miles per hour (480 km/h). The atmosphere on Jupiter is incredibly turbulent, as evidenced by the Great Red Spot’s longevity and that all we see of Jupiter is cloud cover. (Source: NASA)
13. During its final days, Cassini didn’t look to retire gracefully or quietly. Instead, it conducted a series of dives into and through Saturn’s rings to study their content and the planet’s atmosphere before essentially swan diving into it, head first. Some 20 maneuvers were conducted, taking Cassini well above and deep below its normal track, all along taking measurements and photos and beaming them back to Earth as quickly as possible. Some of those photos showed off a hurricane at the planet’s north pole area, a massive, raging storm that has been spinning for centuries (most likely) without losing steam. The storm is roughly the size of our entire planet. (Source: Mother Nature Network)
14. While Cassini was diving through the rings, it made another discovery: There’s nothing there. The ring stack around the planet is not filled with debris or anything like that; the space between the rings is nothing. At all. Just void. No other spacecraft had played hide-and-seek with the rings before, let alone flying just above or slightly below the rings. Cassini was equipped with particle detectors, sampling the materials in the rings and sending back data on the ice, debris, rocks and other materials that make them up, information scientists hope will provide clues on their origins and age of creation. (Source: NASA/JPL)
15. If you’ve ever worked a swing-shift job, where you’re working during the day one week and nights the next, it’s obvious how much an irregular sleep pattern can mess with you. Imagine if that were the case with the sun? During its time hanging around Saturn, Cassini noted that the planet has an irregular day—it doesn’t take the same exact amount of time to spin on its axis, like Earth’s 24-hour (ish) rotation. Some “days” are 10.6 hours long, others are 10.8 hours. Granted, that’s not a huge swing, but it drives scientists batty. A day is typically a nice, reliable, predictable amount of time; when it’s not it leads to discrepancies in research, imprecise calculations and conclusions based on strong hypotheses that cannot be fully tested and verified. Instead, they’ll have to look for other patterns and sift through the information Cassini sent back to come to conclusions. (Source: NASA/JPL)
16. Good vibrations, indeed. We might need a little more time to learn about the age of Saturn’s first rings, and we’ve learned a lot about the nothingness between them and the moons that hide within, but Cassini also provided insight into why some rings appear rippled or wavy. Turns out, the planet vibrates. It’s a natural occurrence that happens over the course of a few hours at a time, but it’s enough to cause the rings to ripple. Can you imagine the wavy read-out of a whole planet, millions and millions of miles away, looking like a seismograph after an earthquake? The smarties at NASA call this Kronoseismology and use it to draw insight about Saturn’s inner workings, much like seismology studies the movement of Earth’s plates and helioseismology studies the deep layers of lava and nuclear fission inside the sun. (Source: Wired)
17. As Cassini plummeted through Saturn’s atmosphere, sending back data until the last possible nanosecond, it gave scientists one more bit of brand new information. Back in the 1980s, the Voyager probe first hit on the concept of “ring rain,” that the rings around Saturn dropped material down onto the surface from time to time. This “ring rain” was believed to also prompt changes in the planet’s atmosphere, but there was no way to know for sure. Until Cassini, that is. Cassini was able to detect where the high atmosphere began and the rings ended and, as a result, it took direct, immediate measurements and collected evidence that the rings were, in fact, shedding molecules into the atmosphere, including methane. (Source: CNN)