Goodbye, Cassini (1997-2017)

I heard about Cassini’s Grand Finale the week before it happened. At the time, I thought it would make a wonderful blog post, but then I got busy, didn’t write about it, and even missed the actual event. Luckily, NASA posted YouTube video of Cassini’s Grand Finale (what they dubbed the final part of its mission, circling between Saturn and its innermost ring before descending into the planet’s atmosphere). Others have been posting some pretty amazing videos on Cassini, as well.

Maybe I should back up a bit—especially if you’ve never heard of the spacecraft named Cassini. Technically, “Cassini” began as “Cassini-Huygens”, a collaborative effort between the National Aeronautics and Space Administration (NASA), the European Space Agency (ESA), and the Italian Space Agency (ASI). The goal was to launch a space probe to study the planet Saturn, with its’ rings and moons. The probe part of the spacecraft was named after Giovanni Domenico Cassini, while the lander was named after Christiaan Huygens. As astronomers, Cassini and Huygens both had ties to Saturn.

Animation of Cassini-Huygens by NASA via Wikimedia Commons at https://commons.wikimedia.org/wiki/File%3ACassini-huygens_anim.gif
Animation of Cassini-Huygens by NASA via Wikimedia Commons at https://commons.wikimedia.org/wiki/File%3ACassini-huygens_anim.gif

Giovanni Cassini discovered four of Saturn’s moons—Iapetus, Rhea, Tethys, and Dione—dubbing these satellites Sidera Lodoicea (the stars of Louis) to honor the king of France. Cassini also discovered what appeared at the time to be a gap between Saturn’s A and B rings that was then named the Cassini Division. Discoveries associated with Saturn weren’t his only astronomical accomplishments, though—Cassini determined the rotation periods of Mars and Jupiter and shares credit for discovering Jupiter’s Great Red Spot as well as making other contributions to astronomy. But his connection to Saturn is what landed his name on the Cassini space probe.

Another astronomer and scientist—Christiaan Huygens is probably best known for discovering the largest of Saturn’s moons, Titan, and for discovering that Saturn had rings, but he also invented the pendulum clock and was a strong supporter of the wave theory of light. No wonder the Huygens lander was named after him.

On October 15, 1997, Cassini-Huygens launched into space. As part of its original mission parameters, the Cassini-Huygens spacecraft flew close enough to Titan that the Huygens lander could (and did at the end of 2004/beginning of 2005) detach from Cassini to land on the surface of Saturn’s largest moon to send information back to Earth. The Huygens lander goes down in history for both the first landing on a moon other than Earth’s moon and the first landing made in the outer part of our Solar System (the part of the Solar System beyond the asteroid belt). From the data scientists have received on Titan, we now know that Titan shares many similarities to Earth’s geology and meteorology—having rivers, lakes, seas, and even rain.

Cassini Saturn Orbit Insertion by NASA/JPL via Wikimedia Commons at https://commons.wikimedia.org/wiki/File%3ACassini_Saturn_Orbit_Insertion.jpg
This is an artists concept of Cassini during the Saturn Orbit Insertion (SOI) maneuver, just after the main engine has begun firing. The spacecraft is moving out of the plane of the page and to the right (firing to reduce its spacecraft velocity with respect to Saturn) and has just crossed the ring plane. The SOI maneuver, which is approximately 90 minutes long, will allow Cassini to be captured by Saturn’s gravity into a five-month orbit. Cassini’s close proximity to the planet after the maneuver offers a unique opportunity to observe Saturn and its rings at extremely high resolution. https://commons.wikimedia.org/wiki/File%3ACassini_Saturn_Orbit_Insertion.jpg

But with Huygens gone, this left Cassini flying solo. As Cassini left Huygens behind, its readings showed something odd about the moon Enceladus. Returning for a closer look, scientists discovered a huge cloud made up of water vapor and ice particles emanating from Enceladus; looking closer, scientists found that most of the material in Saturn’s E Ring actually comes from Enceladus’ eruptions. Another return to collect a sample in 2008 found that the spray coming from Enceladus contains a mix of volatile gases and organic materials, and after Cassini’s mission was extended, it continued to study Enceladus as well as complete the mission extension goal of measuring the height and breadth of protrusions coming out of Saturn’s rings.

Milestones in Cassini’s Final Week by NASA/JPL-Caltech at https://saturn.jpl.nasa.gov/resources/7756/?category=graphics
Milestones in Cassini’s Final Week by NASA/JPL-Caltech at https://saturn.jpl.nasa.gov/resources/7756/?category=graphics

Still going strong, Cassini’s mission was again extended to continue studying the Saturn system’s seasonal changes and observe its’ solstice on May 24, 2017. There would be no more mission extensions, however, and with a “Grand Finale”, Cassini flew directly into Saturn’s atmosphere to be vaporized and crushed. Scientists decided to end the mission this way because they did not want to chance contaminating places like Titan and Enceladus—locations that could potentially harbor life—with any foreign microbes from Cassini.

Cassini Grand Finale Concept by NASA/JPL-Caltech at https://saturn.jpl.nasa.gov/resources/7639/
Cassini Grand Finale Concept by NASA/JPL-Caltech at https://saturn.jpl.nasa.gov/resources/7639/

There is so much more that Cassini helped scientists around the world to discover about our Solar System. Go. Explore. See what else you can find out about Cassini and Saturn and the Universe! 

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