To conclude a 13-year assignment, the Cassini exploratory satellite plunged into Saturn on Sept. 15, completing its fifth and final mission around the Jovian planet, its picturesque rings and its 62 moons.
As space junkies say goodbye to this little explorer more than 1 billion miles from home, we should look back on Cassini’s history and significance, as well as some of its biggest discoveries from the past two decades.
A joint effort of NASA, the ESA and the ISA — featuring a total of 17 different nations — the Cassini spacecraft was one of the most effective and productive interplanetary missions ever launched. Cassini spent seven years en-route surveying Venus, Earth and Jupiter before arriving for its 13-year tenure in the Saturnian system.
The 5,000-pound probe took off from Cape Canaveral more than 20 years ago on Oct. 15, 1997. Thus, began 20 years of exploration and discovery.
On June 30, 2004, the probe, named for Giovanni Domenico Cassini (head of the Paris Astronomical Observatory and discoverer of four of Saturn’s moons), arrived in orbit around Saturn to begin 13 years of observations and experiments.
Included in this was the Huygens lander, sent from Cassini to smack into Saturn’s largest moon, Titan. During its descent, the Huygens probe took detailed pictures of Titan’s surface and measurements of the atmosphere, giving us our first glimpse beyond Titan’s atmosphere of the terrain below.
One of Cassini’s most exciting discoveries lies on the medium-sized moon of Enceladus. This ball of ice has become one of the most exciting celestial bodies in our solar system for astronomers and biologists alike. During one of its fly-bys, Cassini observed massive jets spraying miles beneath the southern pole.
Further inspection revealed that the composition of the geysers was, in fact, water. That demonstrated how the water beneath Enceladus’ surface was partially in liquid form — the only liquid water ever observed somewhere other than Earth, making it an exciting prospect for the possibility of life.
The cameras of Cassini were then turned toward Saturn’s iconic rings in an attempt to discern the composition, age and origin of the massive ring system.
The newly discovered phenomenon called “pinwheels” in the ring system gives us a glimpse of how planets might have formed from the primordial solar system.
The fringes of the rings held another oddity: The smallest outer fringe of the rings contained a veritable wall of boulders that sometimes towered more than two miles above their thin, uniform surroundings.
Scientists had a front-row seat to Saturn’s most recent major storm as it formed a light-colored band across the planet in 2010, creating a whole new feature of the planet’s surface.
Cassini captured a seven-second clip of lightning on Saturn more than 1,000 times more powerful than the worst electrical storms here on Earth, marking the first time such an event had been recorded in the solar system.
Cassini also shed light on one of the greatest mysteries of the ringed planet: its rotating hexagonal storm. The storm, itself larger than Earth, rotates once every 10 hours and changes color seasonally, from a winter blue-green to orange and yellow in the summer.
A bittersweet ending
Nearing the end of its propellant, one final gravity-slingshot around Titan flung the probe into a slow collision course with Saturn. In the interim, the probe made 22 close passes between Saturn and its closest rings through what is commonly called “The Big Empty.”
All of this work has culminated in the 76,000-mph death dive into the upper echelons of Saturn’s atmosphere.
In a statement, NASA and the ESA stated that they decided to send Cassini into Saturn to “ensure that Saturn’s moons will remain pristine for future exploration.”
The final dive took Cassini closer to Saturn than we have ever been. The data sent back during the dive will be pored over for decades to come, shedding light on the composition of Saturn’s atmosphere and the planet itself with a closer look than we are likely to get for decades.
“Cassini has been revolutionizing our views of the Saturn system since the moment it arrived, and for 13 incredible years right until the very end today,” ESA science director Alvaro Giménez was quoted as saying Monday.
The poetic closure of sending the craft into Saturn lends a bittersweet ending to this two-decade-long story of exploration.
“Things never will be quite the same for those of us on the Cassini team now that the spacecraft is no longer flying,” stated project scientist Linda Spilkner in NASA’s press release, “but, we take comfort knowing that every time we look up at Saturn in the night sky, part of Cassini will be there, too.”