Illustration of Cassini spacecraft orbiting Saturn.
Frequently, it's the start of a journey, especially one into space, that generates the biggest impact. It isn't often that people remember how one ended.
Mission planners decided to finish the Cassini research mission to Saturn by dropping the 12-ton spacecraft into a fiery death dive through the planet's atmosphere. It marked a surprisingly sentimental end to a flight that left scientists with an unexpected wealth of information about Saturn and its vast system of moons.
One of the earliest motion pictures about Saturn featured photographs taken at Lowell Observatory near Flagstaff in the early 1950s.
Forty-five years later, the ambition behind Cassini made it a mission with unusually high stakes: a 3.2 billion dollar trip to a world 800 million miles away, taking seven years to complete, requiring four gravity assisted course changes for a 12 ton spacecraft carrying more than a dozen scientific measurement packages.
Amanda Hendrix with the Planetary Science Institute in Tucson describes it as a once-in-a-generation opportunity.
"This was a mission to explore the Saturn system because all we had done before that was flybys of the whole system," said Hendrix. "And what we ended up launching was a really great spacecraft."
On July 1, 2004, Cassini became the first man-made object to be guided into orbit around the most mesmerizing planet in the solar system.
"On each orbit, it would do something," commented Hendrix. "It would study the rings, or the planet itself, but on many of the orbits it would fly by one of the moons."
That's where Cassini made its biggest discoveries. Scientists already knew Saturn's largest moon, Titan, had an atmosphere. When Cassini parachuted a lander on Titan's surface, it revealed the moon featured lakes of liquid hydrocarbon.
However, Hendrix remembers, it's what the spacecraft found on another moon, ice-covered Enceladus, that still has researchers talking.
"All the other instruments detected water vapor, other types of gases, water particles, coming out of the south pole. So, we discovered all this geologic activity, this plume, really unexpected and really exciting."
Mission controllers mark the end of the Cassini mission to Saturn.Hendrix notes mission planners had expected Cassini to collect its data at the Saturn system for four years. But its nuclear-powered design let scientists successfully lobby for two extensions. The mission continued into 2017.
"People spent their entire careers working on it," she said."Some people who worked on the design and then the whole execution of (the mission) spent decades on it. That's a long time. So, we grew very close to it, and really fond of the spacecraft and its discoveries."
The decision to plummet Cassini into Saturn delivered an uncommonly emotional punch for the scientists and engineers who had devoted so much time to the remarkable journey.
Cassini's follow ups to Saturn could include a quadcopter drone that would fly above the lakes of Titan to look for life. Another spacecraft could uncover the mystery about the reduced amount of radiation around Saturn. Ironically, some scientists speculate the flashy rings might now be the least intriguing thing about the planet.
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