The Huygens lander’s batteries died two hours after it touched town. Cassini went on to unleash what Spilker describes as a fire hose of information about the ringed planet and its moons. The spacecraft revealed, through stunning images and careful measurements, hurricanes on Saturn, methane lakes and seas on Titan, and water-vapor plumes erupting on Enceladus. French remembers conducting an experiment that required bouncing a radio signal off a Titan lake that, if it were smooth enough, would reflect the transmission directly at antennas on Earth. “Imagine that you’re driving a car toward the sun and you look at the hood of your car and you see the reflection bouncing off of the hood—that’s what we were trying to do,” he said. When it worked, French fell out of his chair.
The Cassini mission was only supposed to last four years. It was extended in 2008 for another two years, and again in 2010, this time until its fuel ran out. Strange as it may sound, the plan to crash Cassini into Saturn provided an exciting opportunity. The team didn’t need to be careful with it anymore. “The engineers, who’ve been so conservative and so cautious for decades, are allowing us to use the spacecraft in ways that would just have been too dangerous, to go places we never would have been allowed—in between the rings and close to the planet’s upper atmosphere and close to the edge of the known rings—and turn the spacecraft and do maneuvers with it that never would have been allowed,” said Larry Esposito, the principal investigator of ultraviolet-imaging spectrograph, which uses ultraviolet light to create images and study gases.
“It wasn’t a death spiral,” he said. “It was a new beginning.”
Cassini has returned some strange observations from its latest orbits. Scientists are getting “almost physically impossible" readings for the dynamics of the planet’s gravitational field, which they don’t yet understand, according to one researcher. The dust particles floating between the planet and its rings are tinier than they expected, and the atmosphere is denser than they predicted. They’re seeing all sorts of structures inside Saturn’s rings—clumps and streaks and waves—they didn’t expect to find.
Mission scientists will spend the next few years analyzing this data, looking for clues to some of Saturn’s biggest mysteries. Even after a 13-year trip to Saturn, humans still don’t know how massive its rings are, a measurement that could help reveal their age. Esposito, who has studied the planet’s ring system for more than 40 years, hoped Cassini’s final plunge would provide some answers.
But first, humanity had to say goodbye. After years of anticipation, the end was quick, almost jarring. In its silence, Cassini’s stewards will go on with their days. Some mission members said they would get breakfast when it was over. Others plan to drive over to a big party at the California Institute of Technology during the day, and then to a soiree at someone’s home that night. Earl Maize, Cassini’s program director, said he might help take his grandchildren to school. His 7-year-old granddaughter recently gave him an origami Saturn. Maize wonders at how little the world knew about Saturn nearly three decades ago, and how much his grandkids know now.
“Saturn for them now is this dynamic, alive place,” Maize said. “And who knows, by the time they’re my age, what Saturn and the rest of the solar system’s going to look like.”