“If you were to stack Cassini up against all over missions ever flown, the only one you could say did more is Voyager,” Trina Ray, Senior Science Systems Engineer for the Cassini team at NASA, told IFLScience. “Cassini has far surpassed its original goals.”
Those original goals were extensive. Cassini, the size of a car, was expected to study Titan, Saturn’s magnetosphere, its icy satellites, its ring system, and the planet itself all in its four-year primary mission. A delicate dance of orbits made this possible, as did the Huygens lander. Subsequent mission extensions have only increased the goals.
On Christmas Day 2004, Huygens was released from the Cassini spacecraft. It entered the atmosphere of Titan on January 14, 2005, descending to the surface with the help of a parachute, where it returned the first ever images from the surface of a world in the outer Solar System. Huygens remains our only landing ever in this region.
Huygens returned images of smoothed pebbles, likely caused by liquid. By bouncing radio waves off the ground on Titan, Cassini was later able to discover the presence of vast lakes and seas on its surface, made up of liquid hydrocarbons. Aside from Earth, Titan is the only world we know to have bodies of liquid on the surface.
Arguably Cassin’s greatest discovery came back in 2005. This was when it first spotted plumes of icy particles coming from the south pole of Saturn’s moon Enceladus. This astounding discovery proved there was an ocean of liquid water under this moon, with the plumes providing an incredible opportunity to directly sample it.
“Everybody was just blown away,” said Ray, recounting the moment she first heard about it in February 2005. “We thought something had gone wrong with one of the instruments. We were like, ‘what? There are cracks that are hot, and the material above them is water? Are you kidding me?’”
Such was the excitement around Enceladus that NASA is already looking into sending a mission back there in the future – the tentatively named Enceladus Life Finder. It’s thought the ocean may have some of the conditions necessary for life. This spacecraft would seek to work out if that’s true.
The spacecraft also took a close-up look at the bizarre two-toned moon Iapetus, revealing that material as black as tar on one side may be dust from another moon, Phoebe. And it also revealed the aurora of Saturn.
“I think my fondest memory of the Cassini mission was realizing that we had passed through the source of Saturn Kilometric Radiation, radio emissions associated with Saturn's auroras,” Bill Kurth from the University of Iowa, a member of Cassini's Radio Plasma and Wave group (Radio and Plasma Wave group), told IFLScience.
“This represented the first time such a radio source region had been sampled directly other than at Earth.”