From Fukushima to the darkest corners of the ocean, robots built for extreme environments and an appetite for discovery continue to enlighten our understanding of places too dangerous to tread. Those launched into deep space may be the most daring examples, continually pushing the limits of human ingenuity and expanding our understanding of the universe. In this series New Atlas will be profiling space probes, both past and present, tasked with pushing the boundaries of science by leading us into the great unknown. This week: the spacecraft built to study Saturn and its surroundings in one of our most ambitious space missions to date.
Name: Cassini
Launched: October 1997
Subject of study: Saturn
Current location: Cassini has become one with Saturn
Three probes had visited Saturn before NASA’s Cassini probe rolled into the area in 2004, but none had ever entered its orbit. By doing just that and continuing to circle the gas giant until 2017, Cassini has fundamentally changed our understanding of Saturn, its rings and its many moons. And thanks to the mass of its data that scientists are yet to dig into, it will continue to do so for some time yet.
“Our spacecraft is gone, but the science continues.” Thus reads the NASA team’s Twitter bio for the Cassini probe, which burned up in the atmosphere of Saturn back in 2017. The spacecraft spent 13 years in orbit around the planet and 20 years total in space, far exceeding the four-year plan of its creators at the outset.
Cassini launched in 1997 together with the ESA’s Hyugens lander, both traveling as one toward Saturn until separating in December 2004. At that point, Hyugens parachuted down to the surface of Saturn’s largest moon Titan, pulling off the first ever landing in the outer solar system and returning data for a period of around 90 minutes.
Cassini had been in orbit around Saturn for around six months by this stage, and had already spearheaded the discovery of new moons in Methone, Pallene and Polydeuces. Others would soon follow in Daphnis, Anthe and Aegaeon, but there were a couple of Saturnian moons in particular to pique the interest of the scientific community.
Working with measurements taken by Cassini, scientists learned pretty early on in the mission that Saturn's moon Enceladus was bound by a thin atmosphere with a high concentration of ionized water vapor. A close fly by of Enceladus in 2008 took the Cassini spacecraft through giant plumes erupting from the polar region and carrying water, carbon dioxide and hydrocarbons out into space.
These kinds of observations, along with the discovery of a salty subsurface ocean in 2014, have led scientists to conclude that Enceladus is one of the most likely places in the solar system to harbor some form of alien life. And we may be closer to the start of this line of enquiry than the end, with scientists reporting just last week the discovery of yet more organic molecules erupting from the surface of this icy moon.
Titan is another Saturnian moon of considerable interest to scientists, and one that we wouldn’t see the same way today were it not for Cassini. The probe has returned data on this, Saturn’s largest moon, that has led to the discovery of massive ice clouds above the south pole, methane seas and rain, deep dunes and tall mountains, along with the clearest ever views of the moon’s surface. In all, Cassini presented us with one of the more Earth-like bodies we have ever come across.
As for the ring system, the probe has captured countless stunning images and fascinating insights about the planet’s famous discs by diving right through the thick of them. This includes the revelation that the rings are shedding an astonishing amount of material and may disintegrate entirely within 100 million years. Saturn’s many moons, meanwhile, seem to be scooping up the rings’ material and growing into weird shapes.
And as for Saturn itself, the Cassini probe has shown us the planet’s polar storms in new detail, helped us precisely calculate the length of a Saturnian day and recently revealed an interior where conductive liquids appear to flow like honey.
Cassini finally met its demise in 2017 when mission control commenced what it called A Grand Finale, in a way another mission in itself. This new orbital path took the probe high above Saturn’s poles, beyond its narrow F ring, past Titan for a final time and then in between Saturn’s atmosphere and innermost ring a total of 22 times. Finally, Cassini plunged into the atmosphere and burned up like a meteor, continuing to return data to Earth until the very end.
Cassini’s scientific achievements over the course of a 20-year career in space are too many to list here, this is really just a snapshot of the ways it has furthered our understanding of Saturn and its surroundings. But it is certainly, by most measures, one of the most inspiring and successful space missions humankind has ever embarked upon. And with scientists expecting its data to continue bringing about new discoveries for decades, it is very likely that the best is yet to come.
For more on pioneering space probes, you can check out previous instalments of "Into the great unknown" on the NASA Parker Solar Probe and the Soviet Union's Venera probes. Next week, we look at Voyager, humankind's most epic astronomical adventure.