Cassini, a joint project between NASA, the European Space Agency, and the Italian Space Agency, has been in orbit around Saturn since 2004. And now, it’s time to say goodbye.
Launched in 1997, Cassini was originally part of an orbiter-lander pairing, called Cassini-Huygens. Cassini was an orbiter intended to study Saturn and its moons, while Huygens would land on the rocky surface of Saturn’s moon Titan. In early 2005, the lander successfully made contact with Titan’s surface and began broadcasting back to Cassini. The lander sent back valuable information to Earth, including the discovery of an underground ocean.
Cassini has been orbiting Saturn for over a decade in an elongated orbit, performing close flybys of moons such as Enceladus, Titan, Iapetus, Dione, and Rhea. The wealth of data scientists have gathered over the course of the Cassini mission is staggering: from the discovery of liquid hydrocarbon seas on Titan to icy water vapor ejected into space from the surface of Enceladus. Scientists will be studying this data for decades to come.
More recently, NASA announced on April 13, 2017, that Cassini had discovered hydrogen gas within the oceans of Enceladus. Our definition of life requires three important factors: liquid water, an energy source to feed upon, and certain chemical ingredients. This news is incredibly important because hydrogen is a form of chemical energy that life—alien microbes—could feed on. When Cassini flew through one of Enceladus’ water vapor ejections, it identified a combination of water, hydrogen (an energy source), and a mixture of chemicals. It’s becoming more and more possible, likely even, that alien life might exist in the oceans of Enceladus.
So why not keep Cassini orbiting Saturn indefinitely, if it’s still making groundbreaking discoveries? The answer: It’s running out of fuel.
The spacecraft has been in orbit of Saturn for over 10 years; it’s been two decades since it launched. Its primary mission is long over, and though it’s functioned beyond anyone’s expectations since then, it will soon shut down completely. Rather than allow it to fade
Swapna Krishna is a science and tech writer, with a weekly space column at Paste Magazine. She's written about space for outlets such as Smithsonian Magazine, Fast Company, Tor.com, and The Portalist. You can find her on Twitter @skrishna.