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
away, eventually crashing into the surface of Saturn or one of its moons, though, scientists have decided to conduct Cassini’s grand finale, going out with a bang.
The reasons are twofold: First, scientists want to get every last byte of data out of Cassini before it’s lost to us. Second, as discussed, one or more of Saturn’s moons might host life. Scientists don’t want to risk harming or affecting it in any way through contamination. Cassini is a radioactive spacecraft, powered by plutonium. It’s too great a risk to let Cassini possibly fall into the surface of Enceladus or Titan.
That’s the reason for the Grand Finale, and what a finale it will be. It will begin with one last flyby of Titan; a gravity assist from that moon will change Cassini’s course and slingshot it between Saturn and its rings, providing new views of both the planet and its rings. Cassini will continue to orbit the planet in this new, close-in position, looking in particular at its north and south poles.
Finally, on September 15, 2017, Saturn will take a final dive into Saturn’s atmosphere. Scientists hope to protect as much of the spacecraft as possible during its descent, garnering as much data as they can before the spacecraft is no more. Its antenna will be used to protect the camera and other sensitive equipment, hopefully prolonging the instruments’ life enough to send valuable data back to Earth.
It’s going to be tough to say goodbye to Cassini, but it’s not over yet. It will take us on a wild ride before its spectacular end.