Why NASA's Cassini Mission Was Important
What you're looking at is the newest and currently last picture that humanity has of the gas giant Saturn. September 15, 2017, marked the end of an era for NASA and space exploration as a whole. At 7:55 a.m. Eastern Standard Time on that morning, the Cassini spacecraft, that departed on its mission to Saturn nearly 20 years prior, plunged into the giant's atmosphere and was ripped apart by the windy planet. It ended its mission as the only spacecraft ever to orbit the ringed planet. The Cassini spacecraft took over 450,000 photos of the Saturnian system, along with doing many other things. But what exactly did we get out of this mission, and why was it so important?
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Cassini was launched from Earth on October 15, 1997, aboard a Titan IV rocket and began its journey to Saturn. But it wasn't a typical trip. See, the craft weighed upwards of 5,500 kilograms, making it one of the heaviest spacecraft to ever be launched at a low Earth orbit. Taking a straight shot to Saturn would have used much more fuel, and this mission may have been over many years ago. Instead, Cassini made many flybys of Earth, Venus, and Jupiter to drastically gain speed to launch the craft toward Saturn.
Three years after the launch of Cassini, it made its flyby of Jupiter, taking the highest quality pictures of the Jovian system that we have to date. But in 2004, Cassini reached Saturn and returned this photo, marking the beginning of its official mission. When Cassini first entered the Saturnian system, it wasn't alone in a sense. See, the full name of the mission is actually the Cassini-Huygens mission, and it wasn't only by NASA. It was actually a joint mission between NASA, the European Space Agency, and the Italian Space Agency. NASA managed the Cassini craft, while the European Space Agency and the Italian Space Agency controlled the Huygens module.
The module was sent with Cassini to study Saturn's moon Titan and was separated from Cassini on December 25, 2004, which must have been a pretty cool Christmas for the engineers of mission control. About three weeks later, on January 14, 2005, the Huygens probe descended from the cloudy atmosphere and landed on the surface of Titan. The probe examined the rich nitrogen and methane atmosphere of Titan while also discovering many unique things about the moon. After analyzing the data returned to Earth from the Huygens probe, it has been noted that the features on Titan's surface are remarkably similar to the features of Earth in its early stages.
The probe snapped over 700 photos that were planned to be returned to Earth, but unfortunately, about half of all photos taken on Titan were lost. Why? Well, the radio on the Huygens probe was very small and was quite weak. In order to relay the photos and data back to Earth, it first had to transmit the data back to Cassini. The Huygens probe transmitted data through two channels, channels A and B, but due to a software problem on Cassini, it only listened to data from channel A. We knew that it only received about 350 of the expected 700 photos. Huygens took photos and acquired data for 90 minutes until it ran out of battery power.
To this date, it is the furthest landing from Earth that a man-made spacecraft has ever made. But Titan isn't the only moon of Saturn that the mission made drastic discoveries on. On February 15, 2005, Cassini made its first flyby of Saturn's moon Enceladus, and Cassini returned some unusual signals back to Earth that changed the entire mission of Cassini. Signals were being sent back to the spacecraft saying that Enceladus may have a thin atmosphere. Cassini made its second and third flybys of the moon in March and July, and they had discovered something amazing: geysers on the South Pole of Enceladus were launching water vapor hundreds of kilometers into space above the moon.
This discovery caused NASA to add 20 more flybys of Enceladus onto their to-do list. The water vapor jets flying out of Enceladus led scientists at NASA to discover the liquid water ocean under the moon's crust, meaning that there's a potential chance that there could also be life on Enceladus. The water that is being spewed out into space is also surprisingly salty, making the oceans on Enceladus strikingly similar to the oceans here on Earth. This is perhaps one of the most important discoveries that Cassini made in its 20-year lifetime. If there's a recipe for life in space, this has it.
But all that water being thrown out of Enceladus has to go somewhere, right? Well, actually, everything being spewed from Enceladus is actually the cause of Saturn's E ring. Saturn has seven separate rings: A, B, C, D, E, F, and G. It's been nearly three hundred thousand kilometers from end to end. From afar, Saturn's rings look solid, but when you examine closely, it's an entirely different story. Up close, the rings are composed of small particles of dust, rocks, and ice, ranging in size from grains of sand to as large as mountains. This is a big part of the reason why you can actually see Saturn's rings so well; light reflects off the ice and particles that compose the rings, making them appear so bright.
The B ring is the brightest and largest ring of them all. The majority of the particles in this ring are the largest ones that you'll find. It's almost as if you could land on one of them, except that they're moving at 18 kilometers per second. Cassini has taken some of the most stunning photographs of Saturn's rings, discovering things that mankind would have never seen before. Since April 2017, Cassini has been writing the last thrilling chapter of its remarkable 20-year-long story: the grand finale.
After nearly 20 years in space, Cassini slowly started to run out of fuel, and the scientists at NASA had to make a decision: either leave the craft dormant around the planet, or use Cassini's instruments to the very last second. And that's exactly what they did. In order to prevent the craft from coming crashing into Titan or Enceladus, which could potentially contaminate the planet, NASA decided to send Cassini on a 22-orbit suicide mission. A final close flyby of the moon Titan on April 22nd used the moon's gravity to reshape Cassini's trajectory so that the spacecraft could pass between Saturn and its innermost rings.
This allowed Cassini to study areas of the planet that no other craft could even think of doing. During its final five orbits, Cassini passed through Saturn's upper atmosphere, returning crucial data to Earth about what exact elements make up Saturn's atmosphere. On Cassini's final orbit, mission control plunged Cassini deep into Saturn, where it transmitted data back to Earth until the very last second. Our contact with the craft was officially lost forever.
Cassini had completed its mission and found its final resting place within Saturn, the system it had studied and become a part of for the past 20 years. The mission that was planned to only last from 2004 to 2008 ended up becoming a nearly two-decades-long journey of discovering what the universe around us is like. After nearly eight billion total kilometers traveled, this mission single-handedly discovered things about Saturn and its moons that no other craft has ever done.
Cassini was, in a sense, a time machine. It gave us a portal to see the processes that likely shaped the development of our solar system. Cassini reveals Saturn's moons to be unique worlds with their own stories to tell, inspiring our sense of wonder and enriching our sense of place in the cosmos. And in the end, what more can you ask for?
"Thank you, Cassini. The signal from the spacecraft just gone, and within the next 45 seconds, so will be the spacecraft. I hope you're all as deeply proud of this amazing accomplishment. Congratulations to you all. This has been an incredible mission, an incredible spacecraft, and you're all an incredible team. I'm going to call this the end of mission."
— Project Manager, off the net.
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