On September 15, 2017, Cassini’s 19 year, 11 month, 0 day, 3 hour, 12 minute and 46 second long mission ended with a plunge into Saturn, the planet it had been orbiting for 13 years. The fiery demise was not accidental, but the result of a well-orchestrated plan to ensure that the spacecraft, which was running out of rocket propellant, would not crash and pollute Saturn’s pristine moons.
The Grand Finale, as it was called, was set in motion in April 2017, when Cassini was put on an impact course with Saturn through a series of 22 orbits between the planet and its rings. The never-before explored areas provided researchers with additional information that was too risky to obtain earlier in the mission. This included detailed maps of Saturn’s gravity and magnetic fields, which will enable scientists to calculate its rotation speed. Researchers were also able to get a better estimate of the amount of material in the rings, data that may help them better understand how the planet was formed. The close encounters also allowed Cassini to capture incredibly detailed images of Saturn’s rings and clouds.
Launched on October 15, 1997, the Cassini orbiter together with the European Space Agency’s Huygens probe, spent six months collecting data on Jupiter before entering Saturn’s orbit on June 30, 2004. Before the year ended, Cassini had not only conducted a series of flybys of some of the planet’s 60+ moons, but also released the Huygens probe on Saturn’s largest moon, Titan, to collect data on its atmosphere. This was the first landing on a moon, other than our own, as well as the farthest one ever made by any human-made spacecraft. Though Huygen’ mission ended there, Cassini was just getting started.
While its original task to explore the Saturn system was scheduled to end in 2008, the spacecraft was doing so well that its mission was extended twice, once for two years, and then again for seven years. In fact, the only reason researchers decided to cut short the spacecraft’s “life” was because it was running out of fuel.
The additional years enabled Cassini to observe almost two of Saturn’s 7-year long seasons and provide researchers the first detailed data of the planet and its family of moons. These include the methane-rich seas and lakes that cover close to two-thirds of Titan’s surface, as well as the erupting geysers on Enceladus. This is the first time hydrothermal activity has been observed outside Earth. During its lifetime, Cassini traveled over 4.9 billion miles and conducted 162 flybys of Saturn’s moons. All in all, the information collected by Cassini has resulted in 3,948 science publications.
While Cassini may be gone, its contribution to planetary science will be remembered forever. As Mike Watkins, director of NASA’s Jet Propulsion Lab, succinctly puts it, “One of the greatest legacies of the mission is not just the scientific discoveries it makes, and what you learn about, but the fact that you make discoveries that are so compelling that you have to go back. We will go back and fly through the geysers of Enceladus, we will go back and look at Titan, because the Cassini findings are just groundbreaking.”
Resources: Saturn.jpl.nasa.gov, nature.com,nasa.gov