Cassini's Grand Finale: Why NASA had to destroy spacecraft Cassini?
On September 15 of 2017, one of the best probes we have ever known, the spacecraft Cassini, made its final great deed. After a glorious 20 years long journey, overcoming space hazards in sake of providing us an incredible amount of data that will continue to allow wonderful scientific discoveries, Cassini disintegrated itself in Saturn's atmosphere.
Spacecraft Cassini diving through the gap between Saturn and its innermost ring. Illustration taken from the short film Cassini's Grand Finale made by NASA.
After extending its mission a couple of times, Cassini ended up making the most out of the fuel it had, the one that is needed for its course to be corrected and controlled. Cassini's mission in the orbit of Saturn was planned to last 4 years, until May of 2008. However, on April 15, 2008, the program received funding to be extended until September 2010, and later once again, for another 7 years.
In spite of running low on fuel, why Cassini had to be destroyed? It could have been left to wander in Saturn's orbit, providing data until it eventually runs out of battery, the same way it has been done with other spacecrafts in different situations. Withal, there's a special reason not to do so. NASA consciously decided to make a controlled approach into the atmosphere of Saturn, so that, the resulting disintegration of Cassini, would eliminate the possibility of an unlikely collision against, specifically, two of the many moons Saturn has. Those are Titan and, most of all, Enceladus.
As the same data provided by Cassini has revealed, both Enceladus and Titan contain more than fascinating environments. Titan, the biggest moon of Saturn, has its own atmosphere with winds and thick clouds that can produce thunderstorms near the poles and even occasional rain. That means its geography can be similar to earth. Titan is the only known object in our solar system (besides earth) to have regions of seas on its surface. A consideration though: rain and seas are not made by water but by liquid methane (temperatures are low enough for that). Although life as we know it could not exist now in Titan since it doesn't have liquid water, complex organic molecules are strongly argued to exist there. Titan is thought to be a prebiotic environment or possibly a biotic environment, so come kind of life is not impossible to happen at Saturn's mayor moon. Enceladus, on the other hand, almost doesn't have atmosphere but its peculiarity is due to the large geysers Cassini discovered over its south pole. After that finding, the spacecraft's mission was modified to include a close and difficult approach to Enceladus in order to capture and analyze the particles being ejected by those geysers directly to space. The risky maneuver was perfectly executed and the substance was proved to be water. Due to Enceladus icy surface, sunlight is mostly reflected making for an extreme low temperature there. However, those enigmatic geysers are telling there is an important source of geological heat at the heart of the Enceladus. That condition is likely to maintain an underground ocean of liquid water where life could develop, as well as providing the energy required for life.
Spacecraft Cassini on its approach to Saturn's moon Enceladus. Large geysers over the south pole of Enceladus eject water to space. Illustration taken from the short film Cassini's Grand Finale made by NASA.
In order to protect potential life and future investigations, it is of huge importance to ensure those moons will not be contaminated. For the sake of that, Cassini disintegrated itself. Its particles became a part of the planet to which it dedicated its lifetime of exploration and success. Who would have thought its own discoveries set its finale implying it had to die. But that finale couldn't just be it and so, on its path to disintegration, Cassini made an outstanding play. Its approach to Saturn's atmosphere was planned to be an awesome mission. The Great Finale, as it was called, consisted of 22 dives into the gap between Saturn and its rings and, on the entry to the atmosphere, it required Cassini to struggle against the increasing friction to keep its antennas pointing to earth even while starting to lose its most fragile and exposed pieces. The performance of Cassini, on this one last mission, turned out to be remarkable. It allowed us to get an awesome perspective of the rings, surface and poles of Saturn. Not to mention that the final seconds of Cassini were a truly epic battle on which it succeeded to provide valuable information of the atmosphere of Saturn by keeping its antennas towards earth till the end. A glorious finale like no other.
Spacecraft Cassini on its entry to Saturn's atmosphere prior its disintegration. Using its attitude control thrusters, the spacecraft struggles to keep its antenna pointed at Earth while it sends its final data, including the composition of Saturn's upper atmosphere. Illustration taken from the short film Cassini's Grand Finale made by NASA.
Exceeding all expectations, this exceptional probe gave us amazing data to better understand, not only one incredible world called Saturn, together with its iconic rings and enigmatic moons, but also the history of our solar system, the process of planet formation and even things regarding the understanding of our whole universe. Good bye spacecraft Cassini! Without a doubt, all of us who appreciate the power of knowledge, science and exploration, feel you like a friend! You definitely are!
By Matías Lago