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Cassini’s Grand Finale: an incredible legacy

This artist’s rendering shows NASA’s Cassini spacecraft above Saturn’s northern hemisphere, heading toward its first dive between Saturn and its rings on April 26 2017

A few days ago, the Cassini-Huygens probe crashed into Saturn’s atmosphere after visiting several planets and moons, and orbiting the planet itself for 13 years. It sent back one final signal before being destroyed.

The “Grand Finale” (as this stage of the mission was aptly named) not only marked the end of the physical manifestation of a great achievement for scientists from a number of countries and institutes, but also gave us a chance to observe a distant planet we have long been fascinated with.

When did the mission start and end?

The Cassini-Huygens (or simply “Cassini”) probe was part of a mission intended to explore Saturn and its moons. It was launched some 20 years ago, on 15 October 1997, in a joint effort between NASA, the European Space Agency and the Italian Space Agency. The probe was initially expected to last until 2008. After some exploration of Saturn and its moons, the program was extended and, after diving in and out of the planet’s rings more than 20 times, the detector probe finally embraced its long-delayed demise on Friday 15 September 2017.

Animation of Cassini–Huygens
Animation of Cassini–Huygens

Wait… crashed into the atmosphere? Why not reuse it?

When we hear something “crashed”, we typically picture accidents. However, this crash was intentional. To collect more information about Saturn and more data about the composition of the atmosphere of Saturn, NASA decided to make the most of the probe’s last hurrah; it was still transmitting signals to Earth via its antenna 45 seconds before the crash.

As the probe was so expensive ($3.26 billion from an official announcement) a question could be raised: why not retain it and bring it back to reuse it? The answer is that, as Cassini-Huygens had been flying across the Solar System for nearly 20 years, its fuel had nearly run out and it could not go any further; not even to its moon to land and await collection.

Is it safe to dispose of the craft by crashing it into Saturn? Will it cause any pollution or threaten any potential life on the planet?

When Cassini crashed into the atmosphere, it would have been smashed into tiny pieces due to intense friction between the atmosphere of Saturn and the probe at its high speed. The pieces would have burned out like small meteorites. Few pieces would have survived entry and reached the ground, but those that might have will be buried deeply and mixed with hot gases. As the Committee on Space Research of the International Council for Science evaluated, the conditions of Saturn’s atmosphere are not suitable to make life feasible on the planet.

Although the spacecraft has been broken up, research is still ongoing. All the data received from Huygens can be processed and shared, striving for the goal of further discoveries about the Solar System’s formation.

The team of people involved in the Cassini-Huygens mission