Cassini's Celestial Crash

Science Editor Matthew Byrne’s eulogy to NASA’s beloved spacecraft orbiting Saturn

8th May 2017

In April 2017, NASA decided on a final farewell mission for one of its most trusted spacecrafts: Cassini. The death knell will sound on September 15, 2017 as Cassini burns through Saturn’s Atmosphere.

Cassini-Huygens, consisting of the Cassini spacecraft and the Huygens Lander, was launched in 1997 and since then it has been on a twenty year journey through our Solar System. It had a lonely journey only consisting of flybys of Earth, Venus, and Jupiter, and it wasn’t until 2004 that it entered Saturn’s orbit. After arriving, it deployed the Huygens lander onto the surface of Titan. Using Cassini as a relay, the lander transmitted data to Earth; the first time this had been done in the outer solar system.

Cassini’s mission was to identify the structure of Saturn’s rings, observe Saturn’s gaseous atmosphere, and identify Titan’s surface and clouds. It has now transmitted more than 500 gigabytes of data and has lead to the publication of thousands of research papers. Among its contribution to Science was the discovered of new moons orbiting saturn and data concerning Saturn’s rings. It demonstrated that Titan had a water cycle similar to Earth’s, consisting of rain, rivers, and seas, and also that Titan had a Nitrogen dense atmosphere.

Cassini, was only expected to last for four years and completed its primary mission in 2008. However, powered by the radioactive decay of 32.7kg of plutonium, there was no stopping Cassini and it powered on. NASA extending its mission to include another 155 orbits around Saturn and 65 flybys of Saturn’s moons. Here it discovered bizarre radio waves, which no one is sure of and it’s unclear what they are, and a spectacular hexagonal cloud at Saturn’s pole.

However, Cassini has now truly outlived its life-expectancy, and NASA has decided on it’s last final mission, the ‘Grand Finale’: to descend into Saturn’s atmosphere. It is not a simple mission, however. Cassini, has been tasked with multiple orbits to allow scientists a better look at Saturn’s furthest ring, the mysterious polar hexagon, and through the geysers of one of Saturn’s moons: Enceladus.

After this, Cassini will begin its descent into Saturn. It will use the rest of its fuel to orbit closer and closer to Saturn. At which point no other satellite will have been closer to Saturn. Here, Cassini will gather further measurements from Saturn, looking at its rings, magnetic field and gravity. NASA will then squeeze all it can out of Cassini, asking it to send back data as it dives into Saturn’s gaseous atmosphere.

But why all the effort? Why not leave Cassini in orbit around Saturn for the foreseeable future? Especially considering Cassini cost the US and EU taxpayers $3.2 billion. Cassini could send back valuable data by continuing its orbit, and so it was an attractive option to scientists. However, Cassini will inevitably run out of fuel. After which point, it would be at risk of crashing into one of Saturn’s moons. This would be problematic as microbes may still be living on Cassini, despite being in orbit for 20 years! Scientists worry that these microbes may then contaminate any water on the moons, which may disrupt any future searches for life on these planets. Although I think NASA forgot about the lander they left on Titan...

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