Why Cassini had to Die

This morning, the 15^th September, after 20 years in space, Cassini ended her mission exploring the Jovian and Saturnian systems, intentionally vapourising itself by crashing into the atmosphere of Saturn. Due to the huge distance they had to be relayed, signals of the data collected right up until the moment of destruction took several hours to reach Earth.

Artistic visualisation of Cassini starting her final plunge towards Saturn (Credit: NASA)

The death of Cassini was of utmost importance for the Planetary Protection of the outer solar system (see PPOSS.org). The more Cassini’s observations have taught us about the icy moons of Saturn and Jupiter, the more we have realised just how complex, interesting and important these extraterrestrial worlds are.

Enceladus, Europa and Ganymede are all now known to contain vast internal water oceans under a protective icy shell, Titan has a complex atmosphere full of organic molecules and lakes of hydrocarbons on its surface. There is a chance that these environments may harbour life or at least have complex systems of pre-biotic chemistry. In this respect Cassini created more questions than it answered, creating massive interest in further exploration of these bodies, with specific life detection missions.

Cassini discovered Enceladus has a subsurface ocean and water vapour plumes which contain organic matter and evidence of water-rock interactions - the building blocks and  a potential energy source for life (Credit: NASA)

Cassini saw through Titan's thick hazy atmosphere to discover  a hugely complex world with hydrocarbon lakes, methane rain and active geology (Credit: NASA)

In order for future missions to study these questions, we must not contaminate these bodies with terrestrial microbes or organic contaminants which may accidentally be detected and mistaken for indigenous alien life. This is where planetary protection comes in. Cassini was dirty, not having undergone strict contamination control cleaning procedures and so will have been carrying an unfortunate payload of microbes and organic molecules. If Cassini had been allowed to continue its orbit around Saturn unchecked, its orbit could have decayed over time leading to a crash landing on one of the moons which may have led to uncontainable and irreversible contamination.

Cassini’s fiery death therefore saves the pristine conditions on these fascinating moons for future generations of scientists to explore. 

Goodbye Cassini and thankyou

Artistic visualisation of the Cassini's final moments burning up in Saturn's atmosphere (Credit: NASA)