Asked by Richard West

If you read our article on the Cassini spacecraft you might recall that, at the end, we said it was going to be purposefully sent crashing into Saturn in 2017 to prevent the contamination of nearby moons. But, why are they doing this? Why don’t they fire the probe out of the Solar System and carry on gathering data?

The main reason is that, by 2017, Cassini will not have enough fuel to maintain its orbit around Saturn or to reach the required speed to escape Saturn’s orbit, let alone the Solar System. Although small, there’s a chance it would be pulled back into the Saturnian system and impact one of the moons. If we plan to one day explore the surface of these moons, which may have some evidence of past or present extraterrestrial life on their surfaces, such a collision would contaminate said moon and possibly give us incorrect data on a future mission.

Another reason to send Cassini into Saturn is that it will be a good opportunity to get data from the atmosphere that no probe has got before. We’ll be able to study Saturn’s cloud tops up close and take readings as the probe enters the atmosphere, something that probably won’t be repeated for many decades.

Image courtesy of NASA and JPL-Caltech