Cassini’s final mission

The unmanned NASA spacecraft Cassini set off from Earth in 1997 with the aim of learning more about the gas giant Saturn and its many moons. Saturn is an incredible 1.2 billion kilometres away, and it took seven years for Cassini to journey there. It has sent back many amazing photographs over the course of its mission.

Now Cassini’s fuel tanks are running low, and they’ll be totally empty by September. In the mission’s last five months, known as the Grand Finale, Cassini will actually fly 22 times through the gap between Saturn and its rings. Sometimes it will fly through the very edges of the rings and sometimes it will skim close enough to Saturn to take samples of its atmosphere – more on that later. No spacecraft has ever been this close to the planet, so the information sent back will be more detailed than anything previously recorded!

Cassini’s dives between Saturn and its rings have been saved until the end of the mission because they’re quite risky. Though it looks empty, the space between the planet and the closest ring is filled with millions of tiny floating rocks. Because Cassini is moving at an average of about 60,000 kilometres per hour – 60 times faster than a large aeroplane – even a tiny piece of rock could cause serious damage.

When they’re down to the very last drops of fuel, the scientists managing Cassini from Earth will fly it directly into Saturn itself. The spacecraft will self-destruct spectacularly, burning up in the planet’s atmosphere much like a meteor would.

So why did we send a spacecraft all the way to Saturn? Cassini isn’t just taking photographs – it’s also kitted out with instruments to measure the atmosphere and materials around Saturn. One piece of technology, called the magnetometer, was developed by a team of scientists led by Professor Michele Dougherty at Imperial College London to map the magnetic field in and around Saturn. Scientists believe they will be able to use the data that Cassini sends back to learn more about the inside of Saturn and discover how giant planets are born. They also want to take measurements of the planet’s rings, to try to work out how and when they formed.

The team was also keen to learn more about Titan, Saturn’s largest moon, so they sent a machine called the Huygens probe along with Cassini on the mission. Huygens detached itself from Cassini and landed on Titan in 2005. The information sent back amazed scientists. Many of the features on Titan looked surprisingly Earth-like, with liquid, mountains and lakeshores. It even had a thick, smoggy atmosphere – not so different from what Earth’s atmosphere might have been like shortly before life developed. Overall, the information pointed towards the possibility that Titan could support some form of simple life.

With the mission providing so much exciting information, it might seem a shame to destroy Cassini at the end of it. But the scientists are convinced that it’s the right thing to do, to ensure Cassini doesn’t collide with Titan or one of Saturn’s other moons. Such a collision might pollute the moons with bacteria from Earth. The scientists want to make sure that any life they might find there in the future is definitely native to that moon – not just life brought there by Cassini from Earth.

Watch How Did Saturn Get Its Rings? to find out how the rings have been puzzling scientists for years.