Cassini at Saturn: The End of an Era

Tuesday 17th July, 2018

Our speaker was Prof Carl Murray from Queen Mary College, University of London, who works at the School of Physics and Astronomy. He had come to talk to us about "Cassini at Saturn: The End of an Era". He is particularly interested in planetary science and in 1990 was selected to be part of the camera team on the Cassini mission to Saturn. He has worked on this team for 27 years, which is most of his research career, and has been directly involved in the discovery of two new moons and several new rings around the planet.

He began by saying that he was a schoolboy at the time of the Apollo missions and, with his local astronomy club showing many Apollo films, he soon became fascinated with anything to do with space. At one point in his career he was even fortunate enough to study images sent back from the outer Solar System by NASA's Voyager spacecraft and mentioned to us that he still looks at them today.

He then explained that the full name of the mission is Cassini-Huygens and it is a collaboration between NASA, the European Space Agency and the Italian space agency ASI. The small Huygens lander was piggy-backed on to the larger Cassini spacecraft until it was released and landed on the surface of Titan, which is the largest of Saturn's moons and the only moon in the Solar System with a dense atmosphere. The Huygens lander was named in honour of the Dutch astronomer Chistiaan Huygens who discovered Titan in the Spring of 1655. This landing on Titan was the first ever landing on a body in the outer Solar System and the first landing on a moon other than our own Moon.

Prof Murray continued by saying that by careful monitoring of the spacecraft's fuel, the Cassini spacecraft mission lasted 13 years and 76 days in orbit around Saturn. It was launched on 15th October 1997 and took well over 6 years to reach Saturn, finally reaching the planet on July 1st 2004. During its time in orbit at Saturn its trajectory was altered in order to study many of Saturn's moons as well as the planet's rings. Towards the end of the mission it even completed a number of orbits that took it in the gap between the planet and its innermost rings.

Prof Murray then told us about some of the mission highlights such as finding geysers erupting from Saturn's moon Enceladus. These come from a series of parallel fractures at the moon's south polar region that are informally known as "tiger stripes" and are thought to signify a global subsurface ocean. These emissions are also thought to be responsible for the production of a diffuse ring of water ice particles around the planet — Saturn's E-ring.

As its fuel gradually ran out it was decided to send it into Saturn's atmosphere where the pressure would eventually destroy the craft so there was no possibility it could contaminate any possible life on Enceladus. Even as it descended, on September 15th 2017, it was still able to record invaluable data about the planet's atmosphere and send its findings back to the scientists on Earth. Prof Murray ended his talk by saying that even though the mission officially ends in autumn this year, the data will be studied for many years to come.