Cassini - A Year On by Holly Thompson

This Saturday marks one year since the Cassini mission ended, which was one of the most ambitious missions that NASA has ever carried out. This fascinating investigation lasted for twenty years and gave an important insight into what’s happening around Saturn.

It seems that the majority of people’s favourite thing about Physics – whether well-versed in the subject or not – is outer space. With photos of the stars taken by the Hubble Space Telescope (HST) and sci-fi films such as ‘Interstellar’ (2004) and ‘2001: A Space Odyssey’ (1968), all this focus on the stars, planets and the Universe has almost created an obsession within our generation. We typically just want to know the answer to the question, ‘What is out there?’, therefore our curiosity is directed outside of the Solar System.

eXtreme Deep Field photo created from 10 years of HST photos of the Ursa Major Constellation. Credit: NASA

However instead of focusing on the outside of our Solar System, one of NASA’s largest missions targeted a goal much closer to home – Saturn and its moons. Saturn, in theory, is regarded as an ‘early stage Solar System’. The gas giant mimics the Sun, with the rings around it reminding us of the dust and gas that surrounded our Sun in its younger years. A more in-depth answer as to why Saturn was selected for this mission was given in a 2004 press release by Dr Ed Wieler. The administrator for NASA in Washington DC said, ‘The Saturn system represents an unsurpassed laboratory, where we can look for the answers to many fundamental questions about the physics, chemistry and evolution of the planets’ (1). In addition, Saturn has 52 moons that have scarcely been investigated, and this mission allowed scientists to study the two most prominent – Titan and Enceladus.

This mission was viewed as one of the most ambitious and riskiest investigations that NASA had ever carried out for a number of reasons: would the satellite be able to find and receive enough data to make this two-decade long, 3.5-billion-dollar exercise worth it? Additionally, the large distance from Earth meant that it would be impossible to give the satellite any instructions in real-time, so every command had to be pre-programmed to make sure that nothing went wrong whilst being 1.4 billion kilometres away. The instruments on the satellite also had to be fine-tuned so they could detect dust particles that not even the most sensitive of organic nerve endings could detect, but they also had to be robust enough to withstand travelling speeds of up to 69,000 miles per hour. Due to this, throughout the mission, over 5000 people took part within the building, programming and monitoring of the Cassini satellite, some of which had been working on the project since 1988 at its inception. When the space-craft eventually reached the gas giant on 1st July 2004, it almost immediately started to change our knowledge of the planet and its system, and was a cause for celebration among so many people in the scientific community.

Throughout a ten-year period the satellite was able to take pictures and carryout flybys of Titan, the planet’s largest moon, where ice was found to be mixed with possible organic matter, creating dark areas. It was thought, before this mission, that liquid hydrocarbons, such as methane and ethane, caused these dark areas of colour on the lighter rocky surface. However, definitive evidence wasn’t found until 2006 when, during flybys of Titan, a lake of methane in its northern pole was discovered, as were others around the moon. These were the first bodies of surface liquid, found outside of the planet Earth, which were stable.

Photo of Titan’s surface with methane lakes. Credit: NASA

However, it gets more exciting than just methane on Titan! The mission allowed us to discover the first liquid water anywhere other than Earth – it was found on the sixth moon Enceladus. The satellite sent back to NASA photos of plumes of what was thought to be a gas, and it was observed that these plumes moved about randomly. As the craft did closer and closer flybys, it was determined that these geysers were actually made of water. The movement was due to the gravitational pull of Saturn which proved the hypothesis of liquid water within the Solar System.

After these discoveries, the spacecraft had to ‘die’ on 15th September 2017 by plunging into the planet’s atmosphere, as the small amount of fuel left meant it would be impossible to control the flight any longer. The satellite was sending information back to Earth until its end, when it was finally destroyed by the atmospheric pressure.

The Cassini mission was a monumentally important outer Solar System expedition as it changed the way people look at Saturn and its moons. This discovery means that there is a possibility of very early stage life forms, which shows that life can occur in places in our Solar System other than our home planet and could potentially occur in other places in the Universe. Furthermore, so many presumptions were broken by the photographs and observations the mission sent back to Earth, and so this mission was crucial to the progression of outer system exploration, and thoroughly aided in the understanding of it.

In addition, this mission has inspired so many people to learn more about our Solar System, with NASA launching the #CassiniInspires scheme. This tag was created for people to share their artistic portrayals of what the Cassini mission meant to them online, and as a result, everything from pieces of artwork to songs to poetry were created.

A year after Cassini’s death, we hope to be seeing more unmanned outer Solar System missions from organisations such as NASA, so that they can continue to inspire people and to carry on the success of the mission in the years to come.


  1. NASA. Cassini-Huygens Will Unlock Saturn’s Secrets. [Internet]. 2004. Available from: https://www.nasa.gov/mission_pages/cassini/media/release-060304.html

When I Listened to Saturn's Rings

I listened to saturns rings. I wasn't afraid but my eyes did shift to saucers and my blood rushed in rapid little whims.

A toddler girl asked me if I would travel to space if she came along and held my hand. And of course I said yes but i knew inside I

was lying, that i was too craven. I have recurring dreams about being trapped up high with no way to get down. Just hanging there weedy and lurching. Sometimes i'm crouching

on a fragment of wood atop a tin branch at least a mile high. My knees are wobbly as if I am falling hard in love and my heart is thrusting as if i'm listening to Saturn's rings.

Poem by twitter user @silentrees

Acrylic by Eileen McKeon Butt. Credit: NASA


All images courtesy of NASA and JPL

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