Science & Exploration

Cassini-Huygens Frequently Asked Questions (FAQs)

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ESA / Science & Exploration / Space Science / Cassini-Huygens

We are getting lots of comments regarding Saturn, Titan and Cassini-Huygens. Before posting any questions, please look through the following FAQs to see if your questions have already been answered.

About Cassini-Huygens

Where does the name ‘Cassini-Huygens’ come from?

The spacecraft is named after two famous scientists. The Saturn orbiter is named after Jean-Domenique Cassini, who discovered the Saturnian satellites Lapetus in 1671, Rhea in 1672, and both Tethys and Dione in 1684. In 1675 he discovered what is known today as the 'Cassini Division', the narrow gap separating Saturn's rings into two parts. The Titan probe was named Huygens in honour of the Dutch scientist, Christiaan Huygens, who discovered Titan in 1655.

Where does the Huygens probe name come from?

The Titan probe was named Huygens in honour of the Dutch scientist, Christiaan Huygens, who discovered Titan in 1655.

What are the mission objectives? What scientific return do you expect from the mission?

Cassini’s four-year mission will collect detailed data on Saturn, its rings and the 31 known moons orbiting this gas giant. The information will aid scientists in understanding this complex and fascinating region. Main scientific goals include measuring Saturn's huge magnetosphere, analysing from up close those stunning rings and studying Saturn's composition and atmosphere.

The goals of Huygens are to study the atmosphere and the surface of Titan along the descent ground track and near the landing site. Some of the questions scientists would like to answer are:


  • what is the source of heat inside Saturn that produces 87 per cent more energy than the planet absorbs from sunlight?
  • what is the origin of Saturn’s rings?
  • where do the subtle colours in the rings come from?
  • are there any more moons?
  • why has the moon Enceladus such an abnormally smooth surface? (Has recent melting erased craters?)
  • which chemical reactions are occurring in Titan's atmosphere?
  • what is the source of the methane, a compound associated to biological activity on Earth, which is so abundant in Titan’s atmosphere?
  • are there any oceans on Titan?
  • do more complex organic compounds and 'pre-biotic' molecules exist on Titan?

What makes Cassini-Huygens special?

Cassini-Huygens is an international collaboration between three space agencies. The Cassini orbiter that will orbit Saturn and its moons for four years, and the Huygens probe that will dive into the murky atmosphere of Titan and land on its surface. Huygens will be the first probe to land on a world in the outer Solar System - on the surface of Titan, Saturn’s largest moon.

The sophisticated instruments on board both Cassini and Huygens will provide scientists with vital data to help understand this mysterious, vast region. The Huygens instruments will make detailed on-the-spot measurements of Titan's atmospheric, looking at its structure, composition and dynamics. Images and other remote-sensing measurements of the surface of Titan will also be made during the descent.

Preserved in the deep freeze of Titan's atmosphere are chemical, carbon-rich compounds thought to be similar to those of Earth's primeval soup. The in situ results from Huygens, combined with Cassini's global observations from repeated fly-bys of Titan, will provide vital information towards the great mystery of how life began on Earth.

Why go to Saturn?

Scientists want to learn much more about Saturn’s atmosphere, its inner composition, its radiation environment and its history. How did the giant planet develop? What causes its lightning bolts, massive storms and whistlers? How does it magnetosphere interact with the rings and the moons? What is the secret of its perfectly aligned magnetic field?

Saturn’s magnetic field and the planet appear to rotate about the same axis. This alignment is unique among all known planets and, depending on what we find at Saturn, scientists may have to rethink their theories of how planetary magnetic fields form.

Why are we going to Titan?

Titan is one of the most mysterious objects in our Solar System. It is the second largest moon (only Jupiter's Ganymede is bigger), and the only one with a thick atmosphere. It is this atmosphere that excites scientific interest, since it is thought to resemble that of a very young Earth.

Preserved in the deep freeze of Titan's atmosphere are chemical, carbon-rich compounds thought to be similar to those of Earth's primeval soup. The in situ results from Huygens, combined with Cassini's global observations from repeated flybys of Titan, will provide vital information towards the great mystery of how life began on Earth.

Is there a risk of Huygens contaminating Titan? Will Huygens carry bacteria from Earth or pollute Titan?

The international scientific organisation COSPAR (Committee on Space Research) has established strict requirements for an adequate ‘planetary protection’. Accordingly, a planetary protection plan including the documentation of all material sent to Titan for Huygens was submitted and accepted. Given the fact that Titan is too cold and that there is no liquid water for life as we know it to evolve, the risk of contamination is practically non-existing. The harsh environment is expected to kill microorganisms that may have hitchhiked from Earth on board the clean spaceprobe.

What kind of journey is Cassini-Huygens making?

Cassini-Huygens was launched on a Titan IV-B/Centaur launch vehicle on 15 October 1997 from Cape Canaveral, USA. The large Cassini-Huygens spacecraft used four gravity-assist swing-by manoeuvres. It looped around the Sun twice. On the first loop it flew close behind Venus in its solar orbit, where it 'stole' some of the planet's orbital momentum in 1998.

The next orbit provided a second fly-by of Venus in 1999, and one of Earth later in 1999. Given these three gravity assist boosts, Cassini-Huygens finally had enough orbital momentum to reach the outer Solar System. One last gravity assist from Jupiter in 2000 gave Cassini-Huygens the final thrust of energy it needed to project itself all the way to Saturn. The mission arrives at Saturn in July 2004.

In December 2004, the Huygens probe is ejected on its 22-day cruise to Titan.

How long does it take to get to Saturn? How many kilometres has Cassini-Huygens travelled?

This journey has taken just seven years. Cassini-Huygens has travelled at an average speed of about 16.4 kilometres per second and covered a distance of about 3474 million kilometres.

When will Cassini-Huygens arrive at Saturn, and when will Huygens land on Titan?

The Huygens probe separates from the Cassini orbiter and begins its 22-day journey to Titan on 25 December 2004. On 14 January 2005, Huygens begins its descent through Titan's cloudy atmosphere, where it lands on the surface about two and half hours later.

How long will the spacecraft be operating?

After arrival in orbit around Saturn, the spacecraft will begin a four-year tour of the ringed planet, its mysterious moons, the stunning rings and its complex magnetic environment. Cassini will complete 74 orbits of the ringed planet, 44 close fly-bys of the mysterious moon Titan, and numerous fly-bys of Saturn's other icy moons including Enceladus, Titan, Hyperion, Dione, Rhea and Iapetus.

The Huygens probe will be activated just before entering the outer fringe of Titan's atmosphere. Most of the data will be collected while descending through the atmosphere, which will take 2 to 3 hours. The landing will take place at the relatively low speed of about 20 kilometres per hour. It is hoped that the probe will survive this impact for at least a few minutes and that the instruments are also able to make direct measurements of the state and composition of the landing site surface.

If the Huygens probe survives the impact with the mysterious surface, it will continue to send unique information back to the Cassini orbiter for up to two hours until its batteries expire or it is out of range. In any case, Cassini will listen to Huygens for over four hours, until it disappears below Titan’s horizon.

Is Cassini-Huygens returning images of Saturn and Titan? Are they available in real-time?

The Cassini Imaging Science Subsystem (ISS) captures images in visible, infrared and ultraviolet light. The ISS has wide-angle camera and a narrow-angle camera, which are certainly producing high-quality images. The images, like all data, will first go to the instruments’ scientific teams for the necessary processing. After that, the images will be made available to the public.

How are NASA, ESA and ASI working together on this mission?

Cassini-Huygens is an international collaboration between three space agencies: NASA, ESA and the Italian space agency, Agenzia Spaziale Italiana (ASI). Seventeen nations contributed to building the spacecraft. The Cassini orbiter was built and managed by NASA's Jet Propulsion Laboratory. The Huygens probe was built by ESA. ASI provided Cassini's high-gain communication antenna.

Will the space agencies share the data?

Yes, more than 250 scientists worldwide will study the data collected.

I have a question that is not answered in this FAQ. What should I do?

You can send your request here. Given the huge volume of questions we get every day, we cannot guarantee to answer every e-mail individually. If we receive several similar questions, we'll consider adding an answer to our current FAQs list.