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How many rings does Saturn have?
Saturn has seven rings, named in order of their discovery. However, the order from outside in towards Saturn is: E-G-F-A-B-C-D. Italian astronomer Galileo Galilei first discovered the rings in 1610, but did not know what they were - he described them as cup handles. Half a century later, Christiaan Huygens, using a better telescope, conceived the idea of a planetary ring system and hypothesised that the rings were solid, thin and flat.
If you put one end of Saturn's rings here on the Earth, the other end would reach to the moon. However, the rings are flat - their actual thickness is only 5-10m.
How were Saturn's rings formed?
Scientists hope that Cassini will answer this question once and for all. Early ideas were that the rings were bits left over from the formation of Saturn that were not able to form into a moon. Later it was suggested that the rings are the leftovers from one of Saturn's own moons that came too close to the planet and was torn apart by violent gravitational forces. A third hypothesis is that a giant meteoroid slammed into one of Saturn's moons smashing it into pieces forming the rings. No one can be certain, but the data from Cassini should help scientists discover the answer.
What instruments are on board Cassini, and what do they do?
Cassini has 12 instruments. For a comprehensive run-down see the .
What instruments are on board Huygens, and what do they do?
Huygens has 6 instruments. For a comprehensive run-down see the .
How is Cassini powered?
Cassini can't use solar power because it is too far away from the sun and no existing solar panel technology would provide the power necessary to power it. So instead it has onboard Radioisotope Thermoelectric Generators (RTGs). These produce heat using the natural radioactive decay of plutonium, and the heat is then turned into electricity by solid state thermoelectric convertors.
Where does Cassini store its data? How does Cassini send its data back?
All the data that Cassini collects is stored on the solid state recorder. Cassini-Huygens is the first deep space mission to use this kind of technology. Before, 'flight tape recorders' were used, but there are no moving parts in this recorder - hence solid state.
Cassini turns to Earth after collecting the data, and using the huge, dish shaped high-gain antenna, beams the data back as radio waves. NASA's Deep Space Antenna Network receives the data in its facilities at Goldstone, in California's Mojave Desert, near Madrid, Spain and near Canberra, Australia. This means that as the Earth rotates, the spacecraft can be constantly observed.
Cassini also has a low-gain antenna that sends back a more diffuse radio signal. This works as a back-up. During Saturn Orbit Insertion, because the main antenna was turned to face the rings using the dish as a shield to protect Cassini, the monitored signal was sent from the low-gain antenna.
Why could Voyager not stay? Where are the Voyager probes now?
The Voyager mission was designed to fly past Jupiter and Saturn. After the two probes sent back such extraordinary data, their mission was extended. Voyager 2 continued its journey to explore Uranus and Neptune, and Voyager 1 headed for interstellar space. They are still exploring and sending back data. Their current mission, the Voyager Interstellar Mission (VIM) will explore the very edge of the Sun's domain, and carry on even beyond that. They also send back data via the Deep Space Network.
What is Saturn made of?
The sixth planet from the Sun and the second largest in our Solar System, Saturn is a gas giant, like Jupiter, Uranus and Neptune. It is made primarily of hydrogen and helium (96% hydrogen and 4% helium with traces of water, methane and ammonia), and has a volume over 750 times greater than that of the Earth.
Saturn doesn't have a surface in the same way as Earth, for example. There is a gradual change from the gaseous atmosphere to liquid hydrogen and helium. As the depth increases, so does the pressure, causing the gases to change state.
How many moons does Saturn have? What are they named after? Who names them?
Saturn has 33 moons, two of which were discovered in August 2004. The biggest moons are named after characters from Greek mythology, like Pan, Atlas, Phoebe and Pandora. The smaller, more recently discovered moons are named after characters in Norse, Gallic and Innuit mythology, like Skadi, Albiorix and Paaliaq respectively. The names are chosen by the International Astronomical Union. The two new moons have yet to be named, and are currently designated as S/2004 S1 and S/2004 S2.
Why might the sky on Titan appear green?
Recent research by scientists at the Max Planck Institute suggests that from the surface the sky might appear green. The colour of anything that we see is the colour of the light it reflects. The rest of the colours are absorbed by the object. Methane is concentrated in the lower part of Titan's atmosphere, and absorbs red light. With the combination of the thick upper haze which blocks much of the Sun's light from the surface of Titan and methane absorbing the red light, it is possible that the only colour left will be green.
Could there be sources of water on Titan?
One possibility is that there are volcanoes on Titan, which can spew out water from the liquid layer that scientists think might lurk beneath its surface. Secondly, like everywhere else in the Solar System, Titan is vulnerable to impacts by comets and meteorites. Craters formed by objects of more than a kilometre in diameter would almost certainly heat the water-ice surface of Titan, resulting in a temporary melt later of liquid water in which amino-acids could be formed.
But currently Titan is simply too cold for liquid water to be present on the surface for any great length of time. However, the Sun will ultimately change. It may be that in another five billion years from now, it will turn into a red giant, where its core becomes hotter and it expands. When that happens, the Earth will be consumed, but further out from the Sun, where Titan is, it will become warm enough to melt the ice and create a water-covered planet. Because Titan is already covered in organic material, it may then become a place for life to evolve.
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