The NASA/ESA spacecraft Cassini against the backdrop of Saturn's rings In 2004 a NASA/ESA spacecraft called Cassini entered orbit around Saturn, and in the subsequent 9 years it has revolutionised our knowledge of this ringed giant and its accompanying moons. Saturn is impressive – the true ‘lord of the rings’ – and the many images produced by this 2.5 tonne spacecraft have been stunning. It is anticipated that the Cassini mission will end in 2017, with a planned suicidal dive into Saturn’s atmosphere.
One of its principal scientific targets of interest has been Saturn’s largest moon Titan, measuring about 5,150 km (3,200 mile) in diameter. Unlike the other Saturnian moons, Titan is veiled in a thick atmosphere as can be seen in the accompanying image. As a consequence, the surface cannot be seen by visible band cameras, so a long-term project for the Cassini operators has been to use the spacecraft’s main antenna as an imaging radar to penetrate the clouds to reveal the landscape beneath. This has shown a terrain remarkably Earth-like in appearance, with mountains, valleys, rivers and lakes. Clearly erosive processes very similar to those on Earth are occurring on Titan, but with a surface temperature around-200 degrees Celsius, erosive processes driven by liquid water
cannot be responsible for shaping the landscape. Remarkably, it was soon realised that, at these cryogenic temperatures, liquefied gas must be the driving force. In particular it is predominantly liquid methane (in combination with a chemical cocktail of other elements such as ethane, propane, etc) that is responsible –
which is essentially liquefied natural gas (LNG).
One of its principal scientific targets of interest has been Saturn’s largest moon Titan, measuring about 5,150 km (3,200 mile) in diameter. Unlike the other Saturnian moons, Titan is veiled in a thick atmosphere as can be seen in the accompanying image. As a consequence, the surface cannot be seen by visible band cameras, so a long-term project for the Cassini operators has been to use the spacecraft’s main antenna as an imaging radar to penetrate the clouds to reveal the landscape beneath. This has shown a terrain remarkably Earth-like in appearance, with mountains, valleys, rivers and lakes. Clearly erosive processes very similar to those on Earth are occurring on Titan, but with a surface temperature around-200 degrees Celsius, erosive processes driven by liquid water
cannot be responsible for shaping the landscape. Remarkably, it was soon realised that, at these cryogenic temperatures, liquefied gas must be the driving force. In particular it is predominantly liquid methane (in combination with a chemical cocktail of other elements such as ethane, propane, etc) that is responsible –
which is essentially liquefied natural gas (LNG).
Saturn's moons Rhea (foreground) and Titan. In the Northern hemisphere of the moon, Cassini has discovered two large lakes of LNG. A detailed survey of the
smaller the two – called Ligeia Mare – has recently been completed showing an average lake depth of around 170 m (560 feet). Overall it is estimated that Ligeia contains about 9,000 cubic kilometres of LNG, which is about 40 times the proven reserves of oil and gas here on Earth! In the unlikely event that you could transport all this to Earth, there would not be enough oxygen in the Earth’s atmosphere to burn it all.
The second lake – called Kraken Mare – has not yet been fully surveyed by Cassini. However, Kraken appears to be about 4 or 5 times larger in volume than Ligeia with therefore perhaps 200 times Earth’s proven reserves of oils and gas.
smaller the two – called Ligeia Mare – has recently been completed showing an average lake depth of around 170 m (560 feet). Overall it is estimated that Ligeia contains about 9,000 cubic kilometres of LNG, which is about 40 times the proven reserves of oil and gas here on Earth! In the unlikely event that you could transport all this to Earth, there would not be enough oxygen in the Earth’s atmosphere to burn it all.
The second lake – called Kraken Mare – has not yet been fully surveyed by Cassini. However, Kraken appears to be about 4 or 5 times larger in volume than Ligeia with therefore perhaps 200 times Earth’s proven reserves of oils and gas.
The Ligeia Mare as revealed by Cassini. More info on the remarkable Cassini mission to Saturn can be found at http://www.nasa.gov/mission_pages/cassini/main/, and the characteristics of the spacecraft are reviewed in Chapter 7 of the book ‘How Spacecraft Fly’.
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