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Last Updated: Monday, 2 August, 2004, 14:58 GMT 15:58 UK
Cassini peers into Titan's haze
Titan's haze is thought to form when ultraviolet light breaks down molecules like Nitrogen

The Cassini spacecraft in orbit around Saturn has peered closer at the moon Titan to reveal two thin, outer layers of haze high in its atmosphere.

Mission scientists say observations like this one will help them understand how the murky haze around Titan forms.

Cassini will release its piggybacked Huygens probe on to Titan in December.

The haze has long hindered scientists in their understanding of the surface of this large Saturnian moon, which could harbour oceans of hydrocarbons.

But they are hopeful that further flybys will unlock more of the moon's mysteries.

Cassini will conduct another pass on 26 October, during which it will come 30 times closer to the planet than it did during its 2 July pass (when this image was taken).

Complex chemistry

It is not known exactly why there are two haze layers on Titan. But the moon's haze is thought to begin high in the atmosphere, at altitudes above 400 kilometres (250 miles) where ultraviolet light breaks down methane and nitrogen molecules.

Scientists believe the products of this process then react to form more complex organic molecules containing carbon, hydrogen and nitrogen that can combine to form the very small particles seen as haze.

Scientists want to understand the chemistry of Titan's atmosphere because it is thought, in many ways, to be similar to that of Earth's around four billion years ago.

It is therefore thought that the kind of chemistry occurring on Titan today may be similar to that which created the conditions for the appearance of life on Earth.

The bottom of the detached haze layer is a few hundred kilometres above the surface and is about 120km (75 miles) thick.

The image was taken with a filter that is sensitive in the ultraviolet range of the spectrum. The haze layers have been given a false purple hue to highlight them.

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