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While our own moon may be thought of as difficult for man to visit, researchers say Saturn's has a whole lot more to kill off any unsuspecting visitors.

Researchers have found gigantic polar clouds of hydrogen cyanide roughly four times the area of the UK on Titan, the largest moon of Saturn.

Astronomers say the find was 'totally unexpected'.

Nasa's Cassini spacecraft spotted the development of the gigantic polar cloud covering over one million square kilometres – roughly four times the area of the UK.

The new study led by Leiden Observatory, the Netherlands Institute for Space Research and the University of Bristol is published today in Nature. 

Titan has seasons just like Earth, only each season lasts over seven years instead of three months due to its ponderous orbit around the Sun. 

After equinox in 2009, Titan's south pole entered the perpetual darkness of polar winter. 

Soon after, instruments on Nasa's Cassini spacecraft observed the development of a gigantic polar cloud covering over one million square kilometres – roughly four times the area of the UK.

Bristol researcher and co-author Dr Nick Teanby said: 'The cloud was first seen in images from Cassini's cameras taken in 2012. 

'It started off quite small but soon grew to cover the entire south polar region. 

This was totally unexpected and set us puzzling over what the cloud could be made of.

Unfortunately, while the images showed that the cloud was very high up, at over 250km above the surface, they did not allow us to figure out what the cloud was actually made of or why it was there.

'For the next two years Cassini gathered more data including infrared spectra of the cloudy region.

Lead author Remco de Kok said: 'When we looked at the spectra, we saw two large peaks that weren't present in spectra of other places on Titan. 

Saturn's biggest and brightest moons are visible in this portrait. Titan (5,150 kilometers, or 3,200 miles across) is Saturn's largest moon and appears at the lower left. Rhea (1,528 kilometers, or 949 miles across) is the planet's second largest moon and is seen above center. Enceladus (505 kilometers, or 314 miles across) has the brightest surface in the solar system, reflecting nearly all of the sunlight that falls upon it. Enceladus is just above the rings, right of center.

These peaks coincided exactly with the peaks you'd expect from ice particles of hydrogen cyanide, or 'blauwzuur' (blue acid) as it's known in the Netherlands, which is highly toxic. 

This was very surprising to us, since we did not expect HCN ice to be able to form so high in Titan's atmosphere.

'This new research suggests that Titan's south pole must be extremely cold to allow hydrogen cyanide to condense. In fact, the upper atmosphere must have cooled by over 50 degrees in less than a year to reach a blisteringly cold -150C.

Remco de Kok concluded: 'This is a very rapid change given Titan's long annual cycle and is much colder than previously thought possible. 

It suggests that once the pole is in shadow the upper atmosphere acts as a very efficient radiator of heat, perhaps due to the high abundance of exotic hydrocarbon and nitrogen based compounds, which emit strongly in the infrared.

This artist's rendition shows the Huygens probe floating in a methane/ethane lake on Titan. A probe due to land on Saturn's moon, Titan, could discover a world that looks 'a little bit like Sweden or Northern Canada', one of the mission's scientists said.

'Cassini is set to continue observing Titan until it takes a dive into Saturn at the end of its mission in 2017. 

It will be fascinating to see how the cloud will develop.' 

Titan is unique in our solar system because of its dense nitrogen-methane atmosphere, which is very similar to Earth's in some ways, but very different in others. 

For example, air temperatures are around 200 degrees colder and, in contrast to the warm salt water seas of Earth, frigid hydrocarbon lakes populate Titan's surface.