The eye of the storm, dubbed by NASA as "The Rose".
The Cassini probe in orbit around Saturn has photographed a mysterious hurricane raging at the planet's north pole.
Since 1980, when the Voyager 1 probe sent back an image of Saturn depicting a hexagonal cloud formation at the planet's north pole, astronomers had wondered what lies within. That mystery was finally answered in 2007: a massively turbulent storm, possibly endlessly raging (well, at least for 30 years), captured by Cassini's Composite Infrared Spectrometer (CIRS).
Now, for the first time, Cassini has snapped close-up, visible light photographs of the monster storm. With an eye 2000 kilometres across — just over half the width of Australia — it is 20 times the size of the average hurricane on Earth, and the clouds around the eye's outer edge move at a speed of 150 metres per second. The entire storm could fit four Earths within its hexagonal borders.
But it seems, in spite of its size, that there are many similarities between Saturn's hurricane and the hurricanes on Earth — even though Saturn has only very small amounts of water. Terrestrial hurricanes generally feed off ocean water, so scientists are keen to make a deeper study of the phenomenon to find out exactly how Saturn's hurricane uses water vapour.
The green colouring represents zones of high storm activity.
"We did a double take when we saw this vortex because it looks so much like a hurricane on Earth, But there it is at Saturn, on a much larger scale, and it is somehow getting by on the small amounts of water vapour in Saturn's hydrogen atmosphere," said Andrew Ingersoll, a Cassini imaging team member at the California Institute of Technology (Caltech) in Pasadena.
Similarities between the two planets' hurricanes include a central eye with little to no cloud cover; a high cloud "wall" at the edge of the eye; high clouds spiralling the eye; and a counter-clockwise direction in the northern hemisphere. Of the differences, Saturn's storm is, of course, much bigger and more powerful; and unlike terrestrial hurricanes, which tend to move northwards, the Saturn storm is locked in one place — presumably, the scientists say, because it is already as far north as it can get.
These images, captured on 27 November 2012, at a distance of 419,000 kilometres from Saturn, are among the very first sunlit views of the pole; Cassini arrived in Saturn's orbit in 2004 during the winter when the north pole is facing away from the sun and, since then, has been unable to line up a detailed view of the poles until now. They have been captured in the near-infrared spectrum and false-coloured: images filtered at 890 nanometres are projected as blue, images filtered at 728 nanometres are projected as green, and images filtered at 752 nanometres are projected as red, where red is low cloud and green is high.