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The international Cassini spacecraft has found a powerful hurricane at Saturn’s north pole, surrounded by the curious rotating hexagonal band of clouds.

The spinning vortex of Saturn's north polar storm resembles a deep red rose of giant proportions surrounded by green foliage in this false-color image from NASA's Cassini spacecraft

Spectacular close-up view of Saturn’s north-pole hurricane, as seen by the international Cassini spacecraft, revealing the intricate detail of cloud formations in this dynamic feature. The images were captured by Cassini from a distance of about 419,000 kilometers from Saturn on 27 November 2012, and are the first close-up views of this storm. Image scale is 2 kilometres per pixel. In this scheme, red indicates low clouds and green indicates high ones. The eye of the hurricane spans about 2000 km and the clouds at the outer edge are travelling at 540 km/h. The hurricane shares striking similarities to those seen on Earth: both have an eye with no clouds or very low clouds at the centre, high clouds forming an eyewall, with other high clouds spiralling around the eye, and an anticlockwise spin in the northern hemisphere. Image Credit: NASA/JPL-Caltech/SSI

The images were taken by Cassini’s camera on 27 November 2012 from a distance of 418,000 – 419,000 kilometers from Saturn and are the first close-up views of this storm, which has been churning since at least 2006.

NASA’s Voyager 2 spacecraft did not have a clear view of this part of Saturn’s north pole when it flew by in 1981, although it did observe the hexagonal band of clouds that is wide enough to fit almost four Earths inside. When Cassini arrived in 2004, Saturn’s north pole was dark because it was the middle of its winter.

A hurricane, spanning some 2000 km, has been identified at the heart of Saturn’s hexagonal jet stream at the planet’s north pole by the international Cassini spacecraft. A portion of Saturn’s rings can be seen in the distance. Images with red, green and blue spectral filters were combined to create this natural-colour view, which is what the human eye would see if we were there at Saturn. The image was acquired with the Cassini spacecraft wide-angle camera on 27 November 2012 at a distance of approximately 418,000 kilometers from Saturn and at a Sun-Saturn-spacecraft angle (phase angle) of 96 degrees. Image scale is 28.6 kilometers per pixel. Image Credit: NASA/JPL-Caltech/SSI

A visible-light view had to wait for the passing of the equinox in August 2009. Only then did sunlight begin flooding Saturn’s northern hemisphere. The view also required a change in the angle of Cassini’s orbits around Saturn so the spacecraft could see the poles.

In high-resolution pictures and a movie, scientists see that the extent of the hurricane’s eye stretches some 2000 kilometers across. The hurricane – 20 times larger than the average hurricane eye on Earth – has thin, bright clouds at the outer edge travelling at 540 kilometers per hour. The eyewall winds blow more than four times faster than hurricane force winds on Earth.

This movie, made from images obtained by NASA’s Cassini spacecraft, shows the clouds of a hurricane-like storm, which circulate around the north pole of Saturn out to 88.5 degrees north latitude. Video Credit: NASA/JPL-Caltech/SSI

The hurricane looks uncannily like those we see on Earth, but on a much larger – and faster – scale.  But there are also some remarkable differences.

Strangely, the Saturnian hurricane is locked onto the planet’s north pole. On Earth, hurricanes tend to drift towards the poles, but the Saturn hurricane is as far north as it can travel, and is likely stuck there. Furthermore, Earth’s hurricanes are powered by warm ocean water, but the Saturn storm is somehow getting by on the small amounts of water vapour in the planet’s hydrogen-rich atmosphere.

Learning how these Saturnian storms use the water vapour available to them could tell scientists more about how terrestrial hurricanes are generated and sustained.

A hurricane, spanning some 2000 km, has been identified at the heart of Saturn’s hexagonal jet stream at the planet’s north pole by Cassini. The images were taken with its wide-angle camera using a combination of spectral filters sensitive to wavelengths of near-infrared light. The images filtered at 890 nanometres are projected as blue. The images filtered at 728 nanometres are projected as green, and images filtered at 752 nanometres are projected as red. The colours correspond to different altitudes in Saturn’s polar atmosphere: red indicates deep, while green shows clouds that are higher in altitude. The eye of the storm appears dark red while the fast-moving hexagonal jet stream framing it is a yellowish green. Low-lying clouds circling inside the hexagonal feature appear as muted orange colour. A second, smaller vortex pops out in teal at the lower right of the image. The rings of Saturn appear in vivid blue at the top right in this colour scheme. Image Credit: NASA/JPL-Caltech/SSI

Note

Cassini flies a set of inclined orbits only every few years. The orbit tracks require precise oversight from navigators because the spacecraft uses flybys of Saturn’s moon Titan to change the angle of Cassini’s orbit. This path requires careful planning years in advance and sticking very precisely to the planned itinerary to ensure enough propellant is available for the spacecraft to reach future planned orbits and encounters.

Source: The European Space Agency (ESA)

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