The Cassini spacecraft has taken a close look at a vast storm system within the hexagonal weather pattern at the north pole of Saturn. The storm looks very like a hurricane on Earth, but it is much bigger: the clear central eye of the storm is about 2000 km across – ten times the typical size on Earth – and clouds at the outer edge of the hurricane on Saturn are moving at more than 500 kph – rather faster than on Earth! One difference from terrestrial hurricanes is that this storm is locked into the weather system at the pole, rather than sweeping round the planet as happens on Earth.
The existence of this storm poses questions about both Saturn and Earth. Terrestrial hurricanes get their energy from warm ocean water; this system on Saturn does not have a handy warm ocean, although it does use a relatively small amount of water vapour within the hydrogen atmosphere. Understanding how this storm system evolves may shed light on the mechanisms of terrestrial storms.
Cassini is a joint project of NASA, ESA and the Italian Space Agency and has been observing Saturn since 2004. Scientists have not seen the north pole so clearly in the past because it is only now emerging from winter. Cassini’s composite infrared spectrometer and visual and infrared mapping spectrometer detected the great hexagonal vortex, but now it is visible. Cassini is also getting better views of the poles because it is following more highly inclined orbits, using Titan’s gravity to change the angle.
This image is published in the June 2013 issue of Astronomy & Geophysics.