Saturn’s ‘hot hexagon’ surprise
04 Jan 08
Saturn’s chilly north pole boasts a hot spot in the middle of its mysterious polar hexagon, according to new data from the Cassini spacecraft. The discovery could shed light on the atmospheric formations found on other planets such as Jupiter, Neptune and Mars.
Scientists already knew about the hot spot at Saturn's sunny south pole from previous observations but the north pole vortex came as a surprise. The researchers report their findings in this week’s Science.
‘The hot spots are the result of air moving towards the pole, being compressed and heated up as it descends over the poles into the depths of Saturn,’ said Leigh Fletcher, a planetary scientist from the University of Oxford and the lead author of the Science paper. ‘The driving forces behind the motion, and indeed the global motion of Saturn's atmosphere, still need to be understood.’
In their paper Fletcher and colleagues report that the bright, warm hexagon feature, first seen in the cloud tops by the Voyager spacecraft in 1980, continues to far greater heights than previous studies had shown. ‘It extends right to the top of the troposphere,’ said Fletcher. ‘It is associated with downward motion in the troposphere, though the cause of the hexagonal structure requires further study.’
‘We had speculated that the south pole hot spot was connected to the southern, sunlit conditions,’ said Glenn Orton, a senior research scientist at NASA's Jet Propulsion Laboratory and co-investigator on Cassini's composite infrared spectrometer. ‘Since the north pole has been deprived of sunlight since the arrival of winter in 1995, we didn't expect to find a similar feature there.’
Winter lasts about 15 years on Saturn. Researchers anticipate that when the seasons change in the coming years and Saturn's north pole is once again in sunlight, they will be able to see a swirling vortex with high eye-walls and dark central clouds like the one now visible at the south pole. ‘But Saturn may surprise us again,’ adds Fletcher. ‘The fact that Neptune shows a similar south polar hot spot whets our appetite for the strange dynamics of the poles of the other gas giants.’
Scientists hope to gather more information about Jupiter's poles from the Juno mission currently scheduled for launch in 2011 and arrival in 2016.
The article ‘Temperature and Composition of Saturn’s Polar Hot Spots and Hexagon’ is published in Science on 3 January. Leigh Fletcher’s research was funded by the UK's Science and Technology Facilities Council.
The Cassini-Huygens mission is a cooperative project of NASA, the European Space Agency and the Italian Space Agency. The Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Cassini-Huygens mission for NASA's Science Mission Directorate, Washington. The Cassini orbiter was designed, developed and assembled at JPL. The science team for Cassini's composite infrared spectrometer team is based at NASA's Goddard Space Flight Center.