The mystery of Jupiter’s jets uncovered
At the end of March 2007, scientists all over the world observed with surprise and awe a rare change in the atmosphere of Jupiter. A giant perturbation occurred amongst its clouds and two extremely bright storms erupted in the middle latitudes of the northern hemisphere, where its most intense jet stream - reaching speeds of 600 kilometers per hour – resides. Research into these unusual storms (previous ones had been seen in 1975 and 1990) and the reaction of the jet to them, undertaken by an international team coordinated by Agustín Sánchez-Lavega, from the Higher Technical School of Engineering of the University of the Basque Country (UPV/EHU), gives a more precise idea about the origin of these current flows and likewise can help to gain a better understanding of terrestrial meteorology. The work, entitled “Depth of a strong Jovian jet from a planetary-scale disturbance driven by storms’, is the cover of the 24 of January issue of the journal Nature. The team, made up of scientists from the UPV/EHU, researchers from the Fundación Observatorio Esteve Durán in Barcelona and from several North American centres: NASA, the Jet Propulsion Laboratory, the Universities of Berkeley and Arizona, as well as the University of Oxford in the United Kingdom, amongst others, monitored the event with a spatial and temporal resolution without precedent. On the one hand, they used the Hubble Space Telescope (HST) and, on the other, the NASA telescope at the mountain tops of Hawaii and the telescopes in the Canary Islands, due to the infra-red light of which, the highest clouds and temperature changes can be observed. Moreover, also decisive was the help of a whole battery of smaller telescopes located around the Earth’s southern hemisphere, from where planet Jupiter can currently be seen in better conditions. Fortunately, the beginning of the storm was observed by the HST as a backup of the observations that the New Horizons spaceship undertook in its overflight on its way to far off Pluto. They observed how the storm grew quickly from 400 km to 2,000 km in less than 24 hours, explained Mr Sánchez-Lavega. According to the study, the very bright storms are formed amongst the deepest clouds of water on the planet, rising vigorously and injecting a mixture of ice ammonia and water up to 30 km above the visible clouds. The storms move with the maximum velocity of the jet, - more than 600 kilometers per hour, creating disturbances and generating a stele of turbulence of reddish clouds that circle the whole planet. The infrared images show the brilliant festoons that make up the storms abandoning the jet stream to leeward. Surprisingly, and despite the enormous amount of energy deposited by the storms and the mixture and whirlwinds generated thereby, the jet stream stayed practically still during all this perturbation and, when it was over, this stayed robust, despite the event suffered. The computer models simulating the progress of the phenomenon suggested that the jet stream goes deep into Jupiter’s atmosphere, to more than 100 km below the visible cloud level and where solar energy cannot reach. This confirms the results previously obtained by the Galileo probe when it penetrated Jupiter’s atmosphere in December 1995. Although the regions studied are meteorologically different, everything points to Jupiter’s jet streams going very deep and suggests that the internal energy source plays an important role in its generation, states Mr Sánchez-Lavega. The comparison of the currently observed phenomenon with the previous cases of 1975 and 1990 show surprising similarities and coincidence, although without an explanation for the time being. The three eruptions have had a periodicity of between 15 to 17 years, strange for Jupiter as they do not bear any obvious relationship with the known natural periods of this planet. The storms arose at the peak of the jet, where the velocity is maximum, not to the North or to the South and there have always been two storms (not one or more or one less) and, finally, in all cases they move at the same speed. If, at some time in the future, we are able to crack this riddle, we will know the mysteries that lie beneath Jupiter’s clouds, comments Mr Sánchez-Lavega. The atmosphere of the giant gaseous planet of Jupiter, ten times the size of the Earth and where the day lasts only 10 hours, is in a permanent state of agitation. Atmospheric circulation is dominated by a system of jet streams, alternating in latitude and that distribute their clouds in bright and dark rings parallel to its equator – all these phenomena being unexplained. The changes in the cloud rings are sometimes violent ones circling the planet. Their origin and that of the energy source generating them as well as the jet streams are all matter for controversy amongst meteorologists and planet scientists. They might be generated by the deposition of solar radiation as on Earth or by the intense internal energy source emanating from Jupiter’s interior or perhaps by a combination of both. Knowing the mechanisms that operate in these phenomena is important for terrestrial meteorology – which is home to many storms and where jet streams also dominate atmospheric circulation. In this manner Jupiter represents a natural laboratory where scientists can study the nature of and the interrelation between jet streams, storms and violent atmospheric phenomena This is the third time that a team led by Mr Sánchez-Lavega has achieved a front cover story in Nature. The previous two, in 1991 and 2003, involved investigations undertaken about Saturn.