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 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
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.
Jupiter is the fifth planet from the Sun and is the largest one in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains more matter than all of the other planets combined. It has a mass of 1.9 x 1027 kg and is 142,800 kilometers (88,736 miles) across the equator. Jupiter possesses 28 known satellites, four of which - Callisto, Europa, Ganymede and Io - were observed by Galileo as long ago as 1610. Another 12 satellites have been recently discovered and given provisional designators until they are officially confirmed and named. There is a ring system, but it is very faint and is totally invisible from the Earth. (The rings were discovered in 1979 by Voyager 1.) The atmosphere is very deep, perhaps comprising the whole planet, and is somewhat like the Sun. It is composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor and other compounds. At great depths within Jupiter, the pressure is so great that the hydrogen atoms are broken up and the electrons are freed so that the resulting atoms consist of bare protons. This produces a state in which the hydrogen becomes metallic.
Colorful latitudinal bands, atmospheric clouds and storms illustrate Jupiter's dynamic weather systems. The cloud patterns change within hours or days. The Great Red Spot is a complex storm moving in a counter-clockwise direction. At the outer edge, material appears to rotate in four to six days; near the center, motions are small and nearly random in direction. An array of other smaller storms and eddies can be found through out the banded clouds.
Auroral emissions, similar to Earth's northern lights, were observed in the polar regions of Jupiter. The auroral emissions appear to be related to material from Io that spirals along magnetic field lines to fall into Jupiter's atmosphere. Cloud-top lightning bolts, similar to superbolts in Earth's high atmosphere, were also observed.
Unlike Saturn's intricate and complex ring patterns, Jupiter has a simple ring system that is composed of an inner halo, a main ring and a Gossamer ring. To the Voyager spacecraft, the Gossamer ring appeared to be a single ring, but Galileo imagery provided the unexpected discovery that Gossamer is really two rings. One ring is embedded within the other. The rings are very tenuous and are composed of dust particles kicked up as interplanetary meteoroids smash into Jupiter's four small inner moons Metis, Adrastea, Thebe, and Amalthea. Many of the particles are microscopic in size.
The innermost halo ring is toroidal in shape and extends radially from about 92,000 kilometers (57,000 miles) to about 122,500 kilometers (76,000 miles) from Jupiter's center. It is formed as fine particles of dust from the main ring's inner boundary 'bloom' outward as they fall toward the planet. The main and brightest ring extends from the halo boundary out to about 128,940 kilometers (80,000 miles) or just inside the orbit of Adrastea. Close to the orbit of Metis, the main ring's brightness decreases.
The two faint Gossamer rings are fairly uniform in nature. The innermost Amalthea Gossamer ring extends from the orbit of Adrastea out to the orbit of Amalthea at 181,000 kilometers (112,000 miles) from Jupiter's center. The fainter Thebe Gossamer ring extends from Amalthea's orbit out to about Thebe's orbit at 221,000 kilometers (136,000 miles).
Jupiter's rings and moons exist within an intense radiation belt of electrons and ions trapped in the planet's magnetic field. These particles and fields comprise the jovian magnetosphere or magnetic environment, which extends 3 to 7 million kilometers (1.9 to 4.3 million miles) toward the Sun, and stretches in a windsock shape at least as far as Saturn's orbit - a distance of 750 million kilometers (466 million miles).