Giant Saturn storm reveals deep winds
1er juillet 2011
July 6, 2011 - Saturn’s giant storms, commonly called "Big white spots" are rare, only five equivalent events were recorded the last 130 years, they appear roughly every 30 years, so about one revolution of Saturn. The december 2010 event was a surprise for observers, as the latter phenomenon had occurred in 1990 (Fig. 2). Cassini and HST spacecrafts was reprogramed , but with the flexibility of ground based telescopes it was possible to follow the evolution of the convective plume over several months. The origin of the phenomenon has highlighted the winds at depths inaccessible to observers. The continuous observations obtained from the Pic du Midi by a team of the Paris Observatory have been particularly useful for the study of this unusual phenomenon. An article published in Nature this week analised the plume model developed by a Spanish team from the University of Bilbao combined with observations from ground and space.
The article published this week shows a model of the convective phenomenon appeared in Saturn’s atmosphere. This extremely violent storm rises in the dense layers of the planet (P> 10 bar) unobservable from Earth or space, because these layers are located 250km under clouds top. This is also extremely rare, a follow-up campaign was immediately organized with the ground based observatories but also with the Space Telescope and the Cassini spacecraft. This is a perfect example of the complementary of observation from ground and space of modern astronomy. This article describes in particular the first 3 weeks of this great storm, it was possible to measure a differential speed between the convective column and the disturbances swept at the speed of Saturn high clouds at this latitude (Fig. 3) . Note the important role of amateur astronomers who made an almost continuous monitoring of the morphology of the phenomenon essential for understanding, we can see the image made in the center of Paris with the Arago refractor 150 years old and still producing science (Figure 4) ! For their part professional astronomers have obtained images in UV and IR useful to locate the top of the convective plume. On the first images obtained at Pic du Midi with a filter methane, the top of the spot is not visible because it is below the thin layer of methane. See also the image of “calm” Saturn obtained before the storm (fig 1). saturn-before.jpg Figure 1 : Saturn before the great storm of 2010. Like Jupiter, Saturn is dominated by a system of latitude-dependent winds creating a network of cloud bands. There are no permanent vortex as the Great Red Spot for Jupiter. Saturn had this aspect before the eruption of a giant convective phenomenon. This image is part of ongoing monitoring of the giant planets led at the Pic du Midi and with a worldwide network of observers (1). The contribution of ground based observations is fundamental to operate and manage the space observations, all data is archived by the Virtual Observatory and Planetary Laboratory.(1) Hueso, R. et al. The International Outer Planet Watch atmospheres of giant planets node database images. Planet. Space Sci. 58, 1152-1159 (2010)Click on image to enlarge Nature, vol 393, p. 397-401. gws90_a.gif sa1990b.gif saturne-clouds.jpg saturn21avril2011.jpg
Reference A. Sanchez-Lavega1, T. del Rio-Gaztelurrutia1, R. Hueso1, J.M. Gomez-Forrellad, J. F. Sanz-Requena, J. Legarreta, E. Garcia-Melendo, F. Colas, J. Lecacheux, L. N. Fletcher, D. Barrado-Navascues, D. Parker & the International Outer PlanetWatch Team, Deep winds beneath Saturn’s upper clouds from a seasonal long-lived planetary-scale storm Nature, 7 July (2011) Contact Francois Colas (Observatoire de Paris-IMCCE, CNRS)
Dernière modification le 4 mars 2013