* Astronomy

 Cassini Shows Why Jet Streams Cross-Cut Saturn

Turbulent jet streams, regions where winds blow faster than in other places, churn east and west across Saturn. Scientists have been trying to understand for years the mechanism that drives these wavy structures in Saturn's atmosphere and the source from which the jets derive their energy.
In a new study appearing in the June edition of the journal Icarus, scientists used images collected over several years by NASA's Cassini spacecraft to discover that the heat from within the planet powers the jet streams. Condensation of water from Saturn's internal heating led to temperature differences in the atmosphere. The temperature differences created eddies, or disturbances that move air back and forth at the same latitude, and those eddies, in turn, accelerated the jet streams like rotating gears driving a conveyor belt.
A competing theory had assumed that the energy for the temperature differences came from the sun. That is how it works in the Earth's atmosphere.
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Updrafts of Large Ammonia Crystals in Saturn Storm

This false-colour infrared image, obtained by NASA's Cassini spacecraft, shows clouds of large ammonia ice particles dredged up by a powerful storm in Saturn's northern hemisphere. Large updrafts dragged ammonia gas upward more than 50 kilometres from below. The ammonia then condensed into large crystals in the frigid upper atmosphere. This storm is the most violent ever observed at Saturn by an orbiting spacecraft.
Cassini's visual and infrared mapping spectrometer obtained these images on Feb. 24, 2011. Scientists colorized the image by assigning red to brightness detected from the 4.08-micron wavelength, green to brightness from the 0.90-micron wavelength, and blue to brightness from the 2.73-micron wavelength. Large particles (red) reflect sunlight well at 4.08 microns. Particles at high altitude (green) reflect sunlight well at 0.9 microns. Particles comprised of ammonia -- especially large ones -- do not reflect 2.73-micron sunlight well, but instead absorb light at this wavelength.


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Credit:    NASA/JPL/Univ. of Arizona

The storm here shows up as yellow, demonstrating that it has a large signal in both red and green colours. This indicates the cloud has large particles and extends upward to relatively high altitude. In addition, the lack of blue in the feature indicates that the storm cloud has a substantial component of ammonia crystals. The head of the storm is particularly rich in such particles, as created by powerful updrafts of ammonia gas from depth in the throes of Saturn's thunderstorm.

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Cassini and Telescope See Violent Saturn Storm

NASA's Cassini spacecraft and a European Southern Observatory ground-based telescope tracked the growth of a giant early-spring storm in Saturn's northern hemisphere that is so powerful it stretches around the entire planet. The rare storm has been wreaking havoc for months and shooting plumes of gas high into the planet's atmosphere.
Cassini's radio and plasma wave science instrument first detected the large disturbance, and amateur astronomers tracked its emergence in December 2010. As it rapidly expanded, its core developed into a giant, powerful thunderstorm. The storm produced a 5,000-kilometer-wide dark vortex, possibly similar to Jupiter's Great Red Spot, within the turbulent atmosphere.
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Saturn from Cassini's VIMS spectrometer.



Animation of southern hemisphere of Saturn from distance ~1.1 mil. km, made from 21 image cubes in observation VIMS_063RI_SUBML05MP001.
Images were resampled to size 360x360 from original 64x64 size (real original resolution ~500 km/pix).
Colors are from channels 351 (R, Saturnian thermal radiation), 225 (G) and 96 (B). 5.11 (R), 3.01 (G) and 0.88 (B) in microns. Timewarp ~400x.
Date: 3.4.2008. Time: 16:01:48 - 22:37:43./