lundi 9 mai 2016

The eye of Saturn’s storm & Hard Knock Life












NASA & ESA - Cassini-Huygens Mission to Saturn & Titan patch.

May 9, 2016

The eye of Saturn’s storm


Sitting at Saturn’s south pole is a vortex of monstrous proportions. The dark ‘eye’ of this feature is some 8000 km across, or about two thirds the diameter of Earth.

This image is 10 times more detailed than any previous picture of the polar vortex and shows a level of detail inside the eye that was not previously observable. Earlier images showed towering clouds around the edge of this vortex, but inside the air was thought to be mostly transparent. Here, however, a multitude of features is revealed.

Clouds are produced by convection – warm, rising gases in the atmosphere of Saturn. As they reach higher, and therefore colder, layers of the atmosphere, the gases condense and appear as clouds. At the 10 o’clock position, a stream of upwelling gas has created its own smaller vortex inside the larger one.

This view is an adjusted composite of two frames taken by the Cassini spacecraft on 14 July 2008. Cassini actually captured the scene from an oblique angle, some 56º below the plane of Saturn’s rings – a far cry from the view directly over the south pole. The orbiter was about 392 000 km from the planet at the time, yet Cassini’s camera still provided a resolution of 2 km per pixel.

Cassini spacecraft

Towering eye-walls of cloud are a distinguishing feature of hurricanes on Earth. Like earthly hurricanes, the eye of this storm is composed of warmer gas than the surroundings. However, whereas hurricanes are powered by warm water and move across the surface of our planet, this vortex has no liquid ocean at its base and remains fixed to Saturn’s south pole.

Round, swirling vortices are part of the general circulation in the atmospheres of all four giant, outer planets, and Cassini has spied many mobile ones rolling through Saturn’s clouds at other latitudes. While vortices are often informally referred to as storms, scientists generally reserve that term for bright, short-lived bursts of convection that punch though the clouds, often accompanied by lightning. 

In addition to being a thing of beauty, the vortex provides astronomers with a way to look deep into the planet’s atmosphere.

Hard Knock Life


Life is hard for a little moon. Epimetheus, seen here with Saturn in the background, is lumpy and misshapen, thanks in part to its size and formation process. Epimetheus did not form with all of those craters in place -- rather, bombardment over the eons has left this tiny moon's surface heavily pitted.

Epimetheus (70 miles or 113 kilometers across) is too small to have sufficient self-gravity to form itself into a round shape, and it has too little internal heat to sustain ongoing geological activity. Thus, its battered shape provides hints about its formation, and the myriad craters across its surface bear testament to the impacts it has suffered over its long history.

North on Epimetheus is up and rotated 5 degrees to the left. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Dec. 6, 2015.

The view was obtained at a distance of approximately 1,670 miles (2,690 kilometers) from Epimetheus. Image scale on Epimetheus is 520 feet (160 meters) per pixel.

The Cassini-Huygens mission is a cooperative project of NASA, ESA (European Space Agency) and the Italian Space Agency. JPL, a division of Caltech in Pasadena, manages the mission for NASA's Science Mission Directorate in Washington. The ultraviolet imaging spectrograph was designed and built at the University of Colorado, Boulder, where the team is based.

For more information about the Cassini-Huygens mission visit http://saturn.jpl.nasa.gov and http://www.nasa.gov/cassini. The Cassini imaging team homepage is at http://ciclops.org and ESA's website: http://www.esa.int/Our_Activities/Space_Science/Cassini-Huygens

Images, Text, Credits: ESA/NASA/JPL-Caltech/Space Science Institute/Tony Greicius.

Best regards, Orbiter.ch

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