2.6 Light hours from the earth hurricane-like storms lash

Spectacular Uranus images reveal gas planet is more dynamic than previously thought

It is neither the coarsest, smallest, closest to Earth or farthest from Earth, farthest from the Sun or farthest from the Sun, nor the "moon richest" or optically most beautiful planet in our solar system. Uranus cannot come up with superlatives worth mentioning. Nevertheless it pays recently in puncto weather with the stormiest of its kind. How US scientists on the 36. As the American Astronomical Society’s Division for Planetary Sciences announced last week at its annual conference in Louisville, Kentucky, they recently made a series of observations with the Keck telescope in Hawaii. Pictures, which at the same time reveal a lot about the ratselhafte weather happening there.

Although Uranus has a diameter at the aquator of "only" 51.118 kilometers (Earth: 12.756 km) and is thus considerably smaller than the gas giants Saturn and Jupiter, it is one of the Iovian (Jupiter-like) planets. Finally, the light blue gas planet – this hue is caused by the absorption of red light by its methane atmosphere – not only has 27 moons, but due to its coarser density it also has about the same mass as the two giant planets.

Monotonous, featureless atmosphere

A special characteristic of the seventh planet of the solar system, as seen from the sun, is its motion around its home star. Since its axis of rotation is inclined at 98 degrees with respect to the orbital plane, "rolls" Uranus around the sun, so to speak – and this with a speed of 6.8 kilometers per second.

Given its vast distance from the Sun – Uranus orbits at an average distance of 2.87 billion kilometers (2.66 hours of light) once in 84 years – the light blue exotic is an extremely cold celestial body, which is due to the fact that it receives only two thousandths of the solar light energy because of its 30 times greater distance from the sun compared to the earth.

Die beiden Seiten des Uranus – Bildkomposition von zwei Observationen mit dem Keck-Teleskop (Hawaii/USA). The infrared images were taken on 11. and 12. July 2004 included.

Nevertheless, Uranus is still visible to the naked eye under favorable conditions. And with the equipment available today – unlike in 1781, when the German-born Briton and then amateur astronomer Wilhelm Herschel discovered the distant satellite of the sun with his homemade telescope – not only planets of this rough order, but also their rough moons can be observed with ease.

Significant for Uranus was up to now its structureless outer surface. While other planets can at least show cloudbanks or hurricanes, Uranus always preferred to hide behind a monotonous, featureless atmosphere, which, depending on the choice of filter (other factors also play a role here), looks bluish or reddish etc. to the observer. etc. Von dem, was hinter dem Schleier steckt, wissen die Astronomen ebenso so wenig, wie von dem schwach ausgebildeten, aus 11 Ringen bestehenden Ringsystem des Uranus. Specialists agree only that it consists mainly of dark chunks up to 10 meters in diameter.

Unexpectedly active atmosphere

Now, however, U.S. astronomers have been able to take strikingly good images of the planet Uranus with the Keck Observatory, perched on the summit of Manua Kea in Hawaii. The detailed photos, which are at least a class above the Hubble Space Telescope in terms of resolution, are the result of the now time-honored adaptive optics technique.

This special procedure allows the correction of the atmospheric fluctuations by the current quantity of the image deformations and their compensation by means of computer-controlled, fast deformable mirrors, which are inserted into the beam path of the telescope giants. The result: The air turbulence in the earth’s atmosphere is virtually filtered out, the image becomes formally "deflagrated".

Picturesque surroundings: The W.M. Keck Observatory is part of the Mauna Kea Observatory at the summit of the 4200 meter high volcano Mauna Kea on Oahu, the main island of Hawaii.

Using this technique, two groups of researchers from Berkeley and Wisconsin, operating independently of each other, have now been able to resolve the ring structures of Uranus and its atmosphere with unprecedented accuracy. For this purpose, they combined several images of different infrared spectra, which were taken with three different filters. The observation was conducted in two main stages: First, the Berkeley team – and then the two Wisconsin astronomers and their group – observed the blue planet.

When the image was assembled, the surprise was complete, as the astrophotos showed Uranus to be an unexpectedly active gas giant, where stormy weather seems to be the norm. "People believe that the atmosphere of Uranus is relatively inactive. However, our images show that Uranus is undergoing what may be a dramatic transformation," says Imke de Pater, professor of astronomy at the University of California at Berkeley and leader of her team. "We do not yet know the causes. Time will tell."

A 29.000 kilometer cloud

To better visually delineate the hurricane-like weather phenomena that constantly afflict the giant planet, the researchers deliberately generated false-color images. As a result, the upper cloud layers appear female, the middle ones light green, and the lower ones a darker shade of blue. Quasi as a side effect of the "Coloring" the ring system appears reddish.

The researchers were particularly impressed by a 29.000-kilometer-long cloud structure that hovered in the northern hemisphere of the Uranus planet for more than a month before dissipating again. However, in the southern hemisphere of Uranus, according to Lawrence Sromovsky, an even older, coarser storm has been raging for several years, moving up and down over five degrees of latitude. However, there is still no explanation for this.

Despite many unanswered questions, the Keck astronomers and project scientists have every reason to be pleased, since the Uranus images are of unprecedented sharpness. "We are overwhelmed by the quality and detail of these images", said Dr. Frederic Chaffee, director of the W.M. Keck Observatory in Hawaii. "These are the best images of Uranus ever taken by a telescope. They open a new window to our understanding of this unique and special world."

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