The
atmosphere of Jupiter is the largest
planetary atmosphere in the
Solar System. It is primarily made of
molecular hydrogen and
helium in roughly solar proportions; other chemical compounds are present only in small amounts, and include
methane,
ammonia,
hydrogen sulfide and
water. The latter one is thought to reside deep in the atmosphere—its directly measured concentration is very low. The
oxygen,
nitrogen,
sulfur and
noble gas abundances in
Jupiter's atmosphere exceed solar values by a factor of about three. The atmosphere of Jupiter lacks a clear lower boundary and gradually transitions into the fluid interior of the planet. From lowest to highest, the atmospheric layers are the
troposphere,
stratosphere,
thermosphere and
exosphere. Each layer has characteristic
temperature gradients. The lowest layer, the troposphere, has a complicated system of clouds and hazes, comprising layers of ammonia,
ammonium hydrosulfide and water. The upper ammonia clouds visible at Jupiter's surface are organized in a dozen
zonal bands parallel to the
equator and are bounded by powerful zonal atmospheric flows (winds) known as
jets. The bands alternate in color: the dark bands are called
belts, while light ones are called
zones. Zones, which are colder than belts, correspond to upwellings, while belts mark descending air. The zones' lighter color is believed to result from ammonia ice; what gives the belts their darker colors is not known with certainty. The Jovian atmosphere shows a wide range of active phenomena, including band instabilities, vortices (
cyclones and
anticyclones), storms and lightning. (
more...)
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Credit: Philipp Salzgeber
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Comet Hale-Bopp sails across the sky in the vicinity of Pazin in Istria, Croatia. To the lower right of the comet the Andromeda Galaxy is also faintly visible. The comet was visible to the naked eye for a record 18 months, twice as long as the Great Comet of 1811. At perihelion, it shone brighter than any star in the sky except Sirius, and its two tails stretched 30-40 degrees across the sky. The passage of Hale-Bopp was notable also for inciting a degree of panic about comets not seen for decades. Rumours that the comet was being followed by an alien spacecraft gained remarkable currency, and inspired a mass suicide among followers of the Heaven's Gate cult.
