Tuesday, February 26, 2008

Venus Revealed: Probe Discovers Extraordinary Weather System of the Morning Star

Venus_hemi_left Slowly but surely scientists are unraveling an incredible picture of our Solar System with each planet vastly differing from the next, but all featuring it’s own unique and mysterious beauty. The tan highland area in the center of the image left is called Aphrodite Terra, while the faint green circle to the lower right is a deep canyon named Artemis Chasma.

Named after the Roman goddess of love and beauty, Venus is also known as the “morning star” and “evening star” since it is visible at dawn and dusk to the naked eye, appearing as a bright, white disk from Earth. However, closer up, the planet’s cloudy atmosphere creates a process similar to “urban smog over cities.”

Venus is often called Earth's twin as the two planets are close in size, but that's where the similarity ends. The massive clouds that cover Venus create a greenhouse effect that keeps the planet at a sizzling 864°F. Now Venus Express has revealed our “twin” planet to be extraordinarily fast changing 'global weather' on an extremely large scale. Bright hazes can appear in a matter of days that reach from the south pole to the low southern latitudes and then quickly disappear. Venus’ bizarre weather patterns—unlike anything on Earth—has given scientists new mysteries to solve.

At visable wavelengths of light, the cloudy planet appears serene. All of that changes, however, when scientists switch to the ultraviolet, which reveals an exciting, and mysterious dynamic nature. Ever-changing stripes mark the planet, indicating regions where solar ultraviolet radiation is either absorbed or reflected, respectively.

Venus Express has seen some amazing things while monitoring the behavior of the planet’s atmosphere with its Venus Monitoring Camera (VMC). VMC has captured a series of images showing the development of the bright southern haze. Within days, the high-altitude veil continually brightened and dimmed, moving towards equatorial latitudes and back towards the pole again.

Such global weather suggests that unknown dynamical, chemical and microphysical processes are fast at work on the planet. During these episodes, the brightness of the southern polar latitudes increased by about a third and faded just as quickly.

“This bright haze layer is made of sulphuric acid,” says Dmitri Titov, at the Max Planck Institute for Solar System Research in Germany. That composition suggests the existence of a formation process.

At 70 km and below, Venus’s carbon dioxide-rich atmosphere contains small amounts of water vapor and gaseous sulphur dioxide. normally buried in the cloud layer that blocks our view of the surface.

However, as atmospheric process lifts these molecules high up above the cloud tops, they are exposed to solar ultraviolet radiation. This breaks the molecules, making them highly reactive. The fragments find each other and combine quickly to form sulphuric acid particles, creating the think haze.

“The process is a bit similar to what happens with urban smog over cities,” says Titov.

What causes the water vapour and sulphur dioxide to well up in the first place? The team does not know yet. Titov says that it is likely some kind of internal dynamical process in the planet’s atmosphere, but the influence of solar activity has not been ruled out.

The dark markings, especially, remain one of the biggest mysteries of Venus’s atmosphere. They are caused by some kind of chemical species, absorbing solar ultraviolet radiation. However, planetary scientists do not yet know the identity of the chemical involved, but are eager to unlock the mystery as they continue to probe the mysteries of the “morning star”.

Original here

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