A Japanese mission, also called the Venus Climate Orbiter, is approaching Venus and will enter orbit on December 7, 2010. Project scientist Takeshi Imamura believes a close-up look at Venus could teach us a lot about our own planet. 

"In so many ways, Venus is similar to Earth. It has about the same mass, is approximately the same distance from the sun, and is made of the same basic materials," says Imamura. "Yet the two worlds ended up so different."

The Venusian surface is hot enough to melt lead. The planet's 96% carbon dioxide atmosphere is thick and steamy with a corrosive mist of sulfuric acid floating through it. The terrain is forbidding, strewn with craters and volcanic calderas – and bone dry.

Although a parade of U.S. and Soviet spacecraft has visited Venus since 1961, no one yet knows how it became Earth's "evil twin." Did it suffer from a case of global warming run amok – or something else? When Akatsuki reaches Venus in December, it will begin to solve some of the mysteries hidden in the thick Venusian atmosphere. By comparing Venus's unique meteorology to Earth's, scientist will learn more about the universal principles of meteorology and improve the climate models used to predict our planet's future.

Particularly puzzling is Venus's "super-rotation."  Fierce, blistering winds propel an atmosphere filled with storms and sulfuric acid clouds in a churning maelstrom around Venus at over 220 miles per hour, 60 times faster than the planet itself rotates.

Image credit:   ESA/MPS, Katlenburg-Lindau, Germany 

Within this swirling cauldron are other Venusian riddles to be solved: What is the origin of the 12-mile thick layer of sulfuric acid clouds that shrouds the planet? And how does Venus' lightning crackle through this strange brew?

Akatsuki, bristling with cameras, will circle the exotic planet's equator in an elliptical orbit for at least 2 years, monitoring the atmosphere at different altitudes using various wavelengths (IR, UV, and visible). With this data and data from the spacecraft's radio dish, scientists will reconstruct a 3D model of the atmosphere's structure and dynamics.

The spacecraft's orbit will match the circulation of Venus's clouds, allowing the instruments to monitor cloud movement from directly above for 20 hours at a time. Scientist will assemble the images to produce a cloud motion time-lapse movie, much like a weather forecaster on television might show you of Earth. The instruments will also scrutinize the planet's surface for volcanic activity that could be contributing to the sulfur contents of the atmosphere. If any active volcanoes are spouting hot lava on Venus, one of the onboard infrared cameras will detect the thermal emission.

In addition, Akatsuki's Lightning and Airglow Camera will hunt for lightning in order to settle a longstanding debate. On Earth, the standard theory of lightning requires water ice particles on which positive or negative charges are induced via collisions. But there are no ice particles in Venus's hot, dry atmosphere--so how does Venusian lightning get started? It may be that charge separation can occur in sulfuric acid clouds--or perhaps some unknown solid particles exist in the atmosphere and play an important role. 

An artist's concept of Akatsuki at Venus. Credit: Akihiro Ikeshita

The European Space Agency's Venus Express is already circling Venus in a polar orbit, performing a global investigation of the Venusian atmosphere and of the plasma environment. This spacecraft is using spectrometers to examine the atmosphere's chemistry. Together, these two spacecraft will yield more information than either spacecraft could produce alone. For example, scientist will be able to trace the circulations of chemicals in Venus's atmosphere that determine its chemical state.