The ISAS expects to start full-fledged preparations for launching the domestic M-5 rocket in fiscal 2002, which starts next April, following endorsement of the plan on May 10.

While Mars has attracted popular attention with speculation about the possibility of life there, only the United States and the former Soviet Union have sent probes to Venus so far.

Although the U.S. and Europe are also planning Venus explorations, Japan's scheme is the only one to focus on the planet's atmosphere, the ISAS sources said.

Venus' atmosphere consists mainly of carbon dioxide and, due to the greenhouse effect, the temperature reaches almost 900 degrees Fahrenheit (470 degrees Celsius).

No surface features on the planet are older than 300 million years and some geographical configurations are believed to be formed by volcanic activity.

The atmosphere rotates in the same direction as the planet, but at a maximum speed 60 times faster. Venus rotates every 243 days.

Venus has an atmosphere 90 times denser than that of Earth and, as a result, the detailed mechanism of its atmosphere, including its rapid air currents, is not well understood.

According to ISAS sources, the probe will be equipped with a camera that uses a special kind of infrared radiation that can penetrate the dense Venusian atmosphere.

The probe will take pictures to help understand the three-dimensional (3-D) structure of the planet's atmosphere and its rapid rotation.

The probe will also check whether there are any active volcanoes.

"Earth may also become a planet like Venus if global warming continues," said project head Koichiro Oyama. "If we find out the process of how Venus evolved, it will be an important key to predict the future of Earth."