What makes Venus so bright? Huge clouds, 20 miles thick, completely surround it and reflect 75% of the light from the sun that strike them.

　　For a long time, these clouds caused Venus to be a great mystery (谜）to the world's astronomers. If, like other clouds, the ones on Venus were made up of water vapors (水汽），could there not be life hiding beneath them on the planet? Were there “Venusians (金星人)” waiting to communicate with us on Earth?

　　It was an exciting thought, but on that the Mariner recently landed to rest. The Mariner thoroughly examined Venus and its atmosphere, only to find that the cloud cover was made mostly of deadly carbon dioxide (二氧化碳）gas. The atmospheric pressure was 15 to 22 times greater than on Earth, which further disproved the theory of life on Venus.

　　And what did the Mariner find under the clouds? A world of great mountains and smooth areas, dry as a bone. The temperature is about 900°F. That's hot.

　　Although the greatest mystery has been solved, there are still others waiting for us on Venus. Why does Venus rotate (自转）so slowly? What is the inside of Venus like? And most important of all, why is there no water on Venus? If, as it was thought, it was formed about the same time as our planet, it should have water.

　　These questions and others may some day be answered. Until then, Venus will continue to be the brightest mystery in the sky.

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