Even before the Magellan spacecraft saw through Venus’s cloud cover, astronomers were confident that Venus had no water. The surface of Venus is very hot, at least 450 degrees Celsius. It’s hotter than Mercury, which you might expect to be hotter than Venus because it’s closer to the Sun. Mercury, however, has no insulating atmosphere.
The Carbon dioxide in Venus’ atmosphere traps the sun’s heat. This is similar to how a greenhouse preserves the sun’s heat to allow plants to grow. The sun’s rays can pass through the clouds to reach the surface of Venus, but its heat cannot escape. Astronomers knew that water could not exist as a liquid in such hot conditions. However, two nearby planets, Earth and Mars, have water or ice. Did Venus once have water?
Photos from the Magellan spacecraft provide no evidence that water ever existed. The surface of Venus is lined with long river lines, some hundreds of kilometers long. But these lines seem to be caused by lava, not water.
There are no signs of an ancient ocean, or mountains washed away by water. One astronomer says Venus is too hot, Mercury is too cold, and Earth is just right for water.