The size of Venus and Earth is roughly the same and millions of years ago Venus possibly had Earth-like oceans. But Venus is now arid and its air up to 100,000 times drier than Earth's.
Chemical hints are the only thing left of oceans on Venus. The strongest clue is atmospheric deuterium, a form of hydrogen found in earthly seas, which remains on Venus like a chalk outline of long-dead bodies of water.
The lack of oxygen and other ions associated with water is mysterious. If Venus once had liquid water, it is possible that its molecules should linger in the atmosphere. The grip of gravity simply not let go, no matter how hot a planet is.
A new study has however showed that the sun is only indirectly a factor. The researchers said that the super-strong electric wind of Venus is the real culprit.
"It's amazing, shocking," NASA's Glyn Collinson, an expert in atmospheric electric fields and an author of the new study, said in a statement. "We never dreamt an electric wind could be so powerful that it can suck oxygen right out of an atmosphere into space." (This electric wind is no gentle spring breeze, but a charged stream similar to solar wind.)
Earth also has an electric field in the atmosphere but it weaker and cannot be measured easily. It was also tough to measure Venus's field, as pointed out by Collinson and his colleagues in the journal Geophysical Research Letters. At about 10 volts, the electric wind of Venus is at least five times stronger than those of Earth.