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To Margaret Lesser and all the girls in the department

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This book was first published in 1954, and the description of the surface of Venus was in accordance with astronomic beliefs of the period.

Since 1954, however, astronomical knowledge of the inner Solar system has advanced enormously because of the use of radar beams and rockets.

In the late 1950s, the quantity of radio waves received from Venus made it seem that the surface of Venus might be much hotter than had been thought. On August 27, 1962, a rocket probe called "Mariner II" was launched in the direction of Venus. It skimmed by within 21,000 miles of Venus on December 14, 1962. Measuring the radio waves emitted by the planet, it turned out that the surface temperature everywhere was indeed considerably higher than the boiling point of water.

This meant that far from having a worldwide ocean, as described in this book, Venus had no ocean at all. All of Venus's water is in the form of water vapor in its clouds, and the surface is exceedingly hot and is bone-dry. The atmosphere of Venus is, moreover, denser than had been thought and is almost entirely carbon dioxide.

Nor had it been known, in 1954, how long it took Venus to rotate on its axis. In 1964, radar beams bounced off Venus's surface showed that it was turning once in every 243 days (eighteen days longer than its year) and in the "wrong" direction as compared with other planets.

I hope that the readers enjoy this story anyway, but I would not wish them to be misguided into accepting as fact some of the material which was "accurate" in 1954 but which is now outdated.

Isaac Asimov

November, 1970 pqdm.com