During the first half of the 20th century, astronomers occupied themselves with four theories that explained the hidden, cloud-covered surface of the planet Venus.
The first theory proposed that Venus was a vast desert with howling winds that sculpted surface rocks into wild, hoodoo formations.
The second and third theories proposed that Venus was covered by either a vast ocean of seltzer water or bubbling seas of petroleum.
A fourth theory proposed a planetwide swamp similar to Earth's coal-forming Carboniferous wetlands complete with alien dinosaur-like creatures slogging through the muck and mire.
These steamy Venusian theories provided great sci-fi landscapes, but they were dead wrong. The theories were based on scant facts known at the time: Namely, that Venus was cloud covered, Earth sized, and within our solar system's zone of habitability. But how one derives planetwide swamps or oceans from bare bones astronomical data illustrates more the power of human imagination over scientific fact finding.
No matter, it was only after NASA's Mariner II robot flyby of our sister planet in 1962 that these four competing theories were finally discarded.
In truth, Venus is a tad like theory no. 1: it's a blistering, arid landscape crushed at the bottom of an ultra-dense atmosphere of carbon dioxide gas; as a result, its surface temperature is pushed above the melting point of lead solder.
While there's growing evidence suggesting that Venus indeed had oceans of water briefly during its prehistory, it is presently a dessicated planet that's very unlike Earth.
Most striking is Venus' lack of plate tectonics-the means by which carbon compounds are recycled through crustal rocks. Without such a dynamic geo mechanism, Venus has been dubbed the "runaway greenhouse effect" planet. It became the poster child for global warming proponents, thanks to its excessive natural amounts of atmospheric carbon dioxide.