1 Ishmael: A Martian robot. Well well.
1 SFX: Knock! Knock!
1 Ishmael: Excuse me.
2 Man in Black: There's no such thing as Martian robots.
3 Ishmael: You're a bit late.
4 Man in Black: There's no such thing as me being late. You probably just saw the planet Venus.

Ah, Venus. For much the same reasons that our knowledge of Mars has increased explosively in the last 50 years, the same has happened for Venus.

Up until the 1960s, Venus was basically a complete mystery. We knew it was a planet almost the same size as Earth, and it had an atmosphere, and it had bright clouds in that atmosphere, but apart from that we knew virtually nothing. Because of the obscuring clouds, we couldn't see anything on its surface, and we didn't even know how fast the planet rotated.

Let's see. A planet roughly Earth sized, with atmosphere and lots of clouds, somewhat closer to the sun. Logically that means it's warm, and the clouds tell us it's wet. So it's probably covered with hot, steamy jungles. A sort of primitive world. Heck, there are probably dinosaurs there!

That's how popular thinking went in the first half of the 20th century. The scientific community wasn't so drawn to populating the planet with jungles and dinosaurs, but agreed that it must be warm and wet. Spectral signals from the atmosphere indicated a high concentration of carbon dioxide. This would dissolve into an equilibrium state with the oceans of water, creating oceans of carbonated water. What an exotic and exciting thought! In the not-too-distant future we could take interplanetary holidays in this tropical paradise and swim in oceans of fizzy water.

It wasn't until 1962 that we got our first inkling of what Venus was really like. As part of the space race, the US and Soviet Union competed to be the first to send probes to our sister planet. The American Mariner 2 probe was the first success (after the failed Soviet Venera 1). From a fly-by of the planet, Mariner 2 returned microwave radiometer scan data indicating that parts of the atmosphere had a temperature of around 500 K (230°C or 450°F). This implied that the surface might be even hotter.

The next big success came with the Venera 4 lander in 1967. The landing capsule was designed to float, in case it happened to land in an ocean of soda water. The descent parachute was temperature proofed to 450°C, and the capsule was made to withstand pressures of up to around 100 atmospheres. None of this helped. After reporting that the atmosphere of Venus was 95% carbon dioxide, with virtually no trace of water at all, and with temperature climbing above what Mariner 2 had reported, and the atmospheric pressure a crushing 22 atmospheres and still rising, Venera 4 stopped transmitting.

This was something of a shock. The Soviets realised a Venus probe would not be landing in water, so didn't bother designing future probes to float. In 1970, Venera 7 finally became the first probe to land on another planet. It reported the temperature on the surface was a staggering 460°C (860°F), and the pressure over 90 atmospheres. The brave probe lasted 23 minutes before these hellish conditions destroyed it.

The clouds? Those beautiful white clouds that make Venus so alluring? They turned out to be made of sulphuric acid, not water.

And so, in the course of a few years of astonishing scientific discovery, Venus went from a welcoming tropical paradise of dinosaurs and fizzy oceans to one of the nastiest places imaginable in the entire solar system. But that makes it even more fascinating, because now it's something we know about. Venus is a place, a destination, not merely a dream in our minds.