Since Venus is closer to Earth than Mars -- both in size and distance -- it would be a much more convenient candidate for manned exploration. There's just a slight hitch: the average temperature is 850 degrees F, and the atmosphere is 90 times denser than ours. In other words, you'd die in the opposite way that Quaid nearly did in Total Recall. Probes have been sent to the planet's surface, but the Russian Venera 13 survived the longest at just 127 minutes in 1982. As it does, NASA has figured a way around all that. In IEEE Spectrum, it outlined a study called HAVOC to build a floating "city" of astronaut-manned zeppelins that would hover 30 miles above the planet.