3. Mars

Mars is the ruby jewel in our night sky and arguably the hottest travel destination in the Solar System. Thanks to a robot invasion from Earth that began in the 1960's, we probably know more about Mars than every other destination in the Solar System combined. Not bad for a planet so cool that the average summer temperature makes a winter in Antarctica seem positively balmy. It might be freezing, there might be nothing for a human to breathe, but of all planets we know this rocky, red one is the most similar to home. Pack a good spacesuit and plenty of oxygen and ...