A concise 12,000-word eBook short read about Mercury, which has now regained its place as the Solar System's smallest planet. It is a world of extremes: surface temperatures range from 427 °C, hot enough to melt lead, to a chilly -183°C. Although smaller than some of Jupiter's and Saturn's moons, it is denser than any planet apart from Earth. It is so close to the Sun that the peculiarities of its orbit can only be explained in terms of Einstein's general theory of relativity.
Although brighter than any star, Mercury is so elusive that most of us never see it. Not only it is difficult to observe, it is difficult reach from Earth, and only two space probes have ever visited it - yet Mercury might hold clues about the early history of our Solar System.
