In Roman mythology, Mercury was a minor deity whose job it was to act as a fleet-footed messenger to more senior gods. To facilitate this task, his sandals both had little wings attached; he also wore a hat which resembled the hard-hats we see nowadays on building sites, and this hat was similarly, and very usefully, equipped with wings.
But in his spare time Mercury had a wide range of personal portfolios: he was the god of science and commerce, and the patron of travellers, vagabonds and thieves.
When the astronomers of old identified a planet that seemed to move much faster than any other, it seemed to them a good idea to name it after this Flash Harry of the ancient world. The planet Mercury is the closest to the sun, and its apparent speed as it moves through its relatively limited amount of space is greater than that of any of the other planets.
Mercury's proximity to the sun has another obvious consequence: its "year", at 88 Earth days, is the shortest in the solar system. To complicate the issue further, the planet revolves on its axis in a period that is almost exactly two-thirds of its own year, and this has a peculiar effect on the apparent length of Mercury's "day"; as measured from noon to noon by someone standing on the surface of the planet, a "day" on Mercury, at 176 Earth days, would be twice as long as the Mercurian year.
It is a small world, only 3,000 miles in diameter and not much larger than our moon. Moreover Mercury is moonless; like Venus, it is a solitary traveller through cold, dark, almost empty space.
It has virtually no atmosphere, and since there is therefore no greenhouse effect, the parts of the planet exposed to the sun heat very quickly, and temperatures plunge in the shade with quite remarkable speed. The surface temperature during a Mercurian night may drop to -180Celsius and rise during the day to +350 or more.
The range of temperatures experienced is further enhanced by the unusual eccentricity of Mercury's orbit. Instead of describing a near-circle, it sometimes comes as close to the sun as 30 million miles, while at other times it veers away to 40 million miles or more.
And when Mercury is closest to the sun, the temperature on exposed surfaces can rise to over 400C. Then, to add variety, there are shady nooks and crannies near the poles, deep inside some of Mercury's massive craters, where perennial ice exists like smaller, local versions of our Earthly icecaps.