Description The Planet Mercury, number 1 in a set of 9 prints featuring the planets of our Solar System. Mercury is the first planet from the sun and smallest planet in the Milky Way Solar System. Mercury orbits the Sun once every 87.969 Earth days. Surface temperatures range from about 90 to 700 K (183 C to 427 C). The English name for the planet comes from the Romans, who named it after the Roman god Mercury. The earliest known recorded observations of Mercury are from the Mul.Apin tablets. These observations were most likely made by an Assyrian astronomer around the 14th century BC.