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VISIBLE TO THE NAKED EYE AROUND SUNRISE AND SUNSET, MERCURY WAS WELL KNOWN IN ANCIENT TIMES. IT IS THE FASTEST-MOVING OF ALL THE PLANETS AND WAS NAMED AFTER THE WINGED MESSENGER OF ROMAN MYTHOLOGY. Mercury is so small and distant—and circles so close to the Sun— that it is difficult to see from Earth. Consequently, very little was known about the planet until comparatively recently. Although Mercury was first observed through a telescope by Italian scientist Galileo Galilei in the early 17th century, it was not until the late 20th century that telescopes with sufficient power to resolve surface details were developed. The big breakthrough in understanding the Sun’s closest neighbor came when spacecraft began to beam back close-ups from the planet. The first was Mariner 10, which made flybys in 1974 and 1975. This was followed, after a gap of more than 30 years, by the MESSENGER spacecraft, which remains in orbit today. Babylon tablets The earliest known record of the observation o
