Much ado about Mercury

One of the planets the universe knocked about a bit.

Those clever Babylonians discovered the planet Mercury, which they named Nabu after their god of wisdom and writing. There are references in a Babylonian text compiled by a 14th century BCE Assyrian astronomer.

The ancient Greeks called the planet Hermes and the Romans followed suit, naming it Mercury after the fleet-footed messenger of the gods, because it traverses the sky faster than any other planet.

Mercury was formed about 4.6 billion years ago and was promptly bombarded by meteors and rent by volcanic activity. A mega impact 3.8 billion years ago left a crater 1,550 km in diameter now called the Caloris basin. Discovered in 1974, it is ringed by mountains 2 km high.

Most of Mercury’s craters are named after famous writers, artists, and composers. According to the rules of the International Astronomical Union, new craters must be named after an artist famous for more than fifty years and dead for more than three years.

MercuryMercury is one third the diameter of Earth and the smallest planet in our solar system. The largest – Jupiter – is almost thirty times the diameter of Mercury.

Mercury is the closest planet to the sun, which it orbits in 88 days. Consequently, one Earth year is the equivalent of nearly four on Mercury.

Temperatures on Mercury can reach up to 427 degrees Celsius, yet on the side that faces away from the sun, it can be as cold as minus 173 degrees.

So far only two spacecraft have made it to Mercury. In 1975, Mariner 10 made three flybys, during which it took more than 2,800 photos of the surface. And from 2011 to 2015 NASA’s exploration spacecraft Messenger orbited the planet, discovering both water ice and organic compounds in permanently shadowed craters near the planet’s north pole.

It seems that Mercury has long influenced humans and not just when it happens to cross the face of the sun. The Roman philosopher Cicero was fascinated by astronomy and doubtless knew of it. And he imagined its effect on ancient cave-dwellers who emerged to glimpse the stars for the first time:

“If there were beings who had always lived beneath the earth, in comfortable, well-lit dwellings, decorated with statues and pictures and furnished with all the luxuries enjoyed by persons thought to be supremely happy, and who, though they had never come forth above the ground, had learnt by report and by hearsay of the existence of certain deities and divine powers; and then if at some time the jaws of the earth were opened and they were able to escape from their hidden abode and to come forth into the regions which we inhabit; when they suddenly had sight of the earth and the seas and the sky, and came to know of the vast clouds and mighty winds, and beheld the sun, and realized not only its size and beauty but also its potency in causing the day by shedding light all over the sky, and, after night had darkened the earth, they then saw the whole sky spangled with stars, and the changing phases of the moon’s light, now waxing and now waning, and the risings and settings of all these heavenly bodies and their courses fixed and changeless throughout all eternity – when they saw these things, surely they would think that the gods exist and that these mighty marvels are their handiwork.”

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