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(So named (Latin Mercurius, "Mercury") by the alchemists because of its fluidity) A heavy, silver-white metallic chemical element, the only metal liquid at standard temperature and pressure, which sometimes occurs in a free state but usually in combination with sulfur. Mercury is toxic and cumulative in the body, readily absorbed through the respiratory tract, the gastrointestinal tract or through the skin. It is used in thermometers, barometers, and other laboratory instruments; in mercury switches and other electrical apparatus; in mercury-vapor lamps; and in dentistry.
Symbol: Hg (Latin: hydrargyrum) Atomic number: 80 Atomic weight: 200.59 Density (at room temperature and pressure): 13.546 g/cc Melting point: -38.87°C Boiling point: 357°C Valence: +1, +2 Ground state electron configuration: [Xe]4f145d106s2
The planet Mercury is the closest planet to the Sun in our Solar System. It was named after "Mercury" the speedy Roman god. It was given this name because it appears to move faster than any other planet. Mercury has quite a lot in common with our moon, although it is larger. (Two other moons are actually larger than Mercury, they are Titan and Ganymede). The only planet smaller than Mercury is Pluto.
The surface of Mercury is very similar to that of the moon. It is covered in craters, jagged cliffs, and dusty hills. From Mercury's surface the sun would take up nearly half of the black sky (the sky on Mercury is black, not blue, this is because the planet has almost no atmosphere to generate the illusion of a blue sky). From the nighttime side, both Earth and Venus would be visible about half of the time.
It is difficult to view Mercury from Earth. It can only be seen during the daytime (which is not exactly a great time to attempt to view planets), or for a brief period before the sunrise and after the sunset (this isn't much better, as it appears just over the horizon, and the light is going through a lot more atmosphere than if you were viewing it head on). Most of our information about Mercury comes from the Mariner 10 spacecraft, which flew past Mercury three times in the mid 1970s.
Early astronomers thought that Mercury was tidally locked, and only showed one face towards the Sun (like our own moon). By the early 1960s that theory had been refuted, because researchers determined (via radio waves), that Mercury's dark side was too hot for it to possibly be tidally locked. By 1965 they had determined a rotational period of 59 days, later the Mariner 10 data showed an exact rotational period of 58.646 days. So it is not tidally locked, but its rotation an orbit are related. It has exactly 1.5 days per Mercurian year (in other words it spins around 3 times for every two times it rotates the sun). This peculiar trait means that a "day" on Mercury actually lasts 176 Earth days (even though it only takes 58 days to rotate). There is much evidence to support the theory that Mercury once had a much faster rotational period (as quick as 8 hours), but that the Sun has been slowing it down for millions of years. If this theory is true, then Mercury will eventually become tidally locked.
The Mariner 10 space probe flew past Mercury three times in 1974 and 1975. During these flights we learned quite a bit about the planet, and managed to photograph nearly half of its surface. The biggest surprise was the discovery of a magnetic field. Everyone had thought that Mercury was far too small to support the required core of molten iron to generate a magnetic field via the dynamo effect. This field is a weak one, only 1 percent of the strength of the Earth's magnetic field. A few researchers say that the field actually comes from magnetized iron rocks scattering the planet, and not a molten core at all. One thing we do know for certain is that Mercury is made up mostly of metal. The planet is just as dense as Earth is, and it appears to be made up of at least sixty percent metal (iron mostly).
The surface of Mercury is that of a dead world. It is mostly covered with great plains, left over from prehistoric lava flows. These plains are broken up by great cliffs that run for hundreds of kilometers. These cliffs were apparently created far in the past when Mercury contracted in size (because of a reduction in temperature). Finally there are the craters, they are everywhere. Mercury is as littered with craters as our own moon. Mariner 10 photographed craters from as small as its minimum resolution (100 meters), to as large as 1300 kilometers (the Caloris Basin). These craters are of all different ages, from billions of years old, right up to fresh craters that are only a few thousand years old (virtual youngsters).
Recent data has suggested that Mercury may have a bit of water at its North Pole. Radar data indicates that the interior of several craters (which are in polar areas that are never in direct sunlight), may have frozen water just below the surface. Although further research is needed before this can be considered a fact. But luckily further research is on the way, in the form of the Messenger space probe, which was originally scheduled to visit Mercury on March 23, 2004. The Messenger launch was unfortunately delayed, and it did not end up being launched until August 3, 2004, and the first Mercury flyby is not scheduled until 2008, with actual orbit being scheduled for 2011. The reason it is going to take so long is because NASA set things up so gravity does almost all the work.
Known to the Greeks as Hermes, Mercury was the son of Jupiter and Maia. Worshipped by the Romans from early days (many of the legends of Hermes were 'adopted' from Greece), a temple was dedicated to him on the Aventine Hill in Rome on 15th May, 495 BC, the anniversary of which was celebrated annually, jointly with his mother.
As the Greeks, so with the Romans. He was a god of trickery, deceit and thievery, also of commerce and communication - a strange mix, which made me wonder about the honesty of Roman businesspeople. He was considered to be the messenger of the gods, and is also said to have guided the souls of the dead into Hades, taking the role of a psychopomp.
His role as thief began shortly after his birth, when he stole a herd of cows from Apollo, tricking his pursuers by making shoes for the cows and having them walk backwards to confuse the trail. From the entrails of some of the cows, Mercury made the strings of a lyre, which he later traded with Apollo for the cows he had stolen.
Fleet of foot, he is often pictured wearing either winged sandals (talaria) or a winged cap (a petasus), and he is frequently portrayed carrying a caduceus, a staff of hazel (or willow) entwined with snakes, which served to protect him in his travels. His 'job' as messenger enabled him to move throughout all the worlds, both celestial and earthly, which enabled him to become knowledgeable about many things which were mysteries even to other gods.
He later became identified with the Germanic god Woden (Norse Odin), and indeed, the same weekday was dedicated to him - Wednesday ("Wodin's day") and the Norwegian Onsdag (Odin's Day), also known to the Romans as Dies Mercurii ("Mercury's day") - a reminder of this is still with us, the French for Wednesday being Mercredi.
He was known by many names in different cultures. Hermes, Wodin, Turms to the Etruscans, Thoth to the Egyptians, Nabu to the Assyrians and Gud to the Sumerians.
Major sources: http://www.hermograph.com/science/mercury2.htm Encyclopędia Britannica
