Mercury (mythology)

In Roman mythology, Mercury (associated with the Greek deity Hermes) (pronounced /ˈmɝkjəri/, Latin: Mercurius listen (help·info)) was a messenger, ^[1] and a god of trade, profit and commerce, the son of Maia Maiestas and Jupiter. His name is related to the Latin word merx ("merchandise"; compare merchant, commerce, etc.). In his earliest forms, he appears to have been related to the Etruscan deity Turms, but most of his characteristics and mythology were borrowed from the analogous Greek deity, Hermes.

Mercury has influenced the name of a number of things in a variety of scientific fields, such as the planet Mercury, and the element mercury. The word mercurial is commonly used to refer to something or someone erratic, volatile or unstable. The term comes from astrology and describes the expected behavior of someone who has the planet Mercury passing through their astrological sign.

Worship

Mercury did not appear among the numinous di indigetes of early Roman religion. Rather, he subsumed the earlier Dei Lucrii as Roman religion was syncretized with Greek religion during the time of the Roman Republic, starting around the 4th century BC. From the beginning, Mercury had essentially the same aspects as Hermes, wearing winged shoes talaria and a winged petasos, and carrying the caduceus, a herald's staff with two entwined snakes that was Apollo's gift to Hermes. He was often accompanied by a cockerel, herald of the new day, a ram or goat, symbolizing fertility, and a tortoise, referring to Mercury's legendary invention of the lyre from a tortoise shell. Like Hermes, he was also a messenger of the gods and a god of trade, particularly of the grain trade. Mercury was also considered a god of abundance and commercial success, particularly in Gaul. He was also, like Hermes, the Romans' psychopomp, leading newly-deceased souls to the afterlife. Additionally, Ovid wrote that Mercury carried Morpheus' dreams from the valley of Somnus to sleeping humans.^[2]

Circus Maximus, between the Aventine and Palatine hills, was built in 495 BC. This was a fitting place to worship a swift god of trade and travel, since it was a major center of commerce as well as a racetrack. Since it stood between the plebeian stronghold on the Aventine and the patrician center on the Palatine, it also emphasized the role of Mercury as a mediator.

Because Mercury was not one of the early deities surviving from the Roman Kingdom, he was not assigned a flamen ("priest"), but he did have a major festival on May 15, the Mercuralia. During the Mercuralia, merchants sprinkled water from his sacred well near the Porta Capena on their heads.

Syncretism

A three-headed image of a Celtic deity interpreted as Mercury and now believed to represent Lugus.

When they described the gods of Celtic and Germanic tribes, rather than considering them separate deities, the Romans interpreted them as local manifestations or aspects of their own gods, a cultural trait called the interpretatio Romana. Mercury in particular was reported as becoming extremely popular among the nations the Roman Empire conquered; Julius Caesar wrote of Mercury being the most popular god in Britain and Gaul, regarded as the inventor of all the arts. This is probably because in the Roman syncretism, Mercury was equated with the Celtic god Lugus, and in this aspect was commonly accompanied by the Celtic goddess Rosmerta. Although Lugus may originally have been a deity of light or the sun (though this is disputed), similar to the Roman Apollo, his importance as a god of trade and commerce made him more comparable to Mercury, and Apollo was instead equated with the Celtic deity Belenus.^[2]

Mercury was also strongly associated with the Germanic god Wotan; 1st-century Roman writer Tacitus identifies the two as being the same, and describes him as the chief god of the Germanic peoples. Julius Caesar, in a section of his "Gallic Wars" describing the customs of the German tribes, wrote "The Germans most worship Mercury," apparently identifiyng Wotan with Mercury.

In Celtic areas, Mercury was sometimes portrayed with three heads or faces, and at Tongeren, Belgium, a statuette of Mercury with three phalli was found, with the extra two protruding from his head and replacing his nose; this was probably because the number 3 was considered magical, making such statues good luck and fertility charms. The Romans also made widespread use of small statues of Mercury, probably drawing from the ancient Greek tradition of hermae markers.

marcury

Mercury

MESSENGER false color image of Mercury
Designations
Adjective	Mercurian, Mercurial[1]
Orbital characteristics[2]
Epoch J2000
Aphelion	69,816,900 km 0.466 697 AU
Perihelion	46,001,200 km 0.307 499 AU
Semi-major axis	57,909,100 km 0.387 098 AU
Eccentricity	0.205 630[3]
Orbital period	87.969 1 d (0.240 846 a)
Synodic period	115.88 d[3]
Average orbital speed	47.87 km/s[3]
Mean anomaly	174.796°
Inclination	7.005° 3.38° to Sun’s equator
Longitude of ascending node	48.331°
Argument of perihelion	29.124°
Satellites	None
Physical characteristics
Mean radius	2,439.7 ± 1.0 km[4][5] 0.3829 Earths
Flattening	< id="cite_ref-Seidelmann2007_4-1" class="reference">[5]
Surface area	7.48×107 km² 0.108 Earths[4]
Volume	6.083×1010 km³ 0.054 Earths[4]
Mass	3.3022×1023 kg 0.055 Earths[4]
Mean density	5.427 g/cm³[4]
Equatorial surface gravity	3.7 m/s² 0.38 g[4]
Escape velocity	4.25 km/s[4]
Sidereal rotation period	58.646 day 1407.5 h[4]
Equatorial rotation velocity	10.892 km/h (3.026 m/s)
Axial tilt	2.11′ ± 0.1′[6]
North pole right ascension	18 h 44 min 2 s 281.01°[3]
North pole declination	61.45°[3]
Albedo	0.119 (bond) 0.106 (geom.)[3]
Surface temp. 0°N, 0°W 85°N, 0°W	min mean max 100 K 340 K 700 K 80 K 200 K 380 K
Apparent magnitude	up to −1.9[3]
Angular diameter	4.5" – 13"[3]
Atmosphere
Surface pressure	trace
Composition	42% Molecular oxygen 29.0% sodium 22.0% hydrogen 6.0% helium 0.5% potassium Trace amounts of argon, nitrogen, carbon dioxide, water vapor, xenon, krypton, & neon

MARCURY

In Roman mythology Mercury is the god of commerce, travel and thievery, the Roman counterpart of the Greek god Hermes, the messenger of the Gods. The planet probably received this name because it moves so quickly across the sky.

Mercury has been known since at least the time of the Sumerians (3rd millennium BC). It was sometimes given separate names for its apparitions as a morning star and as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Heraclitus even believed that Mercury and Venus orbit the Sun, not the Earth.

Since it is closer to the Sun than the Earth, the illumination of Mercury's disk varies when viewed with a telescope from our perspective. Galileo's telescope was too small to see Mercury's phases but he did see the phases of Venus.

Mercury has been now been visited by two spacecraft, Mariner 10 and MESSENGER. Marriner 10 flew by three times in 1974 and 1975. Only 45% of the surface was mapped (and, unfortunately, it is too close to the Sun to be safely imaged by HST). MESSENGER was launched by NASA in 2004 and will orbit Mercury starting in 2011 after several flybys. Its first flyby in Jan 2008 provided new high quality images of some of the terrain not seen by Marriner 10.

Mercury's orbit is highly eccentric; at perihelion it is only 46 million km from the Sun but at aphelion it is 70 million. The position of the perihelion precesses around the Sun at a very slow rate. 19th century astronomers made very careful observations of Mercury's orbital parameters but could not adequately explain them using Newtonian mechanics. The tiny differences between the observed and predicted values were a minor but nagging problem for many decades. It was thought that another planet (sometimes called Vulcan) slightly closer to the Sun than Mercury might account for the discrepancy. But despite much effort, no such planet was found. The real answer turned out to be much more dramatic: Einstein's General Theory of Relativity! Its correct prediction of the motions of Mercury was an important factor in the early acceptance of the theory.

Until 1962 it was thought that Mercury's "day" was the same length as its "year" so as to keep that same face to the Sun much as the Moon does to the Earth. But this was shown to be false in 1965 by doppler radar observations. It is now known that Mercury rotates three times in two of its years. Mercury is the only body in the solar system known to have an orbital/rotational resonance with a ratio other than 1:1 (though many have no resonances at all).

This fact and the high eccentricity of Mercury's orbit would produce very strange effects for an observer on Mercury's surface. At some longitudes the observer would see the Sun rise and then gradually increase in apparent size as it slowly moved toward the zenith. At that point the Sun would stop, briefly reverse course, and stop again before resuming its path toward the horizon and decreasing in apparent size. All the while the stars would be moving three times faster across the sky. Observers at other points on Mercury's surface would see different but equally bizarre motions.

Temperature variations on Mercury are the most extreme in the solar system ranging from 90 K to 700 K. The temperature on Venus is slightly hotter but very stable.

Mercury craters

Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; it has no plate tectonics. On the other hand, Mercury is much denser than the Moon (5.43 gm/cm3 vs 3.34). Mercury is the second densest major body in the solar system, after Earth. Actually Earth's density is due in part to gravitational compression; if not for this, Mercury would be denser than Earth. This indicates that Mercury's dense iron core is relatively larger than Earth's, probably comprising the majority of the planet. Mercury therefore has only a relatively thin silicate mantle and crust.

Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km. The silicate outer shell (analogous to Earth's mantle and crust) is only 500 to 600 km thick. At least some of the core is probably molten.

Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. Thus in contrast to the Earth and Venus whose atmospheres are stable, Mercury's atmosphere is constantly being replenished.

Southwest Mercury

The surface of Mercury exhibits enormous escarpments, some up to hundreds of kilometers in length and as much as three kilometers high. Some cut thru the rings of craters and other features in such a way as to indicate that they were formed by compression. It is estimated that the surface area of Mercury shrank by about 0.1% (or a decrease of about 1 km in the planet's radius).

Caloris Basin

One of the largest features on Mercury's surface is the Caloris Basin (right); it is about 1300 km in diameter. It is thought to be similar to the large basins (maria) on the Moon. Like the lunar basins, it was probably caused by a very large impact early in the history of the solar system.

Weird terrain opposite Caloris Basin

That impact was probably also responsible for the odd terrain on the exact opposite side of the planet (left).

In addition to the heavily cratered terrain, Mercury also has regions of relatively smooth plains. Some may be the result of ancient volcanic activity but some may be the result of the deposition of ejecta from cratering impacts.

A reanalysis of the Mariner data provides some preliminary evidence of recent volcanism on Mercury. But more data will be needed for confirmation.

Amazingly, radar observations of Mercury's north pole (a region not mapped by Mariner 10) show evidence of water ice in the protected shadows of some craters.

Mercury has a small magnetic field whose strength is about 1% of Earth's.

Mercury has no known satellites.

Mercury is often visible with binoculars or even the unaided eye, but it is always very near the Sun and difficult to see in the twilight sky. There are several Web sites that show the current position of Mercury (and the other planets) in the sky. More detailed and customized charts can be created with a planetarium program.