Mercury

Mercury is the planet the closest to the sun and the smallest planet in the solar system. Its size is about identical to our moon and their craters of surface have really very in common.
Mercury travels around the sun more quickly than any other planet. She can only see itself of the earth just before the sunrise or just after the sunset.
Mercury never deviates from more than 27 degrees of the Sun (it is the angle of the needles of a watch when it is one o'clock).
Mercury is a mysterious planet that is beginning to understand through the Messenger probe. Before Messenger, only 45 percent of its surface had been seen in detail.
It possesses no satellite.
Mercury has a very eccentric orbit which makes vary its beam from 46 to 70 million kilometers. Its name comes from the Roman god Mercury Mercury (Roman) / Hermes ( Greek) is the god of the Business, journeys and the messenger of the other gods in the Ancient Rome and the empire Roman. His traditional attributes are the scholarship, mostly held the hand, the winged Pégase or not, the caduceus, the winged sandals as well as the cock and\or the billy goat.. The iron important proportion of Mercury intrigues the scientists. Three hypotheses were proposed to explain the high content in metal of Mercury and its gigantic nucleus.
- Mercury had originally a report metal-silicate similar to that of the chondrites and a mass about 2,25 times the current mass. Early in the history of the solar system, Mercury would have been struck by a small planet about 1/6 of this mass.
The impact would have extracted from the planet a big part of its crust and its coat, leaving only the metal nucleus and the slender coat.

- The rate of heavy elements, as the iron, present in the solar nebula was more important for the neighborhood of the Sun, even that these heavy elements were gradually distributed around the Sun (the more we went away from it, the less there was of heavy elements). Mercury, close to the Sun, would thus have amassed more heavy materials than the other planets to form its nucleus.
- Mercury would have been able to form very early, even before the energy loosened by the Sun stabilizes. Mercury would have had in its formation the double of its current mass, but as the primal star contracted, the temperature near Mercury increased and would have been able to reach 10 000 K.
A big part of the surface of Mercury would have been vaporized, forming an atmosphere of rocky vapors, which would then have been transported somewhere else by the solar winds.

Size comparison of terrestrial planets (left to right): Mercury, Venus, Earth, and Mars.

Mercury is a lower planet, thus included in the space of the orbit Earth Sun. Of this fact it presents phases as the Moon. Dense and rich iron, Mercury practically has no atmosphere. Mercury is easily visible with binoculars or even in the bare eye, but as it is always very close to the sun, it is difficult to see it in a enlightened sky. There are numerous Web sites which show the current position of Mercury (and the other planets) in the sky. We can observe the planets that because of the solar light which they reflect. Mercury, because of the strong percentage of variation of its distance with the Earth, presents a strong variation of its visible size.
For Mercury the visible diameter of the disk varies between 4,8" and 13,3".
A planet is more brilliant, it shines with a constant brightness among stars.

Planets sparkle less than stars. To identify planets it is necessary to get acquainted with the stars of the zodiac because they follow the ecliptic. Seen by the earth, Mercury seems to pass, during its revolution, east on the West of the Sun.
Because of the nearness of the Sun, the planet seems low on the horizon in the rise and in the sunset.
Mercury is known since the period Sumerian (3000 years before J.C.). It received 2 names by Greek: Apollo for its appearance as morning star and Hermes as evening star. However, the Greek astronomers knew that it was about the one and only body. Greek Heraclius even believed that Mercury and Venus orbited around the Sun, but not the Earth.

The orbit of Mercury is strongly eccentric; its perigee places it in only 46 million km of the Sun while its aphelia is 70 million km. Curiously, it crosses its orbit corresponding to its perigee in a very weak speed. The astronomers of the 19th century made very precise observations of the parameters orbital of Mercury but were able to explain them by basing itself on the mechanics Newtonians.
The small difference between the observed values and those predicted constituted a minor but disturbing problem during of numerous decades.
It was suggested that another planet (sometimes called Red admiral) was able to exist in an orbit close to that of Mercury to explain this difference.
The true answer is given by the theory onto the General Relativity of Einstein.

The exactness of its prediction of the movement of Mercury was moreover a factor very important for the credibility of this theory.

Photo of Mercury passing in front of the Sun Among the bodies of the solar system large, only the Moon, Mercury and Venus can pass before the sun for an observer on earth. If, in the case of the phenomenon moon (solar eclipse) is common, it is not the same for Mercury and Venus with the phenomenon of passing before the sun is scarce. It is less than spectacular solar eclipse because the maximum apparent diameter of Mercury is about 1/200ème of the Sun and Venus is about 1/30th.

Until 1962, we believed that the day "Mercurial" had the same duration as its "year", so that Mercury had to present the same in front of Sun as the fact the Moon in front of the Earth. But in 1965, this was contradicted thanks to radar observations Doppler. We know from now on that Mercury makes 3 rotations on itself there 2 of its years.
Mercury is the only body in the solar system known to have an echo orbit / rotation of a ratio other than 1:1. This echo and the eccentricity of its orbit would produce a strange spectacle for a possible observer on the surface of Mercury: in certain latitudes, the observer would see the Sun getting up then gradually increasing in visible size while he moves slowly towards the top.
 

So the Sun would stop, would briefly backtrack, would stop again before taking back its road towards the horizon by decreasing in size.
During all this time, stars would move 3 times as fast in the sky. Observers situated in the other places of Mercury would see different but so bizarre movements.
The temperature variations on Mercury are the most extreme of all the solar system: 90 K in 700 K.
The temperature on Venus is slightly warmer but more very stable.

Flash animation of the day on Mercury.

The images of the surface of Mercury look like the images of the moon; lava flows and varied craters of dimension harmonize to indicate us that Mercury as the Moon is a celestial body died since several billion years. Furthermore there is no atmosphere what forbids any aqueous and wind erosion.
There is however a weak magnetic field. By many aspects, Mercury is very similar to the Moon: its surface is covered with craters very former and it has no tectonic plate.
On the other hand, Mercury is denser than the Moon (5,43 gm / cm3 against 3,34).
Mercury is the densest 2nd planet in the solar system after the Earth. The density of the Earth is partially due to the gravitational compression; or, Mercury would be denser than it. This explains by the fact that the iron nucleus of Mercury is relatively bigger than that of the Earth, representing probably the majority of the planet.

As a consequence, Mercury has a coat / crust of relatively fine silicates. Mercury has a big iron nucleus of a beam of 1800 in 1900 km.
The envelope of silicates (similar to the coat and in earth's crusts) is only from 500 to 600 km.

Image by spreading false colors of light visible to the near infrared. Image resolution is 500 meters per pixel.
credit: MESSENGER, NASA,

Mercury has a very fine atmosphere of atoms lifted by its surface by the solar wind. As Mercury is very warm, these atoms quickly escape in the space. The atmosphere of Mercury is permanently reconstituted. The surface of Mercury reveals enormous steep slopes, some making up to hundreds kilometers wide on 3000 m of height. Certain cuts in the rings of craters and other peculiarities of the relief of the same kind, show that these steep slopes were formed by compression.

One of the biggest reliefs of the surface of Mercury, the basin Calorisin is one diameter of about 1300 km. It is known to be similar to the big basin (Maria) de la Lune). As for the lunar ponds, it was credibly caused by an enormous impact of meteorite. Besides its numerous craters, Mercury also has relatively flat plains. Some people could be the result of a volcanic activity and the others the consequence of a deposit of ejected stemming from craters of impact.

Curiously, radar observations of the North Pole of Mercury (a region not mapped to Marinade 10) reveal the existence of ice-cold water hidden in the shadow defender of certain craters.
Mercury has a small magnetic field the intensity of which represents 1 % of that of the Earth... Mercury has no known satellite.

Mercury

Mars

Uranus

Venus

Jupiter

Neptune

Terre