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Mercury

Planet Mercury

 Automatic translationAutomatic translation Category: Planets and dwarf planets
Updated June 01, 2013

Mercury is the closest planet to the Sun and the smallest planet in the solar system. Its size is slightly larger (28%) than our moon craters and surface are very similar. Mercury travels around the Sun faster than any other planet because of its proximity. It is visible from Earth just before sunrise or just after sunset. Mercury never strays more than 27 degrees from the Sun (it is the angle clockwise when it is one hour). Mercury is a mysterious planet that we begin to understand through the Messenger probe. Messenger before, we knew that 45% of its surface in detail. It has no satellite.
Mercury has a very eccentric orbit which changes its radius from 46 to 70 million kilometers. Its name comes from the Roman god Mercury. The proportion of iron Mercury intrigue scientists. Three hypotheses have been proposed to explain the high metal content of Mercury and its core enormous.
1 - Mercury originally had a report metal - silicate similar to that of chondrites and a mass of about 2.25 times the current mass, but in the early history of the solar system, Mercury was struck by a planetesimal of about 1/6 of that mass. The impact would have torn the world a large part of its crust and mantle, leaving only the metal core and a thin coat.
2 - The rate of heavy elements such as iron, present in the solar nebula was larger in the vicinity of the Sun, knowing that these heavy elements were gradually distributed around the Sun (the more you get away, there was less of heavy elements). Mercury, closest to the Sun, would have amassed more material heavier than other planets to form its nucleus.
3 - Mercury may have formed very early, even before the energy released by the Sun has stabilized. Mercury would have been his training twice its current mass, but as the protostar contracted, the temperature around Mercury have been increased to 10000 K. Much of Mercury's surface would have been vaporized, forming an atmosphere of rock vapor, which was then transported elsewhere by the solar wind.

 
Mercury Planet
   
Mean radius 2439.7 km
Diameter 4879.4 km
Mass 3.302×1023 kg
Mean density 5.427 x 103 kg/m3
Aphelion 69 817 079 km
Perihelion 46 001 272 km
Semi-major axis 57 909 100 km
Eccentricity 0.205 630
Rotation period 58.6462 days
Gravity 3.701 m/s2
Escape velocity 4.25 km/s
Inclination axis 0,01°
Average orbital speed 47.87 km/s
Orbital period 87.969 days
Inclination to Ecliptic 7.005°
Temperature min : -183°C
max : 427°C
Mean albedo 0.106


Definition of a planet:
"A planet is a celestial body that is in orbit around the Sun, which has sufficient mass for its gravity to overcome the cohesive forces of the solid body and maintain hydrostatic equilibrium (spherical), which eliminated any body moving in an orbit close." This definition was approved August 24, 2006, during the 26th General Assembly of the IAU (International Astronomical Union) by a show of hands about 400 scientists and astronomers after ten days of discussions.

Nota: Mercury represents 0.0025% of the total mass of the solar system.
 Planet Mercury

Image: This colorful view of Mercury was produced by using images from the color base map imaging campaign during MESSENGER's primary mission. These colors are not what Mercury, but rather the colors enhance the chemical, mineralogical, and physical differences between the rocks that make up Mercury's surface. Image Credit: NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington.

mercury size

Image: Comparative sizes of the terrestrial planets, Mercury left, Venus, Earth and Mars.

Orbit of Mercury

    

Mercury is a planet lower, therefore the space within the orbit Earth-Sun. Thus it has phases like the Moon. Dense and rich in iron, Mercury has virtually no atmosphere. Mercury is easily visible with binoculars or even the naked eye, but it is still very close to the sun, it is difficult to see in a sky lit.
We can observe planets that because they reflect sunlight. A planet is brighter than a star, it shines with a constant brightness among the stars.
Planets twinkle less than stars. Mercury, because of the high percentage of variation of its distance from Earth, shows a strong variation of its apparent size. Mercury for the apparent diameter of the disk varies between 4.8'' and 13.3''.
To identify the planets must familiarize themselves with the stars of the zodiac because they follow the ecliptic. Seen from Earth, Mercury seems to pass during its revolution, is west of the Sun.
Because of the proximity of the Sun, the planet appears low on the horizon at sunrise and sunset.
Mercury has been known since the time Sumerian (3000 BC). She received two names by the Greeks: Apollo for its apparition as a morning star and Hermes as an evening star. However, the Greek astronomers knew it was a single body.

 

Greek Heraclius even believed that Mercury and Venus orbited the Sun, not the Earth.
Mercury's orbit is highly eccentric, the perigee is only 46 million km from the Sun while its aphelion is 70 million miles.
Curiously, it runs its perigee orbit corresponding to a very low speed 47.36 km/s.
19th century astronomers made ​​very detailed observations of Mercury's orbital parameters but could not explain based on Newtonian mechanics.
The small difference between the observed and predicted values ​​constituted a minor problem but disturbing for many decades.
It was suggested that another planet (sometimes called Vulcan) was in an orbit similar to that of Mercury, to explain this difference.
The real answer is given by the theory of General Relativity of Einstein. This was the first great success of general relativity.

 mercury front of the sun

Image: Photo of Mercury which passes the Sun. Among the bodies of the solar system large, only the Moon, Mercury and Venus can pass the Sun to an observer on Earth. If, in the case of the Moon phenomenon (eclipse) is common, it is not the same for Mercury and Venus with the phenomenon of passing before the sun is rare. It is less spectacular than a solar eclipse because the maximum apparent diameter of Mercury is about 1/200th that of the Sun and Venus is about 1/30th.

Day "Mercurian"

    

Until 1962, it was believed that the day "Mercurian" had the same length as its "year", so that Mercury would present the same face to the Sun as does the Moon facing the Earth. But in 1965, this was denied by Doppler radar observations. We now know that Mercury made ​​three rotations on itself in its two years.
Mercury is the only body in the solar system known to have a resonance orbit / rotation ratio other than 1:1.
This resonance and the eccentricity of its orbit would produce a strange sight for a possible observer on the surface of Mercury at certain latitudes, the observer would see the Sun rise and then gradually increase in apparent size as it moves slowly toward the zenith.
At this point the Sun would stop, briefly reverse would, would stop again before resuming its path toward the horizon of decreasing size.

 

During this time, the stars would be moving three times faster across the sky. Observers located in other parts of the movements would Mercury different but equally bizarre. Temperature variations on Mercury are the most extreme in the solar system: 90 K to 700 K.
The surface temperature can reach 450°C during the day but very close to the Sun, down to -200°C overnight. Because Mercury has an axis of rotation substantially perpendicular to the plane of its orbit, sunlight is only glancing at the poles, it is conceivable that funds craters never informed of these regions may contain ice.

Image: Artist Image, day on Mercury, the Sun is 2 times bigger than on Earth.

 Mercurian day, day of Mercury, the Sun is 2 times bigger than on Earth

Surface of Mercury

    

Images of Mercury's surface resemble images of the moon traces of lava flows and craters combine to indicate that Mercury, like the Moon is a dead star for several billion years.
In addition there is virtually no atmosphere which prohibits aqueous erosion and wind. There is however a weak magnetic field.
In many ways, Mercury is very 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 g/cm3 against 3.34). Mercury is the second densest planet in the solar system after Earth.
The density of the Earth is due in part to gravitational compression; otherwise, Mercury would be denser it.
This is explained by the fact that the iron core of Mercury is relatively larger than that of the Earth, probably representing the majority of the planet.

 

As a result, Mercury has a mantle (crust silicates), relatively thin. Mercury has a large iron core with a radius of 1800 to 1900 km.
The envelope of silicates (similar to the crust and mantle terrestrial) is only 500 to 600 km.

Image: False color ranging from visible light to near infrared. The image resolution is 500 meters per pixel.
credit: MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging), NASA.

 ground mercury

Atmosphere of Mercury

    

Mercury has a very thin atmosphere of atoms arising from its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space. The atmosphere of Mercury exosphere or rather, is replenished constantly. Mercury's surface reveals enormous escarpments, some making up to hundreds of kilometers wide and 3000 m high. Some cuts in the rings of craters and other features of the relief of the same kind, show that these cliffs were formed by compression. One of the biggest reliefs of the surface of Mercury, the Caloris Basin has a diameter of about 1300 km. It is known to be similar to the large pool "maria" of the Moon. As the lunar basins, it was probably caused by a massive meteorite impact. In addition to its many craters, Mercury also has relatively flat plains. Some may be the result of volcanic activity and other consequence deposits of ejecta from impact craters. Curiously, radar observations of Mercury's north pole (a region not mapped by Mariner 10) reveals the existence of water ice hidden in the protective shadow of some craters.

 

Mercury has a small magnetic field whose intensity is 1% of that of the Earth. Mercury has no satellite.

Video: The entire surface of the planet Mercury has been mapped by the Messenger probe, which flew for the first time Mercury in 2008 and placed in orbit around it in 2011. Before this date, we only knew half of the surface of Mercury. This video was made ​​from thousands of images of Mercury, processed colors enhanced to, to highlight the different properties of the surface of the closest planet to the Sun. You can admire this small terrestrial planet rotates, the ejecta that radiate from a northern crater, then to the middle of the video the Caloris basin, antique lava filled impact basin. Image Credit: NASA / JHU Applied Physics Lab / Carnegie Inst. Washington.

 

After Mariner 10, Messenger

    

The first spacecraft to have visited Mercury was Mariner 10 sent on 3 November 1973 by NASA to study Venus. NASA decides to modify the program to fly by Mercury Mariner 10 flybys and 3 were carried out in 1974 and 1975. After 3500 pictures of the sunny side of Mercury, the spacecraft failed fuel and the mission was stopped. Messenger probe took the baton and Mercury flew on 14 January 2008.
Its objective is the study of the surface of Mercury to answer a number of questions about its density, its atmosphere, its geological history, the structure of its core, its huge cloud of sodium, its magnetic field ... Messenger was launched August 2, 2004 at 6:16 UTC from Cape Canaveral by the Boeing Delta II launcher. Messenger probe used the gravity fields of the Earth and Venus which accelerated with each pass over the planets to reach Mercury in January 2008.
Three flybys of the planet at an altitude of about 200 kilometers before it needs to go into orbit around Mercury on March 18, 2011.
Then it photographed areas plunged into darkness flybys of Mariner 10. On Mercury, the surface temperature can reach over 400 ° Celsius and down at night to -170 ° Celsius.

 

Messenger designed to withstand temperature variations is huge with a large sun shield and covered with a protective ceramic. Some areas of the planet closest to the Sun were unknown until October 6, 2008, when the spacecraft Messenger came graze Mercury for the second time.
The spacecraft MESSENGER (Mercury Surface, Space Environment, Geochemistry and Ranging), flew over Mercury September 29, 2009.
The probe went into orbit around Mercury in 2011 to observe the polar regions, only unknown areas of the planet.

Image: The image shows an impact basin double ring approximately 290 kilometers wide. "This double ring basin, seen in detail for the first time, is remarkably well preserved," notes Brett Denevi, a member of the imaging team for probe and a researcher at Arizona State University in Tempe. Credit NASA.

 Messenger Mercury's surface

Caloris Basin of Mercury

    

The Caloris basin was formed by an asteroid impact or comet during the heavy bombing that took place during the first billion years of the history of the Solar System.
Period of volcanic activity that followed, has produced lava flows that filled the interior of the basin.
Color accentuated the image below reveals these against the volcanic conduits along the banks of the Caloris basin, one of the largest impact basins in the Solar System. This colorful image of the Caloris basin and adjacent regions shows orange shades in the Caloris basin, which indicate these locations volcanic.
Scientists have many questions about the magnetosphere and the nature of the core of Mercury (liquid or solid), the possible presence of ice at the bottom of craters constantly in the shade of the formation of solar system, anomalies in its orbit and evolution in general a planet near the star.
In this program named BepiColombo is being developed by the European Space Agency.

 

Image: against the giant Caloris Basin of Mercury photographed by Messenger spacecraft flew NASA Mercury January 14, 2008. Credit: NASA Messenger (Mercury Surface, Space ENvironment, Geochemistry, and Ranging).

 Caloris Basin of Mercury

Rembrandt impact basin on Mercury

    

The Rembrandt impact basin was recently discovered on images taken by the Messenger spacecraft during the flyby of Mercury in October 2008.
Analyzes show that the basin was formed there about 3.9 billion years ago, at the end of a period of heavy bombardment in the solar system.
The information gathered by instruments Messenger confirmed that magnesium is an important component of materials that form the surface of the planet.
Why parts of the crater 720 km in diameter, they contain much iron?
Pictures of the floor of the crater, indicate reflections from areas containing significant amounts of high iron and titanium. The presence of these elements show that these materials have not been covered by lava flows latest date and perhaps the formation of Mercury. Moreover, the data collected on the surface of Rembrandt are now interpreted as being indicative of a former volcanic past, having relatively active tectonic movements resulting surface.
A careful examination of the image reveals a series of rings located inside the Rembrandt impact basin, as traces of lava.

 

The Rembrandt impact fractured crust of Mercury, and helped to volcanic lava flows to flow inside. Inside the Rembrandt basin can also be observed cliffs and small volcanic craters. In addition, researchers believe that they are on Mercury repeated volcanic eruptions which have formed the crust, much like on Mars.

Crater Rembrandt 
  
Latitude -33.2°
Longitude 271.8°
Diameter 720 KM

Image: High resolution image Rembrandt basin taken by Messenger flew over Mercury in September 2009 and finally into orbit in 2011. credit & Copyright: NASA/JHU APS/ASU/CIW.

 Rembrandt impact basin on Mercury

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