General information about Mercury

Mercury, the closest to the Sun, a large planet in the solar system and the smallest of the terrestrial planets has no moons. Telescopic observations of Mercury with Earth is extremely difficult, partly because of its small size and partly due to the fact that on the celestial sphere, he does not depart from the sun for more than 28 °, since its orbit lies far inside the orbit of the Earth. For the same reason, the disc of Mercury (like Venus, another planet bottom) shows the cycle of phases like the phases of the moon. Prior to overflights, "Mariner 10 in 1974 and 1975 he on the surface of Mercury and the details about the planet itself was known to very few. Mariner 10 was launched into such an orbit around the Sun, which before had been spent for the necessary positional control of fuel supplies, he met with Mercury three times and passed over 10000 images with better resolution of 100m. Sent to Earth image provided a map covering about 35% of Mercury's surface. This is the only spacecraft has studied directly Mercury. At the March 2004 planned start-up to the side of Mercury American interplanetary probe "MESSENGER" (MErcury Surface, Space ENvironment, GEochemistry, and Ranging - the study of Mercury's surface, the surrounding space, structure and geochemical mapping).

"MESSENGER" will be the first terrestrial device that will explore the nearest to the Sun, the planet from orbit an artificial satellite. Flight schedule of the probe provides two flights by Mercury (in 2007 and 2008) and the yield on its orbit in 2009. He then within a year will pass to the Earth science information, and then life with him will be extended if the state allows onboard equipment.

Motion features

Photo mosaic of the Southern hemisphere of Mercury, made with the Mariner 10 during the second flight near Mercury 21 September 1974 to a distance of 756 km.
Photo mosaic of Mercury, made at the approach of "Mariner-10" to this planet during the first flyby of Mercury near approaches to 7340km from March 29, 1974

Mercury moves around the sun in highly elliptical orbit, whose plane is inclined to the ecliptic plane at an angle of 7 ° 00'15 ". The distance of Mercury from the Sun varies from 46.08 to 68.86 million km million km. The period of revolution around the Sun ( Mercurian year) is 87.97 Earth days, while the average interval between identical phases (synodic period) 115.9 Earth days. Duration of solar day on Mercury is 176 Earth days. Mercury's distance from Earth varies from 82 to 217 million km. Maximum angular size of the planet as seen from Earth is 13 "minimum - 5." Period of Mercury on its axis is equal to 58,6461 ± 0,0005 days, which is 2 / 3 of the period of revolution around the sun. This is the result of tidal friction and torque of the gravitational forces from the Sun due to the fact that Mercury's mass distribution is not strictly concentric (center of mass is shifted toward the geometric center of the planet, the rotation uneven, "jerks"). Handling of Mercury around the Sun and its own rotation leads to that the duration of solar day on the planet is equal to three stellar Mercurian day or two Mercurian years and is about 175.92 Earth days.

Mercury's rotation axis is tilted to the plane of its orbit for no more than 3 °, so that significant seasonal changes on this planet should not exist. For observations from Earth Mercury - a difficult subject, as he visibly never removed from the Sun for more than 28 °, therefore it has to be seen always in the background of evening or dawn low in the sky. In addition, at this time of the phase of the planet (ie the angle between the directions at the planet from the Sun and the Earth) is close to 90 °, and the observer sees only the illuminated half of its disk.

13 times in a century Mercury passes across the solar disk. It happens in May or November, when the inferior conjunction of the planet is near the nodes of the orbit of Mercury. Mercury is projected on the solar disk and moves it to the direction from east to west. November's passage occurs twice as often as May. Over a period of 46 years, they usually observed four - three times at 13 and once in 7 years after the previous passage. Recently the November passage was observed in 1999, and the next will be held in 2006. Rarer May is better observed in the Northern Hemisphere, it is in Russia. For 46 years, as a rule, there are two passing in May - after 33 years and 13 years after the previous passage. Recently the May passage of Mercury was held May 9, 1970, and the next will be held May 7, 2003 and will be completely clear in Russia.

Size, shape and mass of Mercury

The shape of Mercury is close to the ball to the equatorial radius (2439 ± 1) km, which is roughly 2.6 times smaller than the Earth. The difference between the equatorial semiaxes of the ellipse of the planet is about 1 km equatorial and polar compression are negligible. Deviation of the geometric center of the planet (the ball) from the center of mass - about a mile. The surface area of Mercury in 6.8 times and the volume - at 17.8 times smaller than the Earth.

The mass of Mercury is approximately 18 times Earth's mass. The average density is close to the earth.
Temperature and topography of Mercury's surface
Close-up of Mercury's surface area with a lot of impact craters obtained Mariner 10 in 1974
Photo mosaic of the Caloris basin on Mercury, made on the basis of photographs obtained with the "Mariner" in 1974 Diameter Basin is 1300 km, and it is one of the biggest shock structures in the solar system. Mountain ring surrounding the cavity rises above its bottom to a height of 2 km.
As the closest planet to the Sun, Mercury gets from the central luminary is much more energy than, for example, the Earth (an average of 10 times). shz of elongated orbits the flow of energy from the sun varies by about a factor of two. Longer duration of day and night leads to the fact that the brightness temperature (as measured by infrared radiation in accordance with the law of thermal radiation Planck) to "daily" and "night" side of Mercury's surface at an average distance from the Sun can vary from about 700 K to 100 K (-180oC to 430 ° C). The temperature in the polar region reaches a night - 210oS and day under the scorching rays of the sun in the equatorial zone + 500oC. But already at a depth of several tens of centimeters wide fluctuations of temperature do not, that is a consequence of very low thermal conductivity of rocks.

Mercury's surface is covered with thousands of craters formed by collisions with meteorites and rocks that were formed when a young core cools and contracts, pulling the crust of the planet, as well as fragmented basaltic material type, quite dark. Judging by observations from Earth, and photos from the spacecraft, it is generally similar to the lunar surface, although the contrast between light and dark areas is less pronounced. Along with craters (generally less profound than on the Moon) is the hills and valleys.

  Up to 70% of the studied area is ancient, heavily cratered surface is pitted. The most important detail - Plain Heat (Caloris basin), the huge impact crater with a diameter of 1300 km (a quarter the diameter of the planet). Cavity was filled with lava and relatively flattened, the surface of the same type of capture and emission. Stroke occurred 3,800 million years ago, triggering a temporary revival of volcanic activity, which is basically stopped for 100 million years before. This led to a smoothing of areas in and around the basin. In the region of Mercury's surface, which is diametrically opposed to the point of impact, there is surprisingly chaotic structure created, apparently, the shock wave.
  Characteristic features found on Mercury - rugged cliffs (scarps), which takes the form of cliff height from several hundred to 3000 meters, it is believed they were formed by compression of the planetary crust in the cooling process. In some places they have to cross the walls of craters. Radar observations of Mercury at the end of 2001, showed the presence on its surface a large crater with a diameter 85 km. In structure it is similar to the crater Tycho on the Moon's surface, but may be considerably younger than the age of lunar formation 109 million years.

The atmosphere and physical fields

Above the surface of Mercury, there are traces of a very tenuous atmosphere containing, except helium and hydrogen, carbon dioxide, carbon, oxygen and noble gases (argon, neon). In 1985, in an atmosphere detected sodium atoms. The proximity of the sun makes a significant impact on Mercury is the solar wind. Due to this proximity is significant and tidal influence of the Sun on Mercury, which should lead to the emergence of the planet's surface electric field whose strength can be approximately twice that of "a field of clear weather" over the Earth's surface and differs from the comparative stability.

Mercury has a magnetic field. Magnetic dipole moment of Mercury is 4.9 × 1022 G • cm3, which is about four orders of magnitude smaller than the Earth, but because the field strength is inversely proportional to the cube of the radius of the planet, then Mercury and Earth are similar in magnitude.

Model the internal structure
Several models of the internal structure of Mercury. According to the most popular (albeit preliminary) view of the planet is hot, gradually the cooling iron-silicate core and shell, on the border between which the temperature can be close to 103 K. The share of core representing more than half the mass of the planet (about 70% weight and 75% overall diameter of the planet). Rocks contain about 6% iron, while mostly aluminum and calcium.

a) The ratio of the mass of the Sun to the mass of the planet (including the atmosphere).
c) compression as well (Re-Rp) / Re, where Re and Rp - equatorial and polar radii of the planets (respectively).

History of Discoveries
Date of Academic View
1530g N. Copernicus first time very accurately calculates the distance between the Sun and Mercury) in 376 AE.
1631g P. Gassendi on November 7 for the first time astronomers have observed the passage of Mercury across the solar disk prediction sh. Kepler. That repeats after 13 years, and sometimes after 7 years, but always either in May or in November. Mercury passes north or south of the solar equator. In our time, see May 7, 2003.
1859 U.ZH. Leverrier opened perihelion of the planet and by this time developed a theory of its motion.
1882 DV Schiaparelli Defines period of Mercury in 88 days.
1950 A. Dollfus using polarimetric studies showed that Mercury has a very rarefied atmosphere.
1965 p-m Arecibo radar With Gordon H. Pettengill and Ralph B. Deiss measured the orbital period of Mercury around the axis, receiving the result of 58.65 days.
1974 spacecraft Mariner 10 spacecraft in March for the first time began to study the planet. Produced by photographing the planet from a distance of up to 233,000 7340km when approaching on March 29 and Sept. 21 to a distance of 756km closer, and on March 16 1975 to a distance of 327km. Made about 4300 shots, on the basis of which a map of the western hemisphere of Mercury. Razreshaemost the third approach was 100m. Detected magnetic field is 100 times weaker than Earth, is confirmed by a discharged hydrogen-helium atmosphere, the measured temperature. Discovered a system of mountains and fissures that have nothing to do with the lunar and Martian.
1977 JN Lipsky publish catalog craters of Mercury