Of all the terrestrial planets in the Solar System, the geology of Mercury is the least understood. Reasons for this include Mercury's proximity to the Sun and the resultant dangers to spacecraft of intense solar radiation and high surface temperatures. Also, Mercury's period of rotation is a slow 58 Earth days, so that when NASA's Mariner 10 space probe flew past Mercury three times during 1974 and 1975, it was only able to observe the side facing the Sun during each pass. It is hoped that NASA's MESSENGER probe, launched in August 2004, will greatly contribute to our understanding when it enters orbit around Mercury in March 2011. A terrestrial planet or telluric planet is a planet which is primarily composed of silicate rocks. ... Presentation of the solar system (not to scale) The solar system comprises our Sun and the retinue of celestial objects gravitationally bound to it. ... Atmospheric characteristics Atmospheric pressure trace Potassium 31. ... The Sun (or Sol) is the star at the center of our Solar system. ... Solar irradiance spectrum at top of atmosphere. ... In astronomy, a rotation period is the time an astronomical object takes to complete one revolution around its rotation axis. ... Earth, also known as Terra, and (mostly in the 19th century) Tellus, is the third-closest planet to the Sun. ... NASA Logo Listen to this article · (info) This audio file was created from the revision dated 2005-09-01, and does not reflect subsequent edits to the article. ... The Mariner 10 probe. ... 1974 (MCMLXXIV) is a common year starting on Tuesday (click on link for calendar). ... 1975 (MCMLXXV) was a common year starting on Wednesday (the link is to a full 1975 calendar). ... the MESSENGER spacecraft The MErcury Surface, Space ENvironment, GEochemistry and Ranging (MESSENGER) is a NASA mission, launched August 3, 2004, designed to study the characteristics and environment of Mercury from orbit. ... Note: as an adjective (stressed on the second syllable instead of the first), august means honorable. ... 2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. ... March is the third month of the year in the Gregorian Calendar and one of seven Gregorian months with the length of 31 days. ... 2011 (MMXI) is a common year starting on Saturday of the Gregorian calendar. ...

Mariner 10 probe which imaged surface

The Mariner 10 was a probe sent to Mercury. ... The Mariner 10 was a probe sent to Mercury. ...

Mercury's geological history

Like the Moon and Mars, Mercury's geologic history is divided up into eras. From oldest to youngest, these are: the pre-Tolstojan, Tolstojan, Calorian, Mansurian, and Kuiperian. These ages are based on relative dating only.(1) Amongst the findings from the Opportunity rover is the presence of hematite on Mars in the form of small spheres on the Meridiani Planum. ... See also: ERA (disambiguation page). ... ...

After the formation of Mercury over four billion years ago, it received heavy bombardment of comets and asteroids that came to an end 3.8 billion years ago. During this period of intense crater formation, the surface received many impacts. Other massifs, such as the one that formed the Caloris Basin, were filled by magma from within the planet, which produced smooth intercrater plains similar to the maria found on the Moon. As the planet cooled and contracted, its surface began to crack; these surface cracks can be seen on top of other features, such as the craters and smoother plains – a clear indication that they are more recent. Mercury's period of vulcanism ended when the planet's mantle had contracted enough to prevent further lava from breaking through to the surface. This probably occurred at some point during its first 700 or 800 million years of history. In geology, a massif is a section of the Earths crust that is demarcated by faults or flexures. ... The Caloris Basin, also called Caloris Planitia, is an impact crater, on Mercury, which is ~1350km in diameter. ... A map showing the location of Mare Imbrium The Lunar maria (singular: mare, pronounced MAH-ray) are large, dark, basaltic plains on Earths Moon, formed by ancient basaltic flood eruptions caused by extremely large meteoroid impacts. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... This article is about volcanoes in geology. ... Look up Lava, ‘A‘a, or Pāhoehoe in Wiktionary, the free dictionary Lava is molten rock that a volcano expels during an eruption. ...

Since then, the only impacts have been the result of the planet being struck by stray asteroids and comets. An asteroid is a small, solid object in our Solar System, orbiting the Sun. ... Comet Hale-Bopp A comet is a small body in the solar system that orbits the sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both due primarily to the effects of solar radiation upon the comets nucleus, which itself is a minor planet...

References for (1):

• Map of Mercury (PDF, large image; bilingual)

• Paul Spudis, "The Geological History of Mercury" (PDF)

General characteristics of the surface

Map of Mercury

Caloris Basin

Image:Impactcraterformation lmb.png Creation of an impact crater

With a surface density of 5.44 g/cm³, the surface of Mercury is highly cratered, and those craters are uniformly distributed over the surface. The present surface exhibits such an abundant quantity of craters because Mercury's atmosphere is so thin that meteorites can easily reach the surface without disintegrating. The surface of Mercury has accumulated meteoric impacts since its creation over 4 billion years ago, and for this reason its surface, like those of the Moon and Mars registers the importance such impacts have in determining the duration of this period of craterization, which was very intense for about 3 billion years. Image File history File links Mercury_Caloris_Basin. ... This article is about impact craters, also known as meteor craters. ... Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... A meteorite is a small extraterrestrial body that reaches the Earths surface. ... Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... Amongst the findings from the Opportunity rover is the presence of hematite on Mars in the form of small spheres on the Meridiani Planum. ...

Apart from craters of diameters in the range of hundreds of meters to hundreds of kilometers, there are others of gigantic proportions such as Caloris, the largest structure on the surface of Mercury with a diameter of 1,300 km. The impact was so powerful that it caused lava eruptions from the crust of the planet and left a concentric ring surrounding the impact crater over 2 km tall. The consequences of Caloris are also impressive: it is widely accepted as the cause for the fractures and leaks on the opposite side of the planet. The Caloris Basin, also called Caloris Planitia, is an impact crater, on Mercury, which is ~1350km in diameter. ... Look up impact in Wiktionary, the free dictionary. ... Look up Lava, ‘A‘a, or Pāhoehoe in Wiktionary, the free dictionary Lava is molten rock that a volcano expels during an eruption. ... This article is about impact craters, also known as meteor craters. ...

Interior of Mercury.

These kinds of craters which have been filled with lava are known as seas in lunar geology. Image File history File links Mercury_inside_Lmb. ... Image File history File links Mercury_inside_Lmb. ... Exploring Shorty crater during the Apollo 17 mission to the Moon. ...

As on the Moon, craters in Mercury show the typical characteristics of an impact: the ejected debris forms banks around the crater shaped as linear extensions known as radii (or rays), the brightness of which is stronger because the terrain is relatively younger than the surrounding surface. Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ...

Other escarpments have also been seen crossing the planet's surface, in both the heavily cratered and flat areas. They are attributed to the cooling that Mercury has undergone since its formation, shrinking and causing the crust to realign itself.

The planet's high density (5.44 g/cm³) indicates that it has a core of 65% iron, accounting for somewhere about 75% of its diameter. This core is then surrounding by a 600 km thick mantle. As the cooling of the planet caused the core and mantle to shrink after its initial formation, Mercury' lost an estimated 2 to 4 km of its radius, which created the network of fissures visible on its surface.

Origin of the planet's high luminosity and the presence of ice

The first radar observations of Mercury were carried out by the radiotelescopes at Arecibo (Puerto Rico) and Goldstone (California, United States), with assistance from the U.S. National Radio Astronomy Observatory Very Large Array (VLA) facility in New Mexico. The transmissions sent from the NASA Deep Space Network site at Goldstone were at a power level of 460 kW at 8.51 GHz; the signals received by the VLA multi-dish array detected points of radar reflectivity (radar luminosity) with depolarized waves from Mercury's north pole. In contrast to an ordinary telescope, which produces visible light images, a radio telescope sees radio waves emitted by radio sources, typically by means of a large parabolic (dish) antenna, or arrays of them. ... The Arecibo Observatory is located in Arecibo, Puerto Rico on the north coast of the island. ... The Goldstone Deep Space Communications Complex (GDSCC) —commonly called the Goldstone Observatory— is located in Californias Mojave Desert (USA). ... State nickname: The Golden State Official languages English Capital Sacramento Largest city Los Angeles [[List of Governors of {{{Name}}}|Governor]] Arnold Schwarzenegger (R) [[List of United States Senators from {{{Name}}}|Senators]] Dianne Feinstein (D) Barbara Boxer (D) Area  - Total  - % water Ranked 3rd 410,000 km² 4. ... ... The National Radio Astronomy Observatory (NRAO) is an institution set up by the United States government for the purpose of radio astronomy. ... 27 independent radio dishes, 25m each For other uses of the acronym VLA see VLA (disambiguation) The Very Large Array (VLA) is a radio astronomy observatory located on the Plains of San Augustin, between the towns of Magdalena and Datil, some fifty miles (80 km) west of Socorro, New Mexico... State nickname: Land of Enchantment Official languages English and Spanish Capital Santa Fe Largest city Albuquerque Governor Bill Richardson (D) Senators Pete Domenici (R) Jeff Bingaman (D) Area  - Total  - % water Ranked 5th 315,194 km² 0. ... Deep Space Network (DSN) is an international network of radio antennas that supports interplanetary spacecraft missions, and radio and radar astronomy observations for the exploration of the solar system and the universe. ...

Radar maps of the surface of the planet were made using the Arecibo radiotelescope. The survey was conducted with 420 kW UHF band (2.4 GHz) radio waves which allowed for a 15 km resolution. This study not only confirmed the existence of the zones of high reflectivity and depolarization, but also found a number of new areas (bringing the total to 20) and was even able to survey the poles. It has been postulated that surface ice may be responsible for these phenomena. This article is about the radio frequency. ... A natural, 4 tonne, block of ice on a beach in Iceland Icicles Ice is the solid form of water. ...

The belief that Mercury has surface ice may seem absurd at first, given its proximity to the Sun and its subsequently high temperature (420°C by day and 180°C at night). Regardless, it could very well be ice that is responsible for the high luminosity levels, as the silicate rocks that compose most of the surface of Mercury have exactly the opposite effect on luminosity. The presence of ice may be explained by another discovery of the radar surveys from Earth: craters at Mercury's higher latitudes may be deep enough to shield the ice from direct sunlight. This article is about impact craters, also known as meteor craters. ...

At the South Pole, the location of a large zone of high reflectivity coincides with the location of the Chao Meng-Fu crater, and other small craters containing reflective areas have also been identified. Chao Meng-Fu is a crater (167km in diameter) on Mercury. ...

At the North Pole, the situation is more complicated; no one can correlate the radar images with the data from Mariner 10, due to minor differences in the images. It should also be emphasized that there are areas of high reflectivity that do not correspond to any known craters. The Mariner 10 probe. ...

The radar reflection of ice on Mercury is minor compared to that which would occur with pure ice. This may be due to powder deposition that does not cover the surface of the crater completely.

Origin of ice

Mercury is not unique in having craters that stand in permanent shadow; at the south pole of Earth's Moon there is a large crater (Aitken) where ice is possibly thought to exist. Ice on both Mercury and the Moon must have originated from external sources: comets in the case of the Moon, or meteorites in the case of Mercury. The existence of ice on certain meteorites has been proven; it is therefore conceivable for meteorite impacts to have deposited water in the permanent-shadow craters, where it would have remained for millions or billions of years. Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ... Aitken is a large lunar impact crater that lies on the far side of the Moon. ... Comet Hale-Bopp A comet is a small body in the solar system that orbits the sun and (at least occasionally) exhibits a coma (or atmosphere) and/or a tail — both due primarily to the effects of solar radiation upon the comets nucleus, which itself is a minor planet... A meteorite is a small extraterrestrial body that reaches the Earths surface. ...

Another hypothesis, which has not been confirmed, is that Mercury has an important flow of water from its interior. It has also not been proved that any mechanism, such as photodissociation, erosion due to solar wind, or small meteorite impact, causes the loss of ice in on the surface. Photodissociation is the breakup of molecules caused by exposure to photons. ... Severe soil erosion in a wheat field near Washington State University, USA. Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, movement in response to gravity, or living organisms (in the case of bioerosion). ... The plasma in the Solar Wind meeting the heliopause Ion storm redirects here. ...

The behavior of ice on other celestial bodies has its peculiarities. The high temperatures on the surface of Mercury, near 420°C, the emptiness of space (the atmosphere of Mercury is almost imperceptible), and solar rays contribute to the sublimation of ice into vapor and its escape into space. Sublimation of an element or substance is a conversion between the solid and the gaseous phases of matter, with no intermediate liquid stage. ...

Nevertheless, it is not thought that such behavior occurs with ice on Mercury because the location of ice at high latitudes makes it so that the temperature is very low. Inside the craters, where there is no solar light, temperatures fall to -171°C; on the polar plains, the temperature does not rise above -106°C.

The evidence for ice on Mercury has not been irrefutably corroborated, but is simply scientific speculation provoked by images of areas of high reflectivity and the coincidence of the existence of large craters in polar zones. It must be made clear, however, that this anomalous reflection could also be due to the existence of metallic sulfates or other materials with the same capacity for reflection. For alternative meanings see metal (disambiguation). ... Sulfate is the IUPAC name for the SO42- ion, consisting of a central sulfur atom single bonded to four tetrahedrally oriented oxygen atoms. ...

Mercury's atmosphere

The existence of an atmosphere on a planet is of great geological relevance, since the erosion caused by wind, changes in temperature levels, moisture levels, etc contribute to the modification of the landscape and the deterioration of materials. Atmosphere is the general name for a layer of gases that may surround a material body of sufficient mass. ... Severe soil erosion in a wheat field near Washington State University, USA. Erosion is the displacement of solids (soil, mud, rock, and so forth) by the agents of wind, water, ice, movement in response to gravity, or living organisms (in the case of bioerosion). ...

Mercury's atmosphere dissipated shortly after the planet's formation over four billion years ago because of the low level of gravity on the planet and, mainly, the effects of the solar wind. However, there are still traces of a very thin atmosphere with a pressure level of 10^-15 bar (which can be considered negligible). The existence of an atmosphere would also keep temperatures more or less stable despite the variations in sunlight levels between night and day; consequently, temperature variations in bodies without atmospheres (or with extremely weak atmospheres) are more pronounced. For example, during the day Mercury's surface reaches a temperature of 420°C, while at night it dips to –180°C. The plasma in the Solar Wind meeting the heliopause Ion storm redirects here. ... A bar (symbol bar) is a unit of pressure. ...

Due to the abrupt changes in the temperature, the type of interaction over the surface is related to the thermal agitation produced on the materials.

See also

• List of craters on Mercury
• List of geological features on Mercury

This is a list of named craters on Mercury. ... This is a list of geological features on Mercury. ...

References

• Stardate, Guide to the Solar System. Publicación de la University of Texas at Austin McDonald Observatory
• Our Solar System, A Geologic Snapshot. NASA (NP-157). May 1992.
• Fotografía: Mercury. NASA (LG-1997-12478-HQ)
  

This article draws heavily on the corresponding article in the Spanish-language Wikipedia, which was accessed in the version of June 26, 2005. June 26 is the 177th day of the year (178th in leap years) in the Gregorian Calendar, with 188 days remaining. ... 2005 (MMV) is a common year starting on Saturday of the Gregorian calendar. ...

Original references for Spanish article

• Ciencias de la Tierra. Una Introducción a la Geología Física (Earth Sciences, an Introduction to Physical Geology), by Edward J. Tarbuck y Frederick K. Lutgens. Prentice Hall (1999).
• "Hielo en Mercurio" ("Ice on Mercury"). El Universo, Enciclopedia de la Astronomía y el Espacio ("The Universe, Encyclopedia of Astronomy and the Space"), Editorial Planeta-De Agostini, p. 141-145. Volume 5. (1997)

External links

• Mariner 10
• Mercury on Nineplanets.org
• Information about Mercury
• MESSENGER probe