Mercury
MESSENGER false color image of Mercury
Epoch J2000
Aphelion69,816,900 km
0. The MErcury Surface Space ENvironment GEochemistry and Ranging ( MESSENGER) probe is a NASA Spacecraft, launched August 3, 2004 In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Astronomy, an epoch is a moment in time used as a reference for the Orbital elements of a Celestial body. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 466697 AU
Perihelion46,001,200 km
0. The astronomical unit ( AU or au or au or sometimes ua) is a unit of Length based on the distance from the Earth to the In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 307499 AU
Semi-major axis57,909,100 km
0. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae 387098 AU
Eccentricity0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 205630[2]
Orbital period87. The orbital period is the time taken for a given object to make one complete Orbit about another object 9691 d
(0. A day (symbol d is a unit of Time equivalent to 24 Hours and the duration of a single Rotation of planet Earth with respect to the 240846 a)
Synodic period115. In Astronomy, a Julian year (symbol a) is a unit of measurement of Time defined The orbital period is the time taken for a given object to make one complete Orbit about another object 88 d[2]
Average orbital speed47. The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it 87 km/s[2]
Mean anomaly174. In the study of orbital dynamics the mean anomaly of an orbiting body is the Angle the body would have traveled about the center of the orbit's Auxiliary circle 796°
Inclination7. Inclination in general is the Angle between a Reference plane and another plane or axis of direction 005°
3. 38° to Sun’s equator
Longitude of ascending node48. The longitude of the ascending node (☊ or Ω is one of the Orbital elements used to specify the Orbit of an object in space 331°
Argument of perihelion29. The argument of periapsis (or argument of perifocus) ( ω) is the Orbital element describing the Angle of an Orbiting body's periapsis 124°
SatellitesNone
Physical characteristics
Mean radius2,439. A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. 7 ± 1. 0 km[3][4]
0. 3829 Earths
Flattening< 0. Ellipticity redirects here For the mathematical topic of ellipticity see Elliptic operator. 0006[4]
Surface area7. Equation A spheroid centered at the origin and rotated about the z axis is defined by the implicit equation \left(\frac{x}{a}\right^2+\left(\frac{y}{a}\right^2+\left(\frac{z}{b}\right^2 48×107 km²
0. 108 Earths[3]
Volume6. The volume of any solid plasma vacuum or theoretical object is how much three- Dimensional space it occupies often quantified numerically 083×1010 km³
0. 054 Earths[3]
Mass3. Mass is a fundamental concept in Physics, roughly corresponding to the Intuitive idea of how much Matter there is in an object 3022×1023 kg
0. 055 Earths[3]
Mean density5. The density of a material is defined as its Mass per unit Volume: \rho = \frac{m}{V} Different materials usually have different 427 g/cm³[3]
Equatorial surface gravity3. The surface gravity, g, of an astronomical or other object is the Gravitational acceleration experienced at its surfacem/s²
0. 38 g[3]
Escape velocity4. g-force (also G-force, g-load) is a measurement of an object's Acceleration expressed in g s In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy 25 km/s[3]
Sidereal rotation
period
58. The rotation period of an astronomical object is the time it takes to complete one revolution around its Axis of rotation relative to the background stars 646 day (58 d 15. 5 h)[3]
Equatorial rotation velocity10. The hour (symbol h) is a unit of Time. It is not an SI unit but is accepted for use with the SI 892 km/h
Axial tilt2. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 11′ ± 0. 1′[5]
North pole right ascension18 h 44 min 2 s
281. Right ascension (abbrev RA; symbol α) is the Astronomical term for one of the two Coordinates of a point on the Celestial sphere 01°[2]
North pole declination61. In Astronomy, declination (abbrev dec or δ) is one of the two coordinates of the Equatorial coordinate system, the other being either 45°[2]
Albedo0. The albedo of an object is the extent to which it diffusely reflects light from the sun 119 (bond)
0. The Bond albedo is the fraction of power in the total electromagnetic radiation incident on an astronomical body that is scattered back out into space 106 (geom.)[2]
Surface temp.
0°N, 0°W
85°N, 0°W
minmeanmax
100 K340 K700 K
80 K200 K380 K
Apparent magnitudeup to −1. The geometric albedo of an astronomical body is the ratio of its actual brightness at zero phase angle (i Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 9[2]
Angular diameter4. The angular diameter of an object as seen from a given position is the "visual diameter" of the object measured as an angle 5" – 13"[2]
Atmosphere
Surface pressuretrace
Composition42% Molecular Oxygen
29. Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the 0% Sodium
22. Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 0% Hydrogen
6. Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 0% Helium
0. Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical 5% Potassium
Trace amounts of Argon, Nitrogen, Carbon dioxide, Water Vapor, Xenon, Krypton, & Neon[2]

Mercury (pronounced [ˈmɝkjʊəri] ) is the innermost and smallest planet in the solar system (since Pluto was re-labelled as a dwarf planet), orbiting the Sun once every 88 days. Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 This article pertains to the chemical element For other uses see Argon (disambiguation. Nitrogen (ˈnaɪtɹəʤɪn is a Chemical element that has the symbol N and Atomic number 7 and Atomic weight 14 Carbon dioxide ( Chemical formula:) is a Chemical compound composed of two Oxygen Atoms covalently bonded to a single Water is a common Chemical substance that is essential for the survival of all known forms of Life. Xenon (ˈzɛnɒn or) is a Chemical element represented by the symbol Xe. Krypton (ˈkrɪptən or /ˈkrɪptɒn/ from kryptos "hidden" is a Chemical element with the symbol Kr and Atomic number 36 Neon (ˈniːɒn is the Chemical element that has the symbol Ne and Atomic number 10 A planet, as defined by the International Astronomical Union (IAU is a celestial body Orbiting a Star or stellar remnant that is The Solar System consists of the Sun and those celestial objects bound to it by Gravity. A dwarf planet, as defined by the International Astronomical Union (IAU is a Celestial body Orbiting the Sun that is massive enough to be rounded In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The Sun (Sol is the Star at the center of the Solar System. Mercury is bright when viewed from Earth, ranging from −2. 0 to 5. 5 in apparent magnitude, but is not easily seen as its greatest angular separation from the Sun (greatest elongation) is only 28. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value (For other uses of elongation see Elongation) Elongation is an Astronomical term that refers to the angle between the Sun and a planet 3°: It can only be seen in morning and evening twilight. Twilight is the time before Sunrise, called Dawn, and the time after Sunset, called Dusk. Comparatively little is known about it; the first of two spacecraft to approach Mercury was Mariner 10 from 1974 to 1975, which mapped only about 45% of the planet’s surface. A spacecraft is a Vehicle or machine designed for Spaceflight. Mariner 10 was a robotic Space probe launched on November 3, 1973 to fly by the planets Mercury and Venus. [7] The second was the MESSENGER spacecraft, which mapped another 30% of the planet during its flyby of January 14, 2008. The MErcury Surface Space ENvironment GEochemistry and Ranging ( MESSENGER) probe is a NASA Spacecraft, launched August 3, 2004 Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common [7] MESSENGER will make two more passes by Mercury, followed by orbital insertion in 2011, and will survey and map the entire planet.

Physically, Mercury is similar in appearance to the Moon. It is heavily cratered, has no natural satellites and no substantial atmosphere. In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " It has a large iron core, which generates a magnetic field about 1% as strong as that of the Earth. Iron (ˈаɪɚn is a Chemical element with the symbol Fe (ferrum and Atomic number 26 The planetary core consists of the innermost layer(s of a Planet. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 [8] It is an exceptionally dense planet due to the large size of its core. The surface temperatures on Mercury range from about 90 to 700 K,[9] with the subsolar point being the hottest and the bottoms of craters near the poles being the coldest. The kelvin (symbol K) is a unit increment of Temperature and is one of the seven SI base units The Kelvin scale is a thermodynamic The subsolar point on a Planet is where its Sun is perceived to be directly overhead (in Zenith) A geographical pole, or geographic pole, is either of two fixed points on the surface of a spinning body or Planet, at 90 degrees from the Equator, based

Recorded observations of Mercury date back to at least the first millennium BC. Before the 4th century BC, Greek astronomers believed the planet to be two separate objects: one visible only at sunrise, which they called Apollo; the other visible only at sunset, which they called Hermes. Hermes ( Greek,, ˈhɝmiːz in Greek mythology, is the Olympian god of boundaries and of the travelers who cross them of Shepherds and [10] The English name for the planet comes from the Romans, who named it after the Roman god Mercury, which they equated with the Greek Hermes. Ancient Rome was a Civilization that grew out of a small agricultural community founded on the Italian Peninsula as early as the 10th century BC Roman mythology, or more appropriately Latin mythology, refers to the mythological beliefs of the Italic people inhabiting the region of Latium and its "Alipes" redirects here For the Centipede Genus, see Alipes (centipede. Hermes ( Greek,, ˈhɝmiːz in Greek mythology, is the Olympian god of boundaries and of the travelers who cross them of Shepherds and The astronomical symbol for Mercury is a stylized version of Hermes' caduceus. Astronomical symbols are symbols used to represent various Celestial objects theoretical constructs and observational events in Astronomy. The caduceus (/kəˈdjuːsiəs/ -ʃəs -ˈduː- κηρύκειον in Greek) or wand of Hermes is typically depicted as a short herald's staff [11]

## Internal structure

Mercury is one of four terrestrial planets, and is a rocky body like the Earth. A terrestrial planet, telluric planet or rocky planet is a Planet that is primarily composed of Silicate rocks Within our It is the smallest planet in the solar system, with an equatorial radius of 2439. The Solar System consists of the Sun and those celestial objects bound to it by Gravity. The equator (sometimes referred to colloquially as "the Line") is the intersection of the Earth 's surface with the plane perpendicular to the Remote Authentication Dial In User Service ( RADIUS) is a networking protocol that provides centralized access authorization and accounting management for people or computers 7 km. [2] Mercury is even smaller—albeit more massive—than the largest natural satellites in the solar system, Ganymede and Titan. This is a list of Solar System objects by radius, arranged in descending order of mean volumetric Radius. The tables below of Natural satellites in the Solar System are ordered from largest to smallest by average diameter A natural satellite or moon is a Celestial body that Orbits a Planet or smaller body which is called the primary. TemplateInfobox Planet.--> Ganymede (ˈgænɨmiːd, or as Greek TemplateInfobox Planet.--> Titan (ˈtaɪtən, or as Mercury consists of approximately 70% metallic and 30% silicate material. The M acro E xpansion T emplate A ttribute L anguage complements TAL, providing macros which allow the reuse of code across For the Artificial intelligence Androids of the 1990s Science fiction series Space Above and Beyond, see Silicate (AI [12] Mercury's density is the second highest in the Solar System at 5. 427 g/cm³, only slightly less than Earth’s density of 5. 515 g/cm³. [2] If the effect of gravitational compression were to be factored out, the materials of which Mercury is made would be denser, with an uncompressed density of 5. 3 g/cm³ versus Earth’s 4. 4 g/cm³. [13]

1. Crust—100–300 km thick
2. Mantle—600 km thick

Mercury’s density can be used to infer details of its inner structure. While the Earth’s high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller and its inner regions are not nearly as strongly compressed. The planetary core consists of the innermost layer(s of a Planet. Therefore, for it to have such a high density, its core must be large and rich in iron. [14] Geologists estimate that Mercury’s core occupies about 42% of its volume; for Earth this proportion is 17%. Recent research strongly suggests Mercury has a molten core. [15][16]

Surrounding the core is a 600 km mantle. The mantle is a part of an Astronomical object. The interior of the Earth, similar to the other Terrestrial planets, is Chemically divided It is generally thought that early in Mercury’s history, a giant impact with a body several hundred kilometers across stripped the planet of much of its original mantle material, resulting in the relatively thin mantle compared to the sizable core. [17]

Based on data from the Mariner 10 mission and Earth-based observation, Mercury’s crust is believed to be 100–300 km thick. In Geology, a crust is the outermost solid shell of a planet or moon [18] One distinctive feature of Mercury’s surface are numerous narrow ridges, some extending over several hundred kilometers. It is believed that these were formed as Mercury’s core and mantle cooled and contracted at a time when the crust had already solidified. [19]

Mercury's core has a higher iron content than that of any other major planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory is that Mercury originally had a metal-silicate ratio similar to common chondrite meteors, thought to be typical of the Solar System's rocky matter, and a mass approximately 2. Chondrites are stony Meteorites that have not been modified due to Melting or Differentiation of the parent body 25 times its current mass. [17] However, early in the solar system’s history, Mercury may have been struck by a planetesimal of approximately 1/6 that mass. Planetesimals are solid objects thought to exist in Protoplanetary disks and in Debris disks A widely accepted theory of planet formation the so-called planetesimal [17] The impact would have stripped away much of the original crust and mantle, leaving the core behind as a relatively major component. [17] A similar process has been proposed to explain the formation of Earth’s Moon (see giant impact theory). [17]

Alternatively, Mercury may have formed from the solar nebula before the Sun’s energy output had stabilized. The formation and evolution of the Solar System is estimated to have begun In Physics and other Sciences energy (from the Greek grc ἐνέργεια - Energeia, "activity operation" from grc ἐνεργός The planet would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K, and possibly even as high as 10,000 K. A protostar is a large object that forms by contraction out of the gas of a Giant molecular cloud in the Interstellar medium. [20] Much of Mercury’s surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" which could have been carried away by the solar wind. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. [20]

A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting, which meant that lighter particles were lost from the accreting material. The formation and evolution of the Solar System is estimated to have begun In Fluid dynamics, drag (sometimes called fluid resistance) is the force that resists the movement of a Solid object through a Fluid (a [21] Each of these hypotheses predicts a different surface composition, and two upcoming space missions MESSENGER and BepiColombo both aim to make observations to test them. The MErcury Surface Space ENvironment GEochemistry and Ranging ( MESSENGER) probe is a NASA Spacecraft, launched August 3, 2004 BepiColombo is a joint Cornerstone mission of the European Space Agency (ESA and the Japan Aerospace Exploration Agency (JAXA to the planet Mercury [22][23]

## Surface geology

First high-resolution image of Mercury transmitted by MESSENGER (false color)
Main article: Geology of Mercury

Mercury’s surface is overall very similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. The surface of Mercury is dominated by Impact craters, and lava plains similar in some respects to the Lunar maria. The lunar maria (singular mare, two syllables are large dark Basaltic plains on Earth 's Moon, formed by ancient Volcanic eruptions Since our knowledge of Mercury's geology has been based on the 1975 Mariner flyby and terrestrial observations, it is the least understood of the terrestrial planets. The surface of Mercury is dominated by Impact craters, and lava plains similar in some respects to the Lunar maria. [16] As data from the recent MESSENGER flyby is processed this knowledge will increase. For example, an unusual crater with radiating troughs has been discovered which scientists are calling "the spider. "[24]

Albedo features refer to areas of markedly different reflectivity, as seen by telescopic observation. The albedo of an object is the extent to which it diffusely reflects light from the sun Mercury also possesses Dorsa (also called "wrinkle-ridges"), Moon-like highlands, Montes (mountains), Planitiae, or plains, Rupes (escarpments), and Valles (valleys). A wrinkle-ridge is a type of feature commonly found on Lunar maria. The term highland is used to denote any Mountainous region or elevated mountainous Plateau. In Geography, a plain is an area of land with relatively low relief — meaning that it is flat Rupes is the Latin word for 'cliff' It is used in Planetary geology to refer to Escarpments on other Planets such as Mercury, and In Geomorphology, an escarpment is a transition zone between different physiogeographic provinces that involves a sharp steep Elevation differential characterized Vallis (plural valles) is the Latin word for Valley. It is used in Planetary geology for the naming of Landform In Geology, a valley (also called a vale, dale, glen or strath and near or in Appalachia, a draw) is [25][26]

Mercury was heavily bombarded by comets and asteroids during and shortly following its formation 4. A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — Asteroids, sometimes called Minor planets or planetoids', are bodies—primarily of the inner Solar System —that are smaller than planets but 6 billion years ago, as well as during a possibly separate subsequent episode called the late heavy bombardment that came to an end 3. The Late Heavy Bombardment (commonly referred to as the lunar cataclysm, or LHB) is a period of time approximately 3800 to 4100 million years ago ( mya 8 billion years ago. [27] During this period of intense crater formation, the planet received impacts over its entire surface,[26] facilitated by the lack of any atmosphere to slow impactors down. An atmosphere (from Greek ατμός - atmos, " Vapor " + σφαίρα - sphaira, " Sphere " [28] During this time the planet was volcanically active; basins such as the Caloris Basin were filled by magma from within the planet, which produced smooth plains similar to the maria found on the Moon. Plate tectonics and hotspots Divergent plate boundaries At the The Caloris Basin, also called Caloris Planitia, is an Impact crater on Mercury about 1550 km in Diameter, one of the largest Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet The lunar maria (singular mare, two syllables are large dark Basaltic plains on Earth 's Moon, formed by ancient Volcanic eruptions [29][30]

### Impact basins and craters

Mercury’s Caloris Basin is one of the largest impact features in the Solar System. The Caloris Basin, also called Caloris Planitia, is an Impact crater on Mercury about 1550 km in Diameter, one of the largest

Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins hundreds of kilometers across. In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body They appear in all states of degradation, from relatively fresh rayed craters to highly degraded crater remnants. Mercurian craters differ subtly from lunar craters in that the area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity. [31]

The largest known craters are Caloris Basin, with a diameter of 1550 km,[32] and the Skinakas Basin with an outer-ring diameter of 2,300 km. The Skinakas Basin is the informal name given to a structure on Mercury that appears to be an extremely large Impact basin. [33] The impact that created the Caloris Basin was so powerful that it caused lava eruptions and left a concentric ring over 2 km tall surrounding the impact crater. Lava is molten rock expelled by a Volcano during an eruption When first expelled from a volcanic vent it is a Liquid at Temperatures In the broadest sense the term impact crater can be applied to any depression natural or manmade resulting from the high velocity impact of a projectile with larger body At the antipode of the Caloris Basin is a large region of unusual, hilly terrain known as the "Weird Terrain". The antipodes refer to lands and peoples located on the opposite side of the World compared to the speaker One hypothesis for its origin is that shock waves generated during the Caloris impact traveled around the planet, converging at the basin’s antipode (180 degrees away). The resulting high stresses fractured the surface. [34] Alternatively, it has been suggested that this terrain formed as a result of the convergence of ejecta at this basin’s antipode. [35]

Overall about 15 impact basins have been identified on the imaged part of Mercury. Other notable basins include the 400 km wide, multi-ring, Tolstoj Basin which has an ejecta blanket extending up to 500 km from its rim, and its floor has been filled by smooth plains materials. Tolstoj is a large ancient Impact crater at latitude -15 longitude 165 on Mercury. Beethoven Basin also has a similar-sized ejecta blanket and a 625 km diameter rim. Beethoven is a crater at latitude -20 longitude 124 on Mercury. [31] Like the Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including Solar wind and micrometeorite impacts. Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. A Micrometeoroid (also micrometeorite, micrometeor) is a tiny Meteoroid; a small particle of rock in space usually weighing less than a Gram [36]

### Plains

There are two geologically distinct plains regions on Mercury. [37][31] Gently rolling, hilly plains in the regions between craters are Mercury's oldest visible surfaces,[31] predating the heavily cratered terrain. The inter-crater plains appear to have obliterated many earlier craters, and show a general paucity of smaller craters below about 30 km in diameter. [37] It is not clear whether they are of volcanic or impact origin. [37] The inter-crater plains are distributed roughly uniformly over the entire surface of the planet.

The so-called “Weird Terrain” was formed by the Caloris Basin impact at its antipodal point. The Caloris Basin, also called Caloris Planitia, is an Impact crater on Mercury about 1550 km in Diameter, one of the largest

Smooth plains are widespread flat areas which fill depressions of various sizes and bear a strong resemblance to the lunar maria. Notably, they fill a wide ring surrounding the Caloris Basin. An appreciable difference between these plains and lunar maria is that the smooth plains of Mercury have the same albedo as the older inter-crater plains. Despite a lack of unequivocally volcanic characteristics, the localisation and rounded, lobate shape of these plains strongly support volcanic origins. [31] All the Mercurian smooth plains formed significantly later than the Caloris basin, as evidenced by appreciably smaller crater densities than on the Caloris ejecta blanket. [31] The floor of the Caloris Basin is also filled by a geologically distinct flat plain, broken up by ridges and fractures in a roughly polygonal pattern. The Caloris Basin, also called Caloris Planitia, is an Impact crater on Mercury about 1550 km in Diameter, one of the largest It is not clear whether they are volcanic lavas induced by the impact, or a large sheet of impact melt. [31]

One unusual feature of the planet’s surface is the numerous compression folds, or rupes, which crisscross the plains. Rupes is the Latin word for 'cliff' It is used in Planetary geology to refer to Escarpments on other Planets such as Mercury, and It is thought that as the planet’s interior cooled, it contracted and its surface began to deform. The folds can be seen on top of other features, such as craters and smoother plains, indicating that they are more recent. [38] Mercury’s surface is also flexed by significant tidal bulges raised by the Sun—the Sun’s tides on Mercury are about 17 times stronger than the Moon’s on Earth. The tidal force is a secondary effect of the Force of Gravity and is responsible for the Tides It arises because the gravitational acceleration experienced The Sun (Sol is the Star at the center of the Solar System. [39]

## Surface conditions and atmosphere

The mean surface temperature of Mercury is 442. In Statistics, mean has two related meanings the Arithmetic mean (and is distinguished from the Geometric mean or Harmonic mean Temperature is a physical property of a system that underlies the common notions of hot and cold something that is hotter generally has the greater temperature 5 K,[2] but it ranges from 100 K to 700 K,[40] due to the absence of an atmosphere. On the dark side of the planet, temperatures average 110 K. [41] The intensity of sunlight on Mercury’s surface ranges between 4. Sunlight, in the broad sense is the total spectrum of the Electromagnetic radiation given off by the Sun. 59 and 10. 61 times the solar constant (1370Wm−2). [42]

Radar image of Mercury's north pole

Despite the generally extremely high temperature of its surface, observations strongly suggest that ice exists on Mercury. Ice is a Solid phase, usually crystalline, of a Non-metalic substance that is liquid or gas at Room temperature, such as Ammonia The floors of some deep craters near the poles are never exposed to direct sunlight, and temperatures there remain far lower than the global average. Water ice strongly reflects radar, and observations by the 70m Goldstone telescope and the VLA in the early 1990s revealed that there are patches of very high radar reflection near the poles. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships The Goldstone Deep Space Communications Complex ( GDSCC) &mdashcommonly called the Goldstone Observatory &mdash is located in California 's Mojave Desert The Very Large Array ( VLA) is a Radio astronomy Observatory located on the Plains of San Augustin, between the towns of Magdalena [43] While ice is not the only possible cause of these reflective regions, astronomers believe it is the most likely. [44]

The icy regions are believed to be covered to a depth of only a few meters, and contain about 1014–1015 kg of ice. [45] By comparison, the Antarctic ice sheet on Earth has a mass of about 4×1018 kg, and Mars’ south polar cap contains about 1016 kg of water. [45] The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet’s interior or deposition by impacts of comets. Outgassing (sometimes called offgassing, particularly when in reference to indoor Air quality is the slow release of a Gas that was trapped A comet is a small Solar System body that orbits the Sun and when close enough to the Sun exhibits a visible coma (atmosphere or a tail — [45]

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

Mercury is too small for its gravity to retain any significant atmosphere over long periods of time; however, it does have a tenuous atmosphere containing hydrogen, helium, oxygen, sodium, calcium and potassium. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University EARTH was a short-lived Japanese vocal trio which released 6 singles and 1 album between 2000 and 2001 Gravitation is a natural Phenomenon by which objects with Mass attract one another Hydrogen (ˈhaɪdrədʒən is the Chemical element with Atomic number 1 Helium ( He) is a colorless odorless tasteless non-toxic Inert Monatomic Chemical Oxygen (from the Greek roots ὀξύς (oxys (acid literally "sharp" from the taste of acids and -γενής (-genēs (producer literally begetteris the Sodium (ˈsoʊdiəm is an element which has the symbol Na( Latin natrium, from Arabic natrun) atomic number 11 atomic mass 22 Calcium (ˈkælsiəm is the Chemical element with the symbol Ca and Atomic number 20 Potassium (pəˈtæsiəm is a Chemical element. It has the symbol K (kalium from qalīy Atomic number 19 and Atomic mass 39 This atmosphere is not stable—atoms are continuously lost and replenished from a variety of sources. Hydrogen and helium atoms probably come from the solar wind, diffusing into Mercury’s magnetosphere before later escaping back into space. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. Diffusion is the net movement of particles (typically molecules from an area of high concentration to an area of low concentration by uncoordinated random movement Radioactive decay of elements within Mercury’s crust is another source of helium, as well as sodium and potassium. Radioactive decay is the process in which an unstable Atomic nucleus loses energy by emitting ionizing particles and Radiation. Water vapor is probably present, being brought to Mercury by comets striking its surface. [46]

Sodium and potassium were discovered in the atmosphere during the 1980s, and are believed to result primarily from the vaporization of surface rock struck by micrometeorite impacts. Due to the ability of these materials to diffuse sunlight, Earth-based observers can readily detect their composition in the atmosphere. Studies indicate that, at times, Sodium emissions are localized at points that correspond to the planet's magnetic dipoles. This would indicate some interaction between the magnetosphere and the planet's surface. [47]

## Magnetic field and magnetosphere

Graph showing relative strength of Mercury's magnetic field

Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global, magnetic field. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges According to measurements taken by Mariner 10, it is about 1. 1% as strong as the Earth’s. The magnetic field strength at the Mercurian equator is about 300 nT. The tesla (symbol T) is the SI derived unit of Magnetic field B (which is also known as "magnetic flux density" and "magnetic [48][49] Like that of Earth, Mercury's magnetic field is dipolar in nature. In physics there are two kinds of dipoles ( Hellènic: di(s- = two- and pòla = pivot hinge An electric dipole is a [47] Unlike Earth, however, Mercury's poles are nearly aligned with the planet's spin axis. [50] Measurements from both the Mariner 10 and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable. [50]

It is likely that this magnetic field is generated by way of a Dynamo effect, in a manner similar to the magnetic field of Earth. The dynamo theory proposes a mechanism by which a celestial body such as the Earth generates a Magnetic field. [51][52] This dynamo effect would result from the circulation of the planet's iron-rich liquid core. Particularly strong tidal effects caused by the planet's high orbital eccentricity would serve to keep the core in the liquid state necessary for this dynamo effect. [53]

Mercury’s magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. The planet's magnetosphere, though small enough to fit within the Earth,[47] is strong enough to trap solar wind plasma. This contributes to the space weathering of the planet's surface. Space weathering is a blanket term used for a number of processes that act on any body exposed to the harsh space environment [50] Observations taken by the Mariner 10 spacecraft detected this low energy plasma in the magnetosphere of the planet's nightside. Bursts of energetic particles were detected in the planet's magnetotail, which indicates a dynamic quality to the planet's magnetosphere. [47]

## Orbit and rotation

Orbit of Mercury (yellow)

Mercury has the most eccentric orbit of all the planets; its eccentricity is 0. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape 21 with its distance from the Sun ranging from 46,000,000 to 70,000,000 kilometers. It takes 88 days to complete an orbit. The diagram on the left illustrates the effects of the eccentricity, showing Mercury’s orbit overlaid with a circular orbit having the same semi-major axis. In Geometry, the semi-major axis (also semimajor axis) is used to describe the dimensions of ellipses and hyperbolae The higher velocity of the planet when it is near perihelion is clear from the greater distance it covers in each 5-day interval. The size of the spheres, inversely proportional to their distance from the Sun, is used to illustrate the varying heliocentric distance. This varying distance to the Sun, combined with a 3:2 spin-orbit resonance of the planet’s rotation around its axis, result in complex variations of the surface temperature. [12]

Mercury’s orbit is inclined by 7° to the plane of Earth’s orbit (the ecliptic), as shown in the diagram on the left. The ecliptic is the apparent path that the Sun traces out in the sky during the year As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between the Earth and the Sun. Transit of Mercury Closeup - Nov 8 2006jpg|right|thumb|300px|Close-up of Mercury during the Nov This occurs about every seven years on average. [54]

Orbit of Mercury as seen from the ascending node (bottom) and from 10° above (top)

Functionally, Mercury’s axial tilt is nonexistent,[55][56] with measurements as low as 0. In Astronomy, axial tilt is the Inclination angle of a planet's rotational axis in relation to its orbital plane. 027°. [5] This is significantly smaller than that of Jupiter, which boasts the second smallest axial tilt of all planets at 3. 1 degrees. This means an observer at Mercury’s equator during local noon would never see the Sun more than 1/30[a] of one degree north or south of the zenith. In broad terms the zenith is the direction pointing directly above a particular location ( Perpendicular, Orthogonal) Conversely, at the poles the Sun never rises more than 2. 1′ above the horizon. [5]

At certain points on Mercury’s surface, an observer would be able to see the Sun rise about halfway, then reverse and set before rising again, all within the same Mercurian day. This is because approximately four days prior to perihelion, Mercury’s angular orbital velocity exactly equals its angular rotational velocity so that the Sun’s apparent motion ceases; at perihelion, Mercury’s angular orbital velocity then exceeds the angular rotational velocity. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it Rotational speed (sometimes called speed of revolution) indicates for example how fast a motor is running Apparent motion occurs when a stimulus is flashed in one location followed by another identical stimulus flashed in another location Thus, the Sun appears to move in a retrograde direction. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. Four days after perihelion, the Sun’s normal apparent motion resumes at these points. [12]

During the 19th century, French mathematician Le Verrier noticed that that the slow precession of Mercury’s orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets. At its introduction in 1915 the general theory of relativity did not have a solid empirical foundation At its introduction in 1915 the general theory of relativity did not have a solid empirical foundation A mathematician is a person whose primary area of study and research is the field of Mathematics. Urbain Jean Joseph Le Verrier ( March 11, 1811 &ndash September 23, 1877) was a French Mathematician who specialized in Celestial Precession refers to a change in the direction of the axis of a rotating object Classical mechanics is used for describing the motion of Macroscopic objects from Projectiles to parts of Machinery, as well as Astronomical objects He proposed that another planet might exist in an orbit even closer to the Sun to account for this perturbation. (Other explanations considered included a slight oblateness of the Sun. ) The success of the search for Neptune based on its perturbations of the orbit of Uranus led astronomers to place great faith in this explanation, and the hypothetical planet was even named Vulcan. Neptune ( English|AmE] ] is the eighth and farthest Planet from the Sun in the Solar System. Vulcan was a small Planet proposed to exist in an Orbit between Mercury and the Sun in a 19th-century hypothesis However, no such planet was ever found. [57]

In the early 20th century, Albert Einstein’s General Theory of Relativity provided the explanation for the observed precession. Albert Einstein ( German: ˈalbɐt ˈaɪ̯nʃtaɪ̯n; English: ˈælbɝt ˈaɪnstaɪn (14 March 1879 – 18 April 1955 was a German -born theoretical General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 The effect is very small: the Mercurian relativistic perihelion advance excess is just 42. 98 arcseconds per century, therefore it requires a little over twelve million orbits for a full excess turn. A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60 of one degree. Similar, but much smaller effects, operate for other planets, being 8. 62 arcseconds per century for Venus, 3. 84 for Earth, 1. 35 for Mars, and 10. 05 for 1566 Icarus. [58][59]

After one orbit, Mercury has rotated 1. 5 times, so after two complete orbits the same hemisphere is again illuminated.

### Spin–orbit resonance

For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and keeping the same face directed towards the Sun at all times, in the same way that the same side of the Moon always faces the Earth. A separate article treats the phenomenon of Tidal resonance in Oceanography. A rotation is a movement of an object in a circular motion A two- Dimensional object rotates around a center (or point) of rotation However, radar observations in 1965 proved that the planet has a 3:2 spin–orbit resonance, rotating three times for every two revolutions around the Sun; the eccentricity of Mercury’s orbit makes this resonance stable—at perihelion, when the solar tide is strongest, the Sun is nearly still in Mercury’s sky. Radar is a system that uses electromagnetic waves to identify the range altitude direction or speed of both moving and fixed objects such as Aircraft, ships [60]

The original reason astronomers thought it was synchronously locked was that whenever Mercury was best placed for observation, it was always at the same point in its 3:2 resonance, hence showing the same face. Due to Mercury’s 3:2 spin–orbit resonance, a solar day (the length between two meridian transits of the Sun) lasts about 176 Earth days. Solar times are measures of the apparent position of the Sun on the Celestial sphere. This article is about the astronomical concept For other uses of the word see Meridian. The term transit or astronomical transit has three meanings in astronomy A transit is the astronomical event that occurs when one [12] A sidereal day (the period of rotation) lasts about 58. Sidereal time is a measure of the position of the Earth in its rotation around its axis or time measured by the apparent Diurnal motion of the Vernal equinox 7 Earth days. [12]

Orbital simulations indicate that the eccentricity of Mercury’s orbit varies chaotically from 0 (circular) to a very high 0. In Mathematics, chaos theory describes the behavior of certain dynamical systems – that is systems whose state evolves with time – that may exhibit dynamics that 47 over millions of years. [12] This is thought to explain Mercury’s 3:2 spin-orbit resonance (rather than the more usual 1:1), since this state is more likely to arise during a period of high eccentricity. [61]

## Observation

Mercury’s apparent magnitude varies between about −2. The apparent magnitude ( m) of a celestial body is a measure of its Brightness as seen by an observer on Earth, normalized to the value 0—brighter than Sirius—and 5. Sirius is the brightest star in the night sky with a visual Apparent magnitude of &minus1 5. [62] Observation of Mercury is complicated by its proximity to the Sun, as it is lost in the Sun’s glare for much of the time. Mercury can be observed for only a brief period during either morning or evening twilight. The Hubble Space Telescope cannot observe Mercury at all, due to safety procedures which prevent its pointing too close to the Sun. The Hubble Space Telescope ( HST; also known colloquially as "the Hubble" or just "Hubble" is a space telescope that was carried into [63]

Like the Moon, Mercury exhibits phases as seen from Earth, being "new" at inferior conjunction and “full” at superior conjunction. Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth Conjunction is a term used in Positional astronomy and Astrology. Conjunction is a term used in Positional astronomy and Astrology. The planet is rendered invisible on both of these occasions by virtue of its rising and setting in concert with the Sun in each case. The first and last quarter phases occur at greatest elongation east and west, respectively, when Mercury's separation from the Sun ranges anywhere from 17. (For other uses of elongation see Elongation) Elongation is an Astronomical term that refers to the angle between the Sun and a planet 9° at perihelion to 27. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from 8° at aphelion. In Celestial mechanics, an apsis, plural apsides (ˈæpsɨdɪːz is the point of greatest or least distance of the Elliptical orbit of an object from [64][65] At greatest elongation west, Mercury rises earliest before the Sun, and at greatest elongation east, it sets latest after the Sun. [66]

Mercury attains inferior conjunction every 116 days on average,[2] but this interval can range from 111 days to 121 days due to the planet’s eccentric orbit. Mercury can come as close as 77. 3 million km to the Earth,[2] but currently it does not come closer than 82 million km from the Earth. [65] Its period of retrograde motion as seen from Earth can vary from 8 to 15 days on either side of inferior conjunction. Direct motion is the motion of a Planetary body in a direction similar to that of other bodies within its system and is sometimes called prograde motion. This large range also arises from the planet’s high orbital eccentricity. In Astrodynamics, under standard assumptions, any Orbit must be of Conic section shape [12]

Mercury is more often easily visible from Earth’s Southern Hemisphere than from its Northern Hemisphere; this is because its maximum possible elongations west of the Sun always occur when it is early autumn in the Southern Hemisphere, while its maximum possible eastern elongations happen when the Southern Hemisphere is having its late winter season. Southern Hemisphere is the half of a Planet that is South of the Equator —the word hemisphere literally means 'half ball' Northern Hemisphere is the half of a Planet that is North of the Equator —the word hemisphere literally means 'half ball' [66] In both of these cases, the angle Mercury strikes with the ecliptic is maximized, allowing it to rise several hours before the Sun in the former instance and not set until several hours after sundown in the latter in countries located at southern temperate zone latitudes, such as Argentina and New Zealand. The ecliptic is the apparent path that the Sun traces out in the sky during the year For a topic outline on this subject see List of basic Argentina topics. New Zealand is an Island country in the south-western Pacific Ocean comprising two main landmasses (the North Island and the South Island [66] By contrast, at northern temperate latitudes, Mercury is never above the horizon of a more-or-less fully dark night sky. Mercury can also, like several other planets and the brightest stars, be seen during a total solar eclipse. A solar eclipse occurs when the Moon passes between the Sun and the Earth so that the Sun is wholly or partially obscured [67]

Mercury is brightest as seen from Earth when it is at a gibbous phase, between either quarter phase and full. Lunar phase (or Moon phase refers to the appearance of the illuminated portion of the Moon as seen by an observer usually on Earth Although the planet is further away from Earth when it is gibbous than when it is a crescent, the greater illuminated area visible more than compensates for the greater distance. [62] The opposite is true for Venus, which appears brightest when it is a thin crescent, because it is much closer to Earth than when gibbous. [68]

## Studies of Mercury

### Ancient astronomers

The earliest known recorded observations of Mercury are from the MUL.APIN tablets. MULAPIN is a general compendium that deals with many diverse aspects of Babylonian astrology. These observations were most likely made by an Assyrian astronomer around the 14th century BC. Early history The most Neolithic site in Assyria is at Tell Hassuna, the center of the Hassuna culture [69] The cuniform name used to designate Mercury on the MUL. APIN tablets is transcribed as UDU. IDIM. GU4. UD ("the jumping planet"). [b][70] Babylonian records of Mercury date back to the 1st millennium BC. The Babylonians called the planet Nabu after the messenger to the Gods in their mythology. Nabu is the Babylonian god of Wisdom and Writing, worshipped by Babylonians as the son of Marduk and his consort Sarpanitum, The word mythology (from the Greek grc μυθολογία mythología, meaning "a story-telling a legendary lore" [71]

The ancient Greeks of Hesiod's time knew the planet as Στίλβων (Stilbon), meaning "the gleaming", and Ἑρμάων (Hermaon). The term ancient Greece refers to the period of Greek history lasting from the Greek Dark Ages ca Hesiod ( Greek: Hesiodos) was an early Greek Poet and Rhapsode, who presumably lived around 700 BCE [72] Later Greeks called the planet Apollo when it was visible in the morning sky and Hermes when visible in the evening. Hermes ( Greek,, ˈhɝmiːz in Greek mythology, is the Olympian god of boundaries and of the travelers who cross them of Shepherds and Around the 4th century BC, however, Greek astronomers came to understand that the two names referred to the same body. The Romans named the planet after the Roman messenger god, Mercury (Latin Mercurius), which they equated with the Greek Hermes. "Alipes" redirects here For the Centipede Genus, see Alipes (centipede. Hermes ( Greek,, ˈhɝmiːz in Greek mythology, is the Olympian god of boundaries and of the travelers who cross them of Shepherds and [10][73]

In ancient China, Mercury was known as Ch'en-Hsing, the Hour Star. Chinese civilization originated in various city-states along the Yellow River ( valley in the Neolithic era It was associated with the direction north and the phase of water in the Wu Xing. In traditional Chinese philosophy, natural phenomena can be classified into the Wu Xing ( or the Five Phases, usually translated as five elements, [74] Hindu mythology used the name Budha for Mercury, and this god was thought to preside over Wednesday. Hindu mythology is the large body of Mythology related to Hinduism, notably as contained in Sanskrit literature, such as the Sanskrit epics and In Hindu mythology, Budha (Sanskrit बुध not to be confused with Buddha) is the name for the planet Mercury, a son of Chandra (the [75] The god Odin (or Woden) of Germanic paganism was also associated with the planet Mercury and the name Wednesday was derived from Woden's day. Odin (ˈoʊdɪn from Old Norse Óðinn) is considered the chief god in Norse paganism. Germanic paganism refers to the religious beliefs of the Germanic peoples preceding Christianization. [76] The Maya may have represented Mercury as an owl (or possibly four owls; two for the morning aspect and two for the evening) that served as a messenger to the underworld. In the study of Mythology and Religion, the underworld (gr κάτω κόσμος) is a generic term approximately equivalent to the lay term Afterlife [77]

### Ground-based telescopic research

Transit of Mercury. Transit of Mercury Closeup - Nov 8 2006jpg|right|thumb|300px|Close-up of Mercury during the Nov Mercury is the small dot in the lower center, in front of the sun. The dark area on the left of the solar disk is a sunspot.

The first telescopic observations of Mercury were made by Galileo in the early 17th century. A telescope is an instrument designed for the observation of remote objects and the collection of Electromagnetic radiation. Galileo Galilei (15 February 1564 &ndash 8 January 1642 was a Tuscan ( Italian) Physicist, Mathematician, Astronomer, and Philosopher Although he observed phases when he looked at Venus, his telescope was not powerful enough to see the phases of Mercury. Planetary phase is the term used to describe the appearance of the illuminated section of a Planet. In 1631 Pierre Gassendi made the first observations of the transit of a planet across the Sun when he saw a transit of Mercury predicted by Johannes Kepler. Pierre Gassendi ( January 22, 1592 &ndash October 24, 1655) was a French Philosopher, priest, Scientist Johannes Kepler (ˈkɛplɚ ( December 27 1571 &ndash November 15 1630) was a German Mathematician, Astronomer In 1639 Giovanni Zupi used a telescope to discover that the planet had orbital phases similar to Venus and the Moon. Giovanni Battista Zupi or Zupus (c 1590 &ndash 1650 was an Italian Astronomer, Mathematician, and Jesuit Priest. In Physics, an orbit is the gravitationally curved path of one object around a point or another body for example the gravitational orbit of a planet around a star The observation demonstrated conclusively that Mercury orbited around the Sun. [12]

A very rare event in astronomy is the passage of one planet in front of another (occultation), as seen from Earth. In Shia Islam The Occultation is a term used to designate the hidden state of the Imam of the Time. Mercury and Venus occult each other every few centuries, and the event of May 28, 1737 is the only one historically observed, having been seen by John Bevis at the Royal Greenwich Observatory. Events 585 BC - A Solar eclipse occurs as predicted by Greek philosopher and scientist Thales, while Alyattes is battling Year 1737 ( MDCCXXXVII) was a Common year starting on Tuesday (link will display the full calendar of the Gregorian calendar (or a John Bevis ( October 31[[ 693]] or November 10[[ 695]] &ndash November 6, 1771) was an English doctor and Astronomer The Royal Observatory Greenwich (formerly the Royal Greenwich Observatory or RGO) was commissioned in 1675 by King Charles II, with the [78] The next occultation of Mercury by Venus will be on December 3, 2133. Events 1800 - War of the Second Coalition: Battle of Hohenlinden, French The 22nd century of the Common Era will span the years 2101&ndash2200 of the Gregorian calendar. [79]

The difficulties inherent in observing Mercury mean that it has been far less studied than the other planets. In 1800 Johann Schröter made observations of surface features, claiming to observed 20 km high mountains. Johann Hieronymus Schröter ( August 30 1745 &ndash August 29 1816) was a German Astronomer. Friedrich Bessel used Schröter's drawings to erroneously estimate the rotation period as 24 hours and an axial tilt of 70°. Friedrich Wilhelm Bessel (22 July 1784 &ndash 17 March 1846 was a German Mathematician, Astronomer, and systematizer of the Bessel functions [80] In the 1880s Giovanni Schiaparelli mapped the planet more accurately, and suggested that Mercury’s rotational period was 88 days, the same as its orbital period due to tidal locking. Honors and Awards Awards Gold Medal of the Royal Astronomical Society (1872 Bruce Medal (1902 Named A separate article treats the phenomenon of Tidal resonance in Oceanography. [81] This phenomenon is known as synchronous rotation and is also shown by Earth’s Moon. In Astronomy, synchronous rotation is a planetological term describing a body orbiting another where the orbiting body takes as long to rotate The effort to Map the surface of Mercury was continued by Eugenios Antoniadi, who published a book in 1934 that included both maps and his own observations. [47] Many of the planet's surface features, particularly the albedo features, take their names from Antoniadi's map. This is a list of the Albedo features of the planet Mercury as seen by early telescopic observation [82]

Italian astronomer Giuseppe Colombo noted that the rotation value was about two-thirds of Mercury’s orbital period, and proposed that a different form of tidal locking had occurred in which the planet’s orbital and rotational periods were locked into a 3:2 rather than a 1:1 resonance. Giuseppe Colombo ( October 2, 1920  – February 20, 1984) better known by his nickname Bepi Colombo, was an Italian Scientist [89] Data from Mariner 10 subsequently confirmed this view. [90]

Ground-based observations did not shed much further light on the innermost planet, and it was not until space probes visited Mercury that many of its most fundamental properties became known. However, recent technological advances have led to improved ground-based observations. In 2000, high-resolution lucky imaging from the Mount Wilson Observatory 1500 mm telescope provided the first views that resolved some surface features on the parts of Mercury which were not imaged in the Mariner missions. Lucky imaging (also called lucky exposures) is one form of Speckle imaging used for Astronomical photography. The Mount Wilson Observatory (MWO is an Astronomical observatory in Los Angeles County California. [91] Later imaging has shown evidence of a huge double-ringed impact basin even larger than the Caloris Basin in the non-Mariner-imaged hemisphere. The Caloris Basin, also called Caloris Planitia, is an Impact crater on Mercury about 1550 km in Diameter, one of the largest It has informally been dubbed the Skinakas Basin. The Skinakas Basin is the informal name given to a structure on Mercury that appears to be an extremely large Impact basin. [33] Most of the planet has been mapped by the Arecibo radar telescope, with 5 km resolution, including polar deposits in shadowed craters of what may be water ice. [92]

The Mariner 10 probe, the first probe to visit the innermost planet

### Research with space probes

Reaching Mercury from Earth poses significant technical challenges, since the planet orbits so much closer to the Sun than does the Earth. The exploration of Mercury has taken only a minor role in the space interests of the world A Mercury-bound spacecraft launched from Earth must travel over 91 million kilometers into the Sun’s gravitational potential well. A spacecraft is a Vehicle or machine designed for Spaceflight. Gravitation is a natural Phenomenon by which objects with Mass attract one another A potential well is the region surrounding a Local minimum of Potential energy. Starting from the Earth’s orbital speed of 30 km/s, the change in velocity (delta-v) the spacecraft must make to enter into a Hohmann transfer orbit that passes near Mercury is large compared to other planetary missions. The orbital speed of a body generally a Planet, a Natural satellite, an artificial satellite, or a Multiple star, is the speed at which it In Physics, velocity is defined as the rate of change of Position. In Astrodynamics, the term delta-v, literally "change in velocity" (see symbol delta) has a specific meaning it is a Scalar which takes In Astronautics and Aerospace engineering, the Hohmann transfer orbit is an Orbital maneuver using two engine impulses which under standard assumptions [93]

The potential energy liberated by moving down the Sun’s potential well becomes kinetic energy; requiring another large delta-v change to do anything other than rapidly pass by Mercury. Potential energy can be thought of as Energy stored within a physical system A potential well is the region surrounding a Local minimum of Potential energy. The kinetic energy of an object is the extra Energy which it possesses due to its motion In order to land safely or enter a stable orbit the spacecraft must rely entirely on rocket motors since aerobraking is ruled out because the planet has very little atmosphere. Aerobraking is a Spaceflight maneuver that reduces the high point of an Elliptical orbit ( Apoapsis) by flying the vehicle through the Atmosphere A trip to Mercury actually requires more rocket fuel than that required to escape the solar system completely. In Physics, escape velocity is the speed where the Kinetic energy of an object is equal to the magnitude of its Gravitational potential energy As a result, only two space probes have visited the planet so far. [94] A proposed alternative approach would use a solar sail to attain a Mercury-synchronous orbit around the Sun. Solar sails (also called light sails or photon sails, especially when they use Light sources other than the Sun) are a proposed form of [95]

#### Mariner 10

Main article: Mariner 10
View of Mercury from Mariner 10

The first spacecraft to visit Mercury was NASA’s Mariner 10 (1974–75). Mariner 10 was a robotic Space probe launched on November 3, 1973 to fly by the planets Mercury and Venus. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Mariner 10 was a robotic Space probe launched on November 3, 1973 to fly by the planets Mercury and Venus. [10] The spacecraft used the gravity of Venus to adjust its orbital velocity so that it could approach Mercury, making it both the first spacecraft to use this gravitational “slingshot” effect and the first NASA mission to visit multiple planets. The VENUS ( V ictoria E xperimental N etwork U nder the S ea project is a cabled sea floor observatory operated by the University In Orbital mechanics and Aerospace engineering, a gravitational slingshot, gravity assist or swing-by is the use of the relative movement and [93] Mariner 10 provided the first close-up images of Mercury’s surface, which immediately showed its heavily cratered nature, and also revealed many other types of geological features, such as the giant scarps which were later ascribed to the effect of the planet shrinking slightly as its iron core cools. [96] Unfortunately, due to the length of Mariner 10's orbital period, the same face of the planet was lit at each of Mariner 10’s close approaches. This made observation of both sides of the planet impossible,[97] and resulted in the mapping of less than 45% of the planet’s surface. [98]

The spacecraft made three close approaches to Mercury, the closest of which took it to within 327 km of the surface. [99] At the first close approach, instruments detected a magnetic field, to the great surprise of planetary geologists—Mercury’s rotation was expected to be much too slow to generate a significant dynamo effect. A dynamo, originally another name for an Electrical generator, now means a generator that produces Direct current with the use of a commutator. The second close approach was primarily used for imaging, but at the third approach, extensive magnetic data were obtained. The data revealed that the planet’s magnetic field is much like the Earth’s, which deflects the solar wind around the planet. The solar wind is a Stream of charged particles&mdasha plasma &mdashthat are ejected from the upper atmosphere of the Sun. However, the origin of Mercury’s magnetic field is still the subject of several competing theories. [100]

Just a few days after its final close approach, Mariner 10 ran out of fuel. Since its orbit could no longer be accurately controlled, mission controllers instructed the probe to shut itself down on March 24, 1975. Events 1401 - Mongol emperor Timur sacks Damascus. 1603 - James VI of Scotland [101] Mariner 10 is thought to be still orbiting the Sun, passing close to Mercury every few months. [102]

#### MESSENGER

Main article: MESSENGER
MESSENGER being prepared for launch

A second NASA mission to Mercury, named MESSENGER (MErcury Surface, Space ENvironment, GEochemistry, and Ranging), was launched on August 3, 2004, from the Cape Canaveral Air Force Station aboard a Boeing Delta 2 rocket. The MErcury Surface Space ENvironment GEochemistry and Ranging ( MESSENGER) probe is a NASA Spacecraft, launched August 3, 2004 Events 8 - Roman Empire General Tiberius defeats Dalmatians on the river Bathinus. "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " The Cape Canaveral Air Force Station (CCAFS is a detachment of the 45th Space Wing (45 SW Patrick AFB provides headquarters functions from the 45 SW a major airfield The MESSENGER spacecraft will make several close approaches to planets to place it onto the correct trajectory to reach an orbit around Mercury. It made a fly-by of the Earth in August 2005, and of Venus in October 2006 and June 2007. [103] The first fly-by of Mercury occurred on January 14, 2008. Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common [104] Two more fly-bys of Mercury are scheduled, in October 2008 and September 2009. [7] Most of the hemisphere not imaged by Mariner 10 will be mapped during the fly-bys. The probe will then enter an elliptical orbit around the planet in March 2011; the nominal mapping mission is one terrestrial year. [104]

The mission is designed to shed light on six key issues: Mercury’s high density, its geological history, the nature of its magnetic field, the structure of its core, whether it really has ice at its poles, and where its tenuous atmosphere comes from. In Physics, a magnetic field is a Vector field that permeates space and which can exert a magnetic force on moving Electric charges To this end, the probe is carrying imaging devices which will gather much higher resolution images of much more of the planet than Mariner 10, assorted spectrometers to determine abundances of elements in the crust, and magnetometers and devices to measure velocities of charged particles. A spectrometer is an Optical instrument used to measure properties of Light over a specific portion of the Electromagnetic spectrum, typically used A magnetometer is a scientific instrument used to measure the strength and/or direction of the Magnetic field in the vicinity of the instrument Detailed measurements of tiny changes in the probe’s velocity as it orbits will be used to infer details of the planet’s interior structure. [22]

#### BepiColombo

Main article: BepiColombo

The European Space Agency is planning a joint mission with Japan called BepiColombo, which will orbit Mercury with two probes: one to map the planet and the other to study its magnetosphere[105]. BepiColombo is a joint Cornerstone mission of the European Space Agency (ESA and the Japan Aerospace Exploration Agency (JAXA to the planet Mercury The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member For a topic outline on this subject see List of basic Japan topics. BepiColombo is a joint Cornerstone mission of the European Space Agency (ESA and the Japan Aerospace Exploration Agency (JAXA to the planet Mercury A magnetosphere' is a highly magnetized region around and possessed by an Astronomical object. A Russian Soyuz rocket will launch the bus carrying the two probes in 2013 from ESA's Guiana Space Center to take advantage of its equatorial location. Russia (Россия Rossiya) or the Russian Federation ( Rossiyskaya Federatsiya) is a transcontinental Country extending The Soyuz launch vehicle (Western designation A-2 is an Expendable launch system manufactured by TsSKB-Progress in Samara Russia. The Guiana Space Centre, or more commonly Centre Spatial Guyanais (CSG is a French Spaceport near Kourou in French Guiana. [105] As with MESSENGER, the BepiColombo bus will make close approaches to other planets en route to Mercury for orbit-changing gravitational assists, passing the Moon and Venus and making several approaches to Mercury before entering orbit. [105] A combination of chemical and ion engines will be used, the latter thrusting continuously for long intervals. [106][105] The spacecraft bus will reach Mercury in 2019. [106] The bus will release the magnetometer probe into an elliptical orbit, then chemical rockets will fire to deposit the mapper probe into a circular orbit. Both probes will operate for a terrestrial year. [105]

The mapper probe will carry an array of spectrometers similar to those on MESSENGER, and will study the planet at many different wavelengths including infrared, ultraviolet, X-ray and gamma ray. Infrared ( IR) radiation is Electromagnetic radiation whose Wavelength is longer than that of Visible light, but shorter than that of Ultraviolet ( UV) light is Electromagnetic radiation with a Wavelength shorter than that of Visible light, but longer than X-rays X-radiation (composed of X-rays) is a form of Electromagnetic radiation. Gamma rays (denoted as &gamma) are a form of Electromagnetic radiation or light emission of frequencies produced by sub-atomic particle interactions Apart from intensively studying the planet itself, mission planners also hope to use the probe's proximity to the Sun to test the predictions of General Relativity theory with improved accuracy. General relativity or the general theory of relativity is the geometric theory of Gravitation published by Albert Einstein in 1916 [107]

The mission is named after Giuseppe (Bepi) Colombo, the scientist who first determined the nature of Mercury’s spin-orbit resonance and who was also involved in the planning of Mariner 10’s gravity-assisted trajectory to the planet in 1974. Giuseppe Colombo ( October 2, 1920  – February 20, 1984) better known by his nickname Bepi Colombo, was an Italian Scientist [23]

## Notes

1. ^ 1/30 of a degree is the fractional equivalent to 2. 1 arcminutes.
2. ^ Some sources precede the cuniform transcription with "MUL". "MUL" is a cuneiform sign that was used in the Sumerian language to designate a star or planet, but it is not considered part of the actual name. The "4" is a reference number in the Sumero-Akkadian transliteration system to designate which of several syllables a certain cuneiform sign is most likely designating.

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95. ^ Leipold, M. ; Seboldt, W. ; Lingner, S. ; Borg, E. ; Herrmann, A. ; Pabsch, A. ; Wagner, O. ; Bruckner, J. (July 1996). "Mercury sun-synchronous polar orbiter with a solar sail". Acta Astronautica 39 (1): 143–151. doi:10.1016/S0094-5765(96)00131-2. A digital object identifier ( DOI) is a permanent identifier given to an Electronic document.
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97. ^ BepiColumbo - Background Science. European Space Agency. Retrieved on 2008-05-30. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1416 - The Council of Constance, called by the Emperor Sigismund a supporter of Antipope John XXIII burns Jerome of Prague following
98. ^ Tariq Malik. "MESSENGER to test theory of shrinking Mercury", USA Today, August 16, 2004. Events 1384 - The Hongwu Emperor of Ming China, Emperor Dong hears a case of a couple who tore paper money bills while fighting "MMIV" redirects here For the Modest Mouse album see " Baron von Bullshit Rides Again " Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
99. ^ Merton E. Davies, et al (1978). "Mariner 10 Mission and Spacecraft", Atlas of Mercury. NASA Office of Space Sciences. The National Aeronautics and Space Administration ( NASA, ˈnæsə is an agency of the United States government, responsible for the nation's public space program Retrieved on 2008-05-30. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1416 - The Council of Constance, called by the Emperor Sigismund a supporter of Antipope John XXIII burns Jerome of Prague following
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102. ^ Grayzeck, Ed (April 2, 2008). Events 68 - Galba, Governor of Hispania, names himself legatus senatus populique Romani, breaking the line of 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Mariner 10. NSSDC Master Catalog. NASA. Retrieved on 2008-04-07. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 529 - First draft of Corpus Juris Civilis (a fundamental work in Jurisprudence) is issued by Eastern Roman Emperor
103. ^ MESSENGER Engine Burn Puts Spacecraft on Track for Venus. SpaceRef. com (2005). Retrieved on 2006-03-02. Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Events 986 - Louis V becomes King of the Franks. 1127 - Assassination of Charles the Good
104. ^ a b Countdown to MESSENGER's Closest Approach with Mercury. Johns Hopkins University Applied Physics Laboratory (January 14, 2008). Events 1129 - Formal approval of the Order of the Templar at the Council of Troyes. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Retrieved on 2008-05-30. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1416 - The Council of Constance, called by the Emperor Sigismund a supporter of Antipope John XXIII burns Jerome of Prague following
105. ^ a b c d e ESA gives go-ahead to build BepiColombo. European Space Agency (February 26, 2007). The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member Events 747 BC - Epoch (origin of Ptolemy 's Nabonassar Era 364 - Valentinian I is proclaimed Year 2007 ( MMVII) was a Common year starting on Monday of the Gregorian calendar in the 21st century. Retrieved on 2008-05-29. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 363 - Roman Emperor Julian defeats the Sassanid army in the Battle of Ctesiphon, under the walls of the
106. ^ a b Nic Fleming. "Star Trek-style ion engine to fuel Mercury craft", The Telegraph, January 18, 2008. Events 350 - Generallus Magnentius deposes Roman Emperor Constans and proclaims himself Emperor 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Retrieved on 2008-05-23. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 1430 - Siege of Compiègne: Joan of Arc is captured by the Burgundians while leading an army to relieve Compiègne
107. ^ Objectives. European Space Agency (February 21, 2006). The European Space Agency ( ESA) established in 1975 is an intergovernmental organisation dedicated to the exploration of space, currently with 17 member Events 362 - Athanasius returns to Alexandria. 1245 - Thomas, the first known Bishop of Finland Year 2006 ( MMVI) was a Common year starting on Sunday of the Gregorian calendar. Retrieved on 2008-05-29. 2008 ( MMVIII) is the current year in accordance with the Gregorian calendar, a Leap year that started on Tuesday of the Common Events 363 - Roman Emperor Julian defeats the Sassanid army in the Battle of Ctesiphon, under the walls of the