Mercury's magnetic field
Mercurys magnetic field is approximately a magnetic dipole apparently global, on planet Mercury. Data from Mariner 10 led to its discovery in 1974, the spacecraft measured the strength as 1. 1% that of Earths magnetic field. The origin of the field can be explained by dynamo theory. The magnetic field is strong enough near the bow shock to slow the solar wind, the magnetic field is about 1. 1% as strong as Earths. At the Hermean equator, the strength of the magnetic field is around 300 nT. Mercurys magnetic field is weaker than Earths because its core had cooled and solidified more quickly than Earths, although Mercurys magnetic field is much weaker than Earths magnetic field, it is still strong enough to deflect the solar wind, inducing a magnetosphere. Whether the magnetic field changed to any significant degree between the Mariner 10 mission and the MESSENGER mission remains an open question, in addition they pointed out that estimates of the dipole obtained from bow shock and/or magnetopause positions range from approximately 200 nT-RM3 to approximately 400 nT-RM3.
They concluded that the lack of agreement among models is due to limitations imposed by the spatial distribution of available observations. 2011, using high-quality MESSENGER data from many orbits around Mercury – as opposed to just a few high-speed flybys – found that the moment is 195 ±10 nT-RM3. The origins of the field can be explained by dynamo theory. Before the discovery of its field in 1974, it was thought that because of Mercury′s small size. There are still difficulties with this theory, including the fact that Mercury has a slow. This dynamo is probably weaker than Earths because it is driven by thermo-compositional convection associated with inner core solidification, because of the planets slow rotation, the resulting magnetic field is dominated by small-scale components that fluctuate quickly with time. Like Earths, Mercurys magnetic field is tilted, meaning that the poles are not located in the same area as the geographic poles. As a result of the asymmetry in Mercurys internal magnetic field.
In particular, the polar cap where field lines are open to the interplanetary medium is much larger near the south pole. This geometry implies that the polar region is much more exposed than in the north to charged particles heated and accelerated by solar wind–magnetosphere interactions. The strength of the moment and the tilt of the dipole moment are completely unconstrained
Discovery Rupes is an escarpment on Mercury approximately 650 kilometers long and 2 kilometers high, located at latitude 56.3 S and longitude 38.3 W. It was formed by a thrust fault, thought to have occurred due to the shrinkage of the core as it cooled over time. The scarp cuts through Rameau crater and it was discovered by Mariner 10 Discovery Rupes Discovery Region, Mercury
The Tolstoj quadrangle in the equatorial region of Mercury runs from 144 to 216° longitude and -25 to 25° latitude. It was provisionally called Tir, but renamed after Leo Tolstoy by the International Astronomical Union in 1976 and it contains the southern part of Caloris Planitia, which is the largest and best preserved basin seen by Mariner 10. This basin, about 1550 km in diameter, is surrounded by a discontinuous annulus of ejecta deposits of the Caloris Group that are embayed and covered by broad expanses of smooth plains. The ancient and degraded Tolstoj multiring basin, about 350 km in diameter, is in the part of the quadrangle. The “hot pole” at 180° lies within the Tolstoj quadrangle, at perihelion and this daily range of 600 K is greater than that on any other body in the solar system. Mariner 10 photographic coverage was available for only the eastern two-thirds of the Tolstoj quadrangle, image data from three Mariner 10 encounters with Mercury were used in mapping the quadrangle.
The rolling to hummocky plains that lie between large craters in the part of the quadrangle make up the oldest recognizable map unit. Malin showed the plains to contain highly eroded remnants of large craters, superposition of crater ejecta over parts of intercrater plains in other areas indicates that some large craters formed in a preexisting intercrater plains unit. On the other hand, the plains material partly postdates some of the major cratering events on Mercury. A complex history of contemporaneous craters and plains formation is therefore suggested, a detailed discussion of the origin of the intercrater plains on the Moon and Mercury was given by Strom. Patches of less cratered, less rolling plains occur throughout the quadrangle, because their distribution cannot now be mapped accurately, many of these patches are included with the smooth plains material. Certain patches of these plains, where clearly rougher and possibly older, are mapped as the intermediate plains material. The impact that produced the Tolstoj Basin occurred very early in the history of the quadrangle, diffuse patches of material of dark albedo lie outside the innermost ring.
The central part of the basin is covered by smooth plains material, the ejecta tends to be blocky and only weakly lineated between the inner and outer rings. Radial lineations with a slight swirly pattern are best seen on the southwest side of Tolstoj, analysis of stereo- photography of Tolstoj ejecta northeast of the crater suggests that this deposit has been upwarped to a higher elevation relative to the surrounding plains. The Caloris Basin is especially significant from a stratigraphic standpoint, like the Imbrium and Orientale Basins on the Moon, it is surrounded by an extensive and well-preserved ejecta blanket. As on the Moon, where ejecta from the better preserved basins was used to construct a stratigraphy and this ejecta is recognizable to a distance of about one basin diameter in the Tolstoj quadrangle and the adjacent Shakespeare quadrangle to the north. Undoubtedly, the ejecta influences a large part of the terrain to the west
Impact craters and basins, their numerous secondary craters, and heavily to lightly cratered plains are the characteristic landforms of the region. At least six multiringed basins ranging from 150 km to 440 km in diameter are present, Mercury I includes 75 whole-frame photographs of the Kuiper quadrangle, Mercury II,13 whole-frame photographs, and Mercury III,70 quarter-frame photographs. The photographs include 19 stereopairs in the part of the quadrangle. The most distant of the photographs was taken at an altitude of 89,879 km, therefore, varies widely but ranges from about 1.5 to 2.0 km over most of the area. A wide range of viewing and solar illumination angles precludes a high degree of mapping consistency. The easternmost 10° of the quadrangle is beyond the evening terminator, a low angle of solar illumination and a high viewing angle make possible discrimination of topographic detail near the terminator. Higher angles of illumination and lower viewing angles make it increasingly difficult to discern topographic variations to the west.
Many geologic units cannot be identified because of unfavourable viewing geometry west of approximately 55 deg. Mapping methods and principles are adapted from those developed for lunar photogeologic mapping, a photomosaic map of the best available photographs aided greatly in geologic interpretation and mapping. The rock units are subdivided into three groups, plains materials, terra materials, and crater and basin materials. The oldest rocks exposed in the quadrangle are the plains material. Collectively, these form a relatively subdued terrain of moderate relief. They are similar to some of the rolling and hilly terra and hilly and pitted materials in the lunar highlands, particularly in the Purbach. The intercrater plains unit is marked by the soft outlines of numerous overlapping secondary craters producing a subdued hummocky texture. Much of its surface is covered by a relatively thick regolith of reworked impact breccias. The cratered plains material is relatively flat with broad ridges and lobate scarps that in places resemble those of some of the lunar maria and it is difficult to obtain reliable crater counts on this unit because many secondary craters cannot be distinguished from primary craters.
Cratered plains materials embay craters in classes c1 to c3, they may represent lava flows extruded after an initial phase ofimpact flux. The albedo of the plains is intermediate compared to that of other mercurian units, but higher than that of the lunar maria
The Victoria quadrangle is a region on Mercury from 0 to 90° longitude and 20 to 70 ° latitude. It is designated the H-2 quadrangle, and is known as Aurora after a large albedo feature. As is common with most of the portions of Mercury. At the time the pictures were obtained, the terminator was at about long 7° to 8°, a large gap in coverage between the incoming and outgoing images appears as a northeast-trending diagonal blank strip on the base map. A small part of this gap was filled in the part of the quadrangle by very poor second-encounter images. No images provide a view, in fact, the smallest angle between the planetary surface normal and the camera axis is about 50°. The high obliquity of the images, the range in sun-elevation angles. Only in about 15 percent of the quadrangle, near the southeast corner, three widespread units are recognized within the Victoria quadrangle. These are, from oldest to youngest, intercrater plains material, intermediate plains material, in addition, central peak, floor and ejecta materials related to the numerous craters and basins larger than about 20 km in diameter are mapped.
About half of the area consists of material characterized by a very high density of small, mostly degraded craters. Superposition relations suggest that this unit is about the age as, or older than, all mappable craters. Some of the more plainslike areas included within this unit may well have a similar to that of intermediate plains material. Within the 5° overlap area with the Kuiper quadrangle to the south, an area has been mapped that displays moderately rough to rough terrain and this unit is very similar to intercrater plains material, and cannot be distinguished from it anywhere else in the Victoria quadrangle. Most of the plains material is probably volcanic in origin. Smooth to moderately irregular plains occupy most of the area between large craters not underlain by intercrater plains material and these plains superficially resemble the plains of the lunar maria, they generally have a relatively low albedo and are characterized by numerous elongate ridges. Like the lunar maria, the two younger mercurian plains units have been ascribed to volcanic activity, although this interpretation has been questioned, a volcanic origin seems most probable, but no compelling evidence exists in the Victoria quadrangle to support this opinion.
The elongate ridges, though associated with intermediate plains material, are not restricted to it. Partly filling most craters is plains material that is smoother and less cratered than intermediate plains material
In geometry, a diameter of a circle is any straight line segment that passes through the center of the circle and whose endpoints lie on the circle. It can be defined as the longest chord of the circle, both definitions are valid for the diameter of a sphere. In more modern usage, the length of a diameter is called the diameter. In this sense one speaks of the rather than a diameter, because all diameters of a circle or sphere have the same length. Both quantities can be calculated efficiently using rotating calipers, for a curve of constant width such as the Reuleaux triangle, the width and diameter are the same because all such pairs of parallel tangent lines have the same distance. For an ellipse, the terminology is different. A diameter of an ellipse is any chord passing through the midpoint of the ellipse, for example, conjugate diameters have the property that a tangent line to the ellipse at the endpoint of one of them is parallel to the other one. The longest diameter is called the major axis, the word diameter is derived from Greek διάμετρος, diameter of a circle, from διά, through and μέτρον, measure.
It is often abbreviated DIA, dia, d, or ⌀, the definitions given above are only valid for circles and convex shapes. However, they are cases of a more general definition that is valid for any kind of n-dimensional convex or non-convex object. The diameter of a subset of a space is the least upper bound of the set of all distances between pairs of points in the subset. So, if A is the subset, the diameter is sup, if the distance function d is viewed here as having codomain R, this implies that the diameter of the empty set equals −∞. Some authors prefer to treat the empty set as a case, assigning it a diameter equal to 0. For any solid object or set of scattered points in n-dimensional Euclidean space, in medical parlance concerning a lesion or in geology concerning a rock, the diameter of an object is the supremum of the set of all distances between pairs of points in the object. In differential geometry, the diameter is an important global Riemannian invariant, the symbol or variable for diameter, ⌀, is similar in size and design to ø, the Latin small letter o with stroke.
In Unicode it is defined as U+2300 ⌀ Diameter sign, on an Apple Macintosh, the diameter symbol can be entered via the character palette, where it can be found in the Technical Symbols category. The character will not display correctly, since many fonts do not include it. In many situations the letter ø is a substitute, which in Unicode is U+00F8 ø
Beagle Rupes is an escarpment on Mercury, one of the highest and longest yet seen. It was discovered in 2008 when MESSENGER made its first flyby of the planet and it has an arcuate shape and is about 600 km long. The scarp is a manifestation of a thrust fault, which formed when the planet contracted as its interior cooled. Beagle Rupes consists of three segments, the central segment trends in the north–south direction and crosscuts the elliptically shaped Sveinsdóttir crater. The dimensions of the latter are 220 ×120 km, the floor of Sveinsdóttir was flooded by the smooth plains material and deformed by wrinkle-ridges before the appearance of Beagle Rupes. The maximum relief within the crater is about 0.8 km, to the south of Sveinsdóttir the scarp turns to the south–east. A27 km diameter crater is superposed on this segment, to the north of Sveinsdóttir the scarp turns to north–east completing a large arc. This segment of Beagle Rupes crosscuts and deforms a small 17 km diameter crater, the relief in this places reaches 1.5 km.
The scarp appears to be a feature, which postdates the emplacement of the smooth plans. Beagle Rupes is named after HMS Beagle, a ship made famous through association with Charles Darwin
Atmosphere of Mercury
Mercury has a very tenuous and highly variable atmosphere containing hydrogen, oxygen, calcium and water vapor, with a combined pressure level of about 10−14 bar. The exospheric species originate either from the Solar wind or from the planetary crust, Solar light pushes the atmospheric gases away from the Sun, creating a comet-like tail behind the planet. The existence of a Mercurian atmosphere had been contentious before 1974, although by that time a consensus had formed that Mercury, like the Moon and this conclusion was confirmed in 1974 when the unmanned Mariner 10 spaceprobe discovered only a tenuous exosphere. Later, in 2008, improved measurements were obtained by the MESSENGER spacecraft, the Mercurian exosphere consists of a variety of species originating either from the Solar wind or from the planetary crust. The first constituents discovered were atomic hydrogen and atomic oxygen, the near-surface concentrations of these elements were estimated to vary from 230 cm−3 for hydrogen to 44,000 cm−3 for oxygen, with an intermediate concentration of helium.
In 2008 the MESSENGER probe confirmed the presence of atomic hydrogen, Mercurys exospheric hydrogen and helium are believed to come from the Solar wind, while the oxygen is likely to be of crustal origin. The fourth species detected in Mercurys exosphere was sodium and it was discovered in 1985 by Drew Potter and Tom Morgan, who observed its Fraunhofer emission lines at 589 and 589.6 nm. The average column density of this element is about 1 ×1011 cm−2, sodium is observed to concentrate near the poles, forming bright spots. Its abundance is enhanced near the dawn terminator as compared to the dusk terminator, some research has claimed a correlation of the sodium abundance with certain surface features such as Caloris or radio bright spots, however these results remain controversial. The properties and spatial distribution of two elements are otherwise very similar. In 1998 another element, was detected with column density three orders of magnitude below that of sodium, observations by the MESSENGER probe in 2009 showed that calcium is concentrated mainly near the equator—opposite to what is observed for sodium and potassium.
In 2008 the MESSENGER probes Fast Imaging Plasma Spectrometer discovered several molecular and different ions in the vicinity of Mercury, including H2O+ and their abundances relative to sodium are about 0.2 and 0.7, respectively. Other ions such as H3O+, OH, O2+ and Si+ are present as well, the near-surface abundance of this newly detected constituent is roughly comparable to that of sodium. Mariner 10s ultraviolet observations have established an upper bound on the surface density at about 105 particles per cubic centimeter. This corresponds to a pressure of less than 10−14 bar. The temperature of the Mercurys exosphere depends on species as well as geographical location, for exospheric atomic hydrogen, the temperature appears to be about 420 K, a value obtained by both Mariner 10 and MESSENGER. The temperature for sodium is much higher, reaching 750–1500 K on the equator and 1, some observations show that Mercury is surrounded by a hot corona of calcium atoms with temperature between 12,000 and 20,000 K.
Because of Mercurys proximity to the Sun, the pressure of light is much stronger than near Earth
Caloris Planitia is a plain within a large impact basin on Mercury, informally named Caloris, about 1,550 km in diameter. It is one of the largest impact basins in the Solar System, calor is Latin for heat and the basin is so-named because the Sun is almost directly overhead every second time Mercury passes perihelion. The crater, discovered in 1974, is surrounded by a ring of mountains approximately 2 km tall, Caloris was discovered on images taken by the Mariner 10 probe in 1974. It was situated on the line dividing the daytime and nighttime hemispheres—at the time the probe passed by. Later, on January 15,2008, one of the first photos of the planet taken by the MESSENGER probe revealed the crater in its entirety. The basin was estimated to be about 810 mi in diameter. It is ringed by mountains up to 2 km high, inside the crater walls, the floor of the crater is filled by lava plains, similar to the maria of the Moon. These plains are superposed by explosive vents associated with pyroclastic material, outside the walls, material ejected in the impact which created the basin extends for 1,000 km, and concentric rings surround the crater.
In the center of the basin is a region containing numerous radial troughs that appear to be extensional faults, the exact cause of this pattern of troughs is not currently known. The feature is named Pantheon Fossae, the impacting body is estimated to have been at least 100 km in diameter. Bodies in the inner Solar System experienced a heavy bombardment of large bodies in the first billion years or so of the Solar System. Based on MESSENGERs photographs, Caloris age has been determined to be between 3.8 and 3.9 billion years, the giant impact believed to have formed Caloris may have had global consequences for the planet. At the exact antipode of the basin is an area of hilly, grooved terrain. It is thought by some to have created as seismic waves from the impact converged on the opposite side of the planet. Alternatively, it has suggested that this terrain formed as a result of the convergence of ejecta at this basin’s antipode. This hypothetical impact is believed to have triggered volcanic activity on Mercury.
Surrounding Caloris is a series of geologic formations thought to have produced by the basins ejecta. Mercury has a tenuous and transient atmosphere, containing small amounts of hydrogen and helium captured from the solar wind
Mercury is the smallest and innermost planet in the Solar System. Its orbital period around the Sun of 88 days is the shortest of all the planets in the Solar System and it is named after the Roman deity Mercury, the messenger to the gods. Like Venus, Mercury orbits the Sun within Earths orbit as a planet, so it can only be seen visually in the morning or the evening sky. Also, like Venus and the Moon, the displays the complete range of phases as it moves around its orbit relative to Earth. Seen from Earth, this cycle of phases reoccurs approximately every 116 days, although Mercury can appear as a bright star-like object when viewed from Earth, its proximity to the Sun often makes it more difficult to see than Venus. Mercury is tidally or gravitationally locked with the Sun in a 3,2 resonance, as seen relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun. As seen from the Sun, in a frame of reference that rotates with the orbital motion, an observer on Mercury would therefore see only one day every two years.
Mercurys axis has the smallest tilt of any of the Solar Systems planets, at aphelion, Mercury is about 1.5 times as far from the Sun as it is at perihelion. Mercurys surface appears heavily cratered and is similar in appearance to the Moons, the polar regions are constantly below 180 K. The planet has no natural satellites. Mercury is one of four planets in the Solar System. It is the smallest planet in the Solar System, with a radius of 2,439.7 kilometres. Mercury is smaller—albeit more massive—than the largest natural satellites in the Solar System, Mercury consists of approximately 70% metallic and 30% silicate material. Mercurys density is the second highest in the Solar System at 5.427 g/cm3, Mercurys density can be used to infer details of its inner structure. Although Earths high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller, for it to have such a high density, its core must be large and rich in iron. Geologists estimate that Mercurys core occupies about 55% of its volume, Research published in 2007 suggests that Mercury has a molten core.
Surrounding the core is a 500–700 km mantle consisting of silicates, based on data from the Mariner 10 mission and Earth-based observation, Mercurys crust is estimated to be 35 km thick. One distinctive feature of Mercurys surface is the presence of narrow ridges