MESSENGER Mission Data Overview

The following notices contains a overview of data which were discovered about Mercury by the MESSENGER mission. Some data from additional and later studies will possibly be added to the texts and mostly pointed to like such

Images and data collected by MESSENGER at Mercury, generally, revealed a unique, geologically diverse world as it is a lot less similar to the Moon than many astronomers previously thought. Mercury may be characterized by main geological features like its surface composition, a widespread volcanism, faults and cliffs and some areas showing a contraction and stretching of the crust. A other, evident, characteristic of Mercury is a dichotomy between two faces, with the one of Caloris Basin more affected by volcanism

• Mercury apparently is very similar to our Moon. Its surface is mainly made of craters of various sizes and ages, of basins, and of lava flows as its general aspect now fully revealed is the one of a planet the relief of which have been toned down or even fattened out. One of Mercury main feature is Caloris Basin, 807 mi (1300) km wide which was created by an impactor larger than 62 mi (100 km). Ejecta were sent up to 600-800 km away. Some plains are less cratered due to lava flows. Mercury soil, like Moon's was progressively covered with regolith produced by micrometeorites striking the surface. Mercury possesses much more iron and titanium, those heavy metals, than thought. The numbers of the metals are similar to what is seen at the Moon's maria, inside the basalts there, providing thus a important step into what was known of Mercury until now. The whole planet, on the other hand, is covered with a light blue material which might be partly iron. That material might have been brought to surface by volcanoes from Mercury's core. The planet's core is estimated to represent 60 percent of the mass total, making Mercury the densest planet in the solar system. Mercury does not show any evidence of iron-bearing silicate minerals. Spectrographic studies have shown that variations in color and reflectance among major terrains at Mercury can fit a varying mix of a material found in 'red' plains, bright, and a dark one which might be iron-titanium oxides. MESSENGER also uncovered that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed polar craters. Presence of ice is due to the tilt of Mercury's rotational axis at almost zero so there are pockets at the planet's poles that never see sunlight. Why some of Mercury’s surface looks new, like the Northern Volcanic Plains as some appears to be old, like intercrater plains and heavily cratered terrains might explained like followed. Mercury is the least oxidized planet of our solar system, where most of its iron is bound to metal or sulfide rather than an oxide. Mercury's building blocks might be enstatite chondrites which are metal-rich and least oxidized, which are also the materials Earth and Moon also built from -- which suggests that much of the inner solar system may have been made from the same material rather than from diverse materials as traditionally believed. A layered structure of the planet's interior is not needed to a heterogeneous composition of the surface because a large variety of melts can be brought to its surface from a wide range of depths: varying pressure and temperature on only one type of composition could produce the surface's heterogeneity. Older terrains thus on Mercury likely formed by material melting deep in the boundary between the core and mantle, while younger terrains formed closer to the surface. At reduced conditions, sulfur dissolves into the silicate mantle and also influences the melting and melt compositions, which is a further explanation to heterogeneity. Whether the mantle of Mercury homogenized through convection early in its history, or was it never layered, why Mercury has a larger core than any other planet, whether a giant impact stripped out some of the mantle are still questions unanswered about the swift planet however
• a important feature is that volcanism has been widespread on the planet with smooth plains -mostly volcanic deposits- occupying at least 40 percent of the surface. Mercury's early history was marked by pervasive volcanism or tectonics which endured several episodes.That suggests the planet spanned a much greater duration volcanism than previously thought, perhaps extending well into the second half of solar system history. Some craters have been seen filled with more than 1-mile deep lava about 3.8 to 4 billion years ago. Some large impact basins have had their interior filled with lava according to a process similar to what occurred at the Moon. Mercury's crust might have been mostly yielded by volcanoes spreading lava, which dried. Such observations tend to show that Mercury be more like Mars than like our Moon. Impact craters have excavated material similar to plains from depths as great as several miles. As some volcanic deposits seem to be the product of explosive eruptions, there is thus a evidence that volatiles exist in Mercury's interior. Explosive volcanic vents are extant too as results of effusive volcanism. The Heavy Bombardment period, further, which occurred 4 billion years ago when the leftovers of the formation of the solar system heavily impacted the newly born planets, might well have stripped Mercury from its original surface. Hence the surface we see nowaday likely not is the original, differentiation-processed crust of Mercury
• a few areas of Mercury ar showing that the planet's crust extended or stretched, like a set of more than 200 narrow troughs radiating from the center of the Caloris impact basin. The contraction of Mercury was found one third greater than previously thought. In a more general way, large faults associated with cliffs are also a record of the global contraction which occurred at Mercury when the planet's interior coolded over eons. Mercury is displaying huge cliffs winding along hundreds of miles (kilometers) across the planet as that is a evidence of a fault activity throughout Mercury's history. Cliffs are the surface expression of large faults. When Mercury's interior cooled and the planet contracted slightly, surface rocks were caused to fracture and some blocks of crust to thrust over others along great faults. Those characteristics of Mercury are suggesting Mercury's history is unlike any of the other rocky planets in the solar system

MESSENGER generally also improved our understanding of Mercury's magnetosphere and gravitational fields as it discovered new constituents of the atmosphere, or demonstrated that Mercury's magnetosphere is more responsive to changes in its environment than at any other planet. The thin Mercury's 'exosphere' (considered 42 percent helium, 42 percent sodium and 15 percent oxygen) is replenished with particles from the surface processes and provides for a long tail of atoms flowing behind the planet as new chemicals like some magnesium, a important constituent of Mercury's surface, have been found. Varied processes are at work to replenish the Mercurian exosphere like the solar wind's photons, or micrometeoroids. Sodium above all, calcium and magnesium vary in quantities which could also be a hint to that the surface of Mercury changed over time, likely leading to the atmosphere being the result of billions of years. The distribution of individual chemical elements also varies in the exosphere, with considerable variability for sodium, calcium, and magnesium. Ionized calcium in Mercury's exosphere is concentrated over a relatively small portion of the exosphere, with most of the emission occurring close to the equatorial plane. It looks like the interaction between those processes and Mercury's magnetosphere is also extant, or a factor. Mercury's exosphere was also found to endure 'seasonal' changes due to the change of the solar pressure along the planet's orbit, with the greatest amount of sodium for example in the exosphere is when Mercury is at a middle distance from the Sun. MESSENGER's first flyby on January 14, 2008, confirmed that the planet has a global magnetic field, as first discovered by the Mariner 10 spacecraft during its flybys of the planet in 1974 and 1975. It is likely due to a core magneto as Mercury's core should contain a light element like sulfur (for that, Mercury would have had to combine elements from close to the Sun and from farther away -an idea known under 'radial mixing'). If not the magnetosphere might be due as well to remnant magnetism emanating from iron-bearing rocks once magnetized by a stronger magnetosphere. The magnetosphere of Mercury is filled with many charged particles forming a 'plasma nebula' akin to Io plasma torus. The proximity of Mercury to the Sun strenghten too the reconnection events occurring between the interplanetary, and planetary magnetic fields. Increases in energy measured in Mercury's magnetic tail are very large, occurring quickly, lasting only two to three minutes from beginning to end, and about 10 times greater than at Earth. Those features might be due to the extreme tail loading and unloading. Like at Earth, some connections may establish between the solar wind and the protective magnetosphere of Mercury, allowing the solar wind to reach down to the surface. At Mercury that takes the form of joined magnetic fields turning into vortex-like tubes, through which the solar wind is entering. This action unto the surface of Mercury is further allowed as Mercury has about no atmosphere. Mercury's own magnetosphere also is interacted with Mercury exosphere's particles and other dynamic forces. Elements from the soil freed by photons of the solar wind can be converted into positive ions, or a process called photoionization. A 'drift belt' might thence exist around Mercury maybe yiedling a magnetic depression in this region

Surface
Volcanism
Crust Contraction and Stretching
Exosphere
Magnetosphere

Surface

MESSENGER produced both a monochrome map at 250 meters per pixel and an eight-color, 1 kilometer per pixel color map as these maps cover the entire planet under uniform lighting conditions. The first-ever precise topographic model of the planet's northern hemisphere on a other hand is showing that the spread in elevations is considerably smaller than those of Mars or the Moon with the most prominent feature a extensive area of lowlands at high northern latitudes that hosts the volcanic northern plains. Within this lowland region is a broad topographic rise that formed after the volcanic plains were emplaced. At mid-latitudes, the interior plains of the Caloris impact basin -960 miles (1,550 km) in diameter- have been modified so that part of the basin floor now stands higher than the rim. The elevated portion appears to be part of a quasi-linear rise that extends for approximately half the planetary circumference at mid-latitudes. These features imply that large-scale changes to Mercury's topography occurred after the era of impact basin formation and large-scale emplacement of volcanic plains had ended. A new digital model for Mercury in 2016 have shown that the highest elevation on the planet is at 2.78 miles (4.48 kilometers) above Mercury’s average elevation, located just south of the equator in some of Mercury’s oldest terrain. The lowest elevation, at 3.34 miles (5.38 kilometers) below Mercury’s average, is found on the floor of Rachmaninoff basin, an intriguing double-ring impact basin suspected to host some of the most recent volcanic deposits on the planet. Northern volcanic plains are due to past volcanic activity which buried this portion of the planet beneath extensive lavas, more than a mile deep in some areas. In terms of Mercury's surface composition, the magnesium/silicon, aluminum/silicon, and calcium/silicon ratios averaged over large areas of the planet's surface show that, unlike the surface of the Moon, Mercury's surface is not dominated by feldspar-rich rocks. Substantial amounts of sulfur also have been observed with sulfide minerals likely present, suggesting that the original building blocks from which Mercury was assembled may have been less oxidized than those that formed the other terrestrial planets, and it has potentially important implications for understanding the nature of volcanism on Mercury. Mercury has a volatile inventory similar to Venus, Earth, and Mars, and much larger than that of the Moon. It possesses a much higher mass fraction of iron metal than Venus, Earth, or Mars as observations hint that Mercury's surface composition is similar to that expected if the planet's bulk composition is broadly similar to that of highly reduced or metal-rich chondritic meteorites, a material that is left over from the formation of the solar system. The first precise model of Mercury's gravity field has been developed which, when combined with topographic data and the planet's spin state, sheds light on the planet's internal structure. Mercury's core represents about 85 percent of the planetary radius, even larger than previous estimates. Despite the planet's small size subtle dynamical motions measured from Earth-based radar, combined with MESSENGER's newly measured parameters of the gravity field and the characteristics of Mercury's internal magnetic field signify an active core dynamo, thus indicating that the planet's core is at least partially liquid

->The Question of Water at Mercury!
Observations by the MESSENGER spacecraft by late 2012 has provided compelling support for the long-held hypothesis that Mercury harbors abundant water ice and other frozen volatile materials in its permanently shadowed polar craters. Spectrometer, reflectance and temperature models are part of the evidence. Presence of ice is due to the tilt of Mercury's rotational axis at almost zero so there are pockets at the planet's poles that never see sunlight. In 1991, the Arecibo radio telescope in Puerto Rico alreazdy had detected unusually radar-bright patches at Mercury's poles, spots that reflected radio waves in the way one would expect if there were water ice. Many of these patches corresponded to the location of large impact craters mapped by the Mariner 10 spacecraft in the 1970s'. But because Mariner saw less than 50 percent of the planet, planetary scientists lacked a complete diagram of the poles to compare with the images. Astronomers, from such recent results, think that ice at Mercury is buried beneath an unusually dark material across most of the deposits. A hydrogen-rich layer which could be water ice, more than tens of inches (centimeters) thick is extant beneath a thermally insulating superficial layer 10 to 20 inches (centimeters) thick. Ice and the insulating layer at Mercury likely was deposited by impacts of comets or asteroids. The dark material is likely a mix of complex organic compounds and may have been darkened further by exposure to the harsh radiation at Mercury's surface, even in permanently shadowed areas

	A global color map of Mercury's surface has been created by mosaicking thousands of sets of images obtained by the MESSENGER Wide Angle Camera (WAC). The colors shown here are related to variations in the spectral reflectance across the planet. This view captures both compositional differences and differences in how long materials have been exposed at Mercury's surface. Young crater rays, arrayed radially around fresh impact craters, appear light blue or white. Medium- and dark-blue areas are a geologic unit of Mercury's crust known as the 'low-reflectance material,' thought to be rich in a dark, opaque mineral. Tan areas are plains formed by eruption of highly fluid lavas. The large circular area near the top center is the Caloris impact basin, whose interior is filled with smooth, somewhat younger volcanic plains. Small orangish spots are materials deposited by explosive volcanic eruptions. As material is exposed to the harsh space environment around Mercury it darkens, generally. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	During the second of its three scheduled passages at Mercury, in October 2008, NASA's MESSENGER helped unveiled a whole hemisphere of Mercury which was unknown until now! The only striking discovery, on the other hand, consisted of the view that the hemisphere is completely striated by longitudinal rays which emanate from a northern crater!. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	A comparison of the internal structures of Earth and Mercury as currently understood based on the latest data from the MESSENGER mission. Mercury’s interior has a larger ratio of metallic core material to silicate rock material than the Earth. Mercury also appears to have a solid layer of iron sulfide that lies at the top of the core. The presence of this solid layer places important constraints on the temperatures within Mercury’s interior and may influence the generation of the planet’s magnetic field. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	Major-element composition of Mercury surface materials as a comparison with the inner solar system planets Venus excepted. picture courtesy NASA
	A striking boundary of smooth and rough terrain near Mercury's north pole which comes after crossing the expansive northern plains. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	The upper part of this view of Mercury's surface includes a swath of material that has reflectance that does not strongly increase toward longer wavelengths, a property described as relatively "blue" in color. The bluish material also has lower overall reflectance than Mercury's average surface. The terrain to the South and West has a more reddish color. A major puzzle of Mercury's geology is the identity of the particular rock types that correspond to these colors (the area is the one of craters Amaral, Neruda and Sher-Gil). picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	Maps of magnesium/silicon (left) and thermal neutron absorption (right) across Mercury’s surface (red indicates high values, blue low) are shown with volcanic smooth plains deposits outlined in white. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Volcanism

Importance of volcanism in the formation of Mercurian plains is larger than expected. Broad expanses of plains across the planet already seen by the Mariner 10 mission likely were formed through volcanism, which played a important role in shaping Mercury's crust. MESSENGER data show how volcanic rocks dominate much of Mercury's crust, even in regions that are geologically complex and where impact cratering has destroyed many of the original surface features. Lavas are locally as thick as 1.2 miles (2 kilometers) as they flooded plains, craters and low-lying plains, as vents, measuring up to 16 miles (25 kilometers) appear to be the source of some of the tremendous lava flows. Lava flows also eroded the substrate, carving valleys and creating teardrop-shaped ridges. Mercury, on the other hand, lacks of iron in the silicate minerals of the surface rocks, which is a main difference to most planetery crusts known until now. Sulfur is present. Data have revealed that bright, patchy deposits on some crater floors already observed but unexplained are clusters of rimless, irregular pits often surrounded by diffuse halos of higher-reflectance material, and they are found associated with central peaks, peak rings, and rims of craters. They might be young and hinting to a more abundant than expected volatile component in Mercury's crust. 'Hollows' at last, or very bright and blue small, shallow, irregularly shaped depressions that are often found in clusters on craters floor and central mountain peaks, are a variety of pits which still could be actively forming today thus a active Mercury! A possible relationship is thought to exist between the formation of explosive volcanic deposits and hollows

	Many regions of Mercury's surface are comprised of relatively red and smooth terrain that appears to flood low-lying regions and partially fill or bury older craters. These smooth plains are thought to have been formed by volcanic activity that drowned the region in voluminous, low-viscosity lavas. . picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	That rimless, non-circular depression lies along the inner margin of the Caloris basin. It is the vent of a small, explosive volcano, similar to other volcanic vents on Mercury! The small number of superposed craters indicates that this feature is relatively young. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	A pit seen inside Picasso crater is hypothesized to be a location where subsurface magma has evacuated, causing the surface to cave in. Such pits have been seen in various locations around Mercury too. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	A hummocky, pitted texture which could relate to past volcanic activity, and several troughs are visible in the center of crater Derain. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	The irregularly shaped 19-mile (30-km)-diameter pit in the large crater at the bottom of that picture is thought to be related to shallow volcanic activity and to have formed due to the withdrawal of near-surface magma, causing the overlying surface to collapse. Such craters with interior volcanic pits are known as pit-floor craters. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	Lessing crater can be seen in the lower left of this image and, instead of the typical central peak found in a complex crater on Mercury it sports a central pit, likely formed by volcanic activity. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	MESSENGER has discovered a unexpected class of shallow, irregular depressions (yellow arrows). Some of the depressions have bright interiors and halos (white arrows). The science team is referring to these features as "hollows" in order to distinguish them from other types of non-impact depressions found on Mercury like volcanic vents, or collapse pits. The origin of hollows is not certain, but may involve loss of volatile material, like the sublimation of material when exposed by a impact which created a crater. picture courtesy AAAS/Science
	The central peaks of Eminescu Crater are revealed here at high resolution, showing off a remarkable view of hollows! Some of those have coalesced into larger formations. A fine Mercurian horizon also is seen in the background. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	Hollows have been now found a relatively common feature on Mercury. Their sharp walls and well-defined features stand out against the muted background terrain, indicating they are substantially younger than their surroundings as that might hint too to that they are still forming today. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Crust Contraction and Stretching

MESSENGER found unusual groups of ridges and troughs on Mercury, which are assemblages of tectonic landforms. Unlike faulting which is due to contraction of Mercury when it colded only, such features are linked to horizontal stretching and pulling apart of crustal material. Families of extensional troughs, or graben, encircled by contractional wrinkle ridges arranged in circular rings have been observed, for example at Mercurian basins. They are also associated with ghost craters which are impact craters that have been flooded and buried by lava flows. The thin volcanic deposits overlying the rim of a fully buried impact crater serve to concentrate contractional forces, leading to the formation of a ridge ring that reveals the outline of the buried crater. The process at work combines eruption and rapid accumulation of very fluid lava flows into thick cooling units and Mercury high rate of global contraction, hence a characteristic seen at Mercury only. Small scarps associated with small troughs of only tens of yards (meters) wide are geologically young, which means Mercury is still geologically active due to its contraction. A 'great valley' in Mercury southern hemisphere's Rembrandt basin as discovered by 2016, is providing more evidence that the small planet closest to the Sun is shrinking. Cooling of Mercury’s interior caused the planet’s single outer crust plate to contract and bend

	Beagle Rupes, the arcuate ridge seen in this picture, is one of the tallest and longest scarps on Mercury and seen in July 2011. It is seen deforming and shortening the elliptical impact crater Sveinsdóttir in the bottom left corner of the image. Beagle Rupes and other scarps on Mercury are thought to be the surface expressions of thrust faults that formed from contraction as the planet's interior cooled. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	Large Rembrandt basin is seen left as in contrast to the relatively darker material surrounding Rembrandt, Amaral crater and its bright rays can be seen on the right. Rembrandt basin is an area of particular scientific interest due to its large size, young age, and extensional and contractional characteristics. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington
	A portion of the 73-mile (116-km) wide Abedin crater is showing many small troughs that are interpreted to be graben, a result of extensional stresses which may have resulted from the cooling and solidification of either impact melt or volcanic fill. picture courtesy NASA/Johns Hopkins University Applied Physics Laboratory/Carnegie Institution of Washington

Exosphere

Mercury tenuous exosphere of gas is generated and maintained by the interaction of the space environment with the planet's surface as some discrepancies about how much magnesium and calcium are found on the night side might question the usual thought that those were knocked out from the day side and brought into the night side by the solar wind pressure. The real explanation why magnesium and calcium in the exosphere are higher in quantity at Mercury’s dawn, is that that is due to meteoroid impacts are more frequent there. That is due further to that Mercury's day is long, at 58 Earth days exposing the planet at 'retrograde meteoroids,' which orbit the Sun in the direction opposite the planets

Magnetosphere

Discoveries related to Mercury's interior brought a evolution of knowledge relative to how Mercury's magnetic field is generated and for understanding how the planet evolved thermally. Orbital data reveal that Mercury's magnetic field is offset far to the North of the planet's center, by nearly 20 percent of Mercury's radius. Relative to the planet's size, this offset is much more than in any other planet, and accounting for it will pose a challenge to theoretical explanations of the field. This means also that the magnetic field in the southern hemisphere should be a lot weaker than it is in the North, with a difference of 3.5 times. Hence energetic particles, solar wind, and high-energy electrons will preferentially impact the surface in the South and a assymetry of the exosphere's particles and too the decolouration of those by charged particles. Also scientists have observed a unexplained enhanced concentration of calcium at the equator near dawn, a pattern that appears to be a persistent feature in the exosphere as such dawn enhancements are not observed for magnesium, albeit chemically similar to calcium. Sodium is the most important ion concentrated near Mercury's poles as likely liberated by solar wind in a manner comparable to which auroras are generated at Earth. Someone standing on Mercury's nightside at the right time of year would see a faint orange glow, the light of the planet's sodium tail. Helium is also found in the entire volume of the magnetosphere as delivered from the Sun by the solar wind. Such a weak magnetosphere provides the planet very little protection from the solar wind and extreme space weather must be a continuing activity at the surface of the planet closest to the Sun. Energetic events made of burst of energetic particles are being seen almost like clockwork in Mercury Earth-like magnetosphere. Such bursts had been one of the major discoveries made by the Mariner 10 mission as it was puzzling that MESSENGER had not detected any during its three flybys

	Magnetic field lines differ at Mercury's north and south poles. picture courtesy NASA
	Locations of energetic electron events relative to Mercury’s magnetic field. picture courtesy NASA