Pit-floor Crater
   HOME

TheInfoList



OR:

The geology of Mercury is the scientific study of the surface, crust, and interior of the planet
Mercury Mercury commonly refers to: * Mercury (planet), the nearest planet to the Sun * Mercury (element), a metallic chemical element with the symbol Hg * Mercury (mythology), a Roman god Mercury or The Mercury may also refer to: Companies * Merc ...
. It emphasizes the composition, structure, history, and physical processes that shape the planet. It is analogous to the field of terrestrial
geology Geology () is a branch of natural science concerned with Earth and other astronomical objects, the features or rocks of which it is composed, and the processes by which they change over time. Modern geology significantly overlaps all other Ear ...
. In
planetary science Planetary science (or more rarely, planetology) is the scientific study of planets (including Earth), celestial bodies (such as moons, asteroids, comets) and planetary systems (in particular those of the Solar System) and the processes of their f ...
, the term ''geology'' is used in its broadest sense to mean the study of the solid parts of planets and moons. The term incorporates aspects of
geophysics Geophysics () is a subject of natural science concerned with the physical processes and physical properties of the Earth and its surrounding space environment, and the use of quantitative methods for their analysis. The term ''geophysics'' som ...
,
geochemistry Geochemistry is the science that uses the tools and principles of chemistry to explain the mechanisms behind major geological systems such as the Earth's crust and its oceans. The realm of geochemistry extends beyond the Earth, encompassing the e ...
,
mineralogy Mineralogy is a subject of geology specializing in the scientific study of the chemistry, crystal structure, and physical (including optical) properties of minerals and mineralized artifacts. Specific studies within mineralogy include the proces ...
,
geodesy Geodesy ( ) is the Earth science of accurately measuring and understanding Earth's figure (geometric shape and size), orientation in space, and gravity. The field also incorporates studies of how these properties change over time and equivale ...
, and
cartography Cartography (; from grc, χάρτης , "papyrus, sheet of paper, map"; and , "write") is the study and practice of making and using maps. Combining science, aesthetics and technique, cartography builds on the premise that reality (or an im ...
. Historically, Mercury has been the least understood of all the
terrestrial planets A terrestrial planet, telluric planet, or rocky planet, is a planet that is composed primarily of silicate rocks or metals. Within the Solar System, the terrestrial planets accepted by the IAU are the inner planets closest to the Sun: Mercury, Ven ...
in the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
. This stems largely from its proximity to the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
which makes reaching it with spacecraft technically challenging and Earth-based observations difficult. For decades, the principal source of geologic information about Mercury came from the 2,700 images taken by the
Mariner 10 ''Mariner 10'' was an American Robotic spacecraft, robotic space probe launched by NASA on 3 November 1973, to fly by the planets Mercury (planet), Mercury and Venus. It was the first spacecraft to perform flybys of multiple planets. ''Ma ...
spacecraft during three flybys of the planet from 1974 to 1975. These images covered about 45% of the planet’s surface, but many of them were unsuitable for detailed geologic investigation because of high sun angles which made it hard to determine surface morphology and
topography Topography is the study of the forms and features of land surfaces. The topography of an area may refer to the land forms and features themselves, or a description or depiction in maps. Topography is a field of geoscience and planetary sci ...
. Strom, R.G. in “Geology of the Terrestrial Planets,” M.H. Carr, Ed., Special Paper 469, NASA Scientific and Technical Information Branch:Washington D.C., 1984, p. 13. https://www.lpi.usra.edu/publications/books/geologyTerraPlanets/ This dearth of information was greatly alleviated by the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (
MESSENGER ''MESSENGER'' was a NASA robotic space probe that orbited the planet Mercury between 2011 and 2015, studying Mercury's chemical composition, geology, and magnetic field. The name is a backronym for "Mercury Surface, Space Environment, Geoche ...
) spacecraft which between 2008 and 2015 collected over 291,000 images MESSENGER website. Johns Hopkins Applied Physics Laboratory. https://messenger.jhuapl.edu/Explore/images/impressions/messenger-byTheNumbers-lg.jpg covering the entire planet, along with a wealth of other scientific data.
The European Space Agency , owners = , headquarters = Paris, Île-de-France, France , coordinates = , spaceport = Guiana Space Centre , seal = File:ESA emblem seal.png , seal_size = 130px , image = Views in the Main Control Room (1205 ...
’s (ESA’s)
BepiColumbo BepiColombo is a joint mission of the European Space Agency (ESA) and the Japan Aerospace Exploration Agency (JAXA) to the planet Mercury. The mission comprises two satellites launched together: the Mercury Planetary Orbiter (MPO) and ''Mio'' ( ...
spacecraft, scheduled to go into orbit around Mercury in 2025, is expected to help answer many of the remaining questions about Mercury’s geology. Mercury's surface is dominated by
impact craters An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
, basaltic rock and smooth plains, many of them a result of flood volcanism, similar in some respects to the
lunar maria The lunar maria (; singular: mare ) are large, dark, basaltic plains on Earth's Moon, formed by ancient asteroid impacts on the far side on the Moon that triggered volcanic activity on the opposite (near) side. They were dubbed , Latin for 'seas' ...
, and locally by pyroclastic deposits. Other notable features include
vents Vent or vents may refer to: Science and technology Biology *Vent, the cloaca region of an animal *Vent DNA polymerase, a thermostable DNA polymerase Geology *Hydrothermal vent, a fissure in a planet's surface from which geothermally heated water ...
which appear to be the source of magma-carved valleys, often-grouped irregular-shaped depressions termed "hollows" that are believed to be the result of collapsed magma chambers, scarps indicative of thrust faulting and mineral deposits (possibly ice) inside craters at the poles. Long thought to be geologically inactive, new evidence suggests there may still be some level of activity. Mercury's density implies a solid iron-rich core that accounts for about 60% of its volume (75% of its radius). Mercury's magnetic equator is shifted nearly 20% of the planet's radius towards the north, the largest ratio of all planets. This shift suggests there being one or more iron-rich molten layers surrounding the core producing a dynamo effect similar to that of Earth. Additionally, the offset magnetic
dipole In physics, a dipole () is an electromagnetic phenomenon which occurs in two ways: *An electric dipole deals with the separation of the positive and negative electric charges found in any electromagnetic system. A simple example of this system i ...
may result in uneven surface weathering by the
solar wind The solar wind is a stream of charged particles released from the upper atmosphere of the Sun, called the corona. This plasma mostly consists of electrons, protons and alpha particles with kinetic energy between . The composition of the sola ...
, knocking more surface particles up into the southern
exosphere The exosphere ( grc, ἔξω "outside, external, beyond", grc, σφαῖρα "sphere") is a thin, atmosphere-like volume surrounding a planet or natural satellite where molecules are gravitationally bound to that body, but where the densit ...
and transporting them for deposit in the north. Scientists are gathering
telemetry Telemetry is the in situ data collection, collection of measurements or other data at remote points and their automatic data transmission, transmission to receiving equipment (telecommunication) for monitoring. The word is derived from the Gr ...
to determine if such is the case. After having completed the first
solar day A synodic day (or synodic rotation period or solar day) is the period for a celestial object to rotate once in relation to the star it is orbiting, and is the basis of solar time. The synodic day is distinguished from the sidereal day, which is ...
of its mission in September 2011, more than 99% of Mercury's surface had been mapped by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
's ''
MESSENGER ''MESSENGER'' was a NASA robotic space probe that orbited the planet Mercury between 2011 and 2015, studying Mercury's chemical composition, geology, and magnetic field. The name is a backronym for "Mercury Surface, Space Environment, Geoche ...
'' probe in both color and monochrome with such detail that scientists' understanding of Mercury's geology has significantly surpassed the level achieved following the ''
Mariner 10 ''Mariner 10'' was an American Robotic spacecraft, robotic space probe launched by NASA on 3 November 1973, to fly by the planets Mercury (planet), Mercury and Venus. It was the first spacecraft to perform flybys of multiple planets. ''Ma ...
'' flybys of the 1970s.


Difficulties in exploration

Reaching Mercury from Earth poses significant technical challenges, because the planet orbits so much closer to the Sun than does the Earth. A Mercury-bound
spacecraft A spacecraft is a vehicle or machine designed to fly in outer space. A type of artificial satellite, spacecraft are used for a variety of purposes, including communications, Earth observation, meteorology, navigation, space colonization, p ...
launched from Earth must travel 91 million kilometers into the Sun's
gravitational In physics, gravity () is a fundamental interaction which causes mutual attraction between all things with mass or energy. Gravity is, by far, the weakest of the four fundamental interactions, approximately 1038 times weaker than the strong ...
potential well A potential well is the region surrounding a local minimum of potential energy. Energy captured in a potential well is unable to convert to another type of energy (kinetic energy in the case of a gravitational potential well) because it is captur ...
. Starting from the Earth's
orbital speed In gravitationally bound systems, the orbital speed of an astronomical body or object (e.g. planet, moon, artificial satellite, spacecraft, or star) is the speed at which it orbits around either the barycenter or, if one body is much more massi ...
of 30 km/s, the change in
velocity Velocity is the directional speed of an object in motion as an indication of its rate of change in position as observed from a particular frame of reference and as measured by a particular standard of time (e.g. northbound). Velocity is a ...
(
delta-v Delta-''v'' (more known as "change in velocity"), symbolized as ∆''v'' and pronounced ''delta-vee'', as used in spacecraft flight dynamics, is a measure of the impulse per unit of spacecraft mass that is needed to perform a maneuver such as ...
) the spacecraft must make to enter into a
Hohmann transfer orbit In astronautics, the Hohmann transfer orbit () is an orbital maneuver used to transfer a spacecraft between two orbits of different altitudes around a central body. Examples would be used for travel between low Earth orbit and the Moon, or ano ...
that passes near Mercury is large compared to other planetary missions. The
potential energy In physics, potential energy is the energy held by an object because of its position relative to other objects, stresses within itself, its electric charge, or other factors. Common types of potential energy include the gravitational potentia ...
liberated by moving down the Sun's potential well becomes
kinetic energy In physics, the kinetic energy of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. Having gained this energy during its accele ...
; requiring another large delta-''v'' to do anything other than rapidly pass by Mercury. In order to land safely or enter a stable orbit the spacecraft must rely entirely on rocket motors because Mercury has negligible atmosphere. A direct trip to Mercury actually requires more rocket fuel than that required to
escape Escape or Escaping may refer to: Computing * Escape character, in computing and telecommunication, a character which signifies that what follows takes an alternative interpretation ** Escape sequence, a series of characters used to trigger some so ...
the Solar System completely. As a result, only two space probes, ''
Mariner 10 ''Mariner 10'' was an American Robotic spacecraft, robotic space probe launched by NASA on 3 November 1973, to fly by the planets Mercury (planet), Mercury and Venus. It was the first spacecraft to perform flybys of multiple planets. ''Ma ...
'' and ''
MESSENGER ''MESSENGER'' was a NASA robotic space probe that orbited the planet Mercury between 2011 and 2015, studying Mercury's chemical composition, geology, and magnetic field. The name is a backronym for "Mercury Surface, Space Environment, Geoche ...
'', both by
NASA The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research. NASA was established in 1958, succeeding t ...
, have visited Mercury so far. Furthermore, the space environment near Mercury is demanding, posing the double dangers to spacecraft of intense
solar radiation Solar irradiance is the power per unit area (surface power density) received from the Sun in the form of electromagnetic radiation in the wavelength range of the measuring instrument. Solar irradiance is measured in watts per square metre (W/m ...
and high temperatures. Historically, a second obstacle has been that Mercury's period of rotation is a slow 58
Earth Earth is the third planet from the Sun and the only astronomical object known to harbor life. While large volumes of water can be found throughout the Solar System, only Earth sustains liquid surface water. About 71% of Earth's surfa ...
days, so that spacecraft flybys are restricted to viewing only a single illuminated hemisphere. In fact, unfortunately, even though
Mariner 10 ''Mariner 10'' was an American Robotic spacecraft, robotic space probe launched by NASA on 3 November 1973, to fly by the planets Mercury (planet), Mercury and Venus. It was the first spacecraft to perform flybys of multiple planets. ''Ma ...
space probe flew past Mercury three times during 1974 and 1975, it observed the same area during each pass. This was because Mariner 10's orbital period was almost exactly 3 sidereal Mercury days, and the same face of the planet was lit at each of the close approaches. As a result, less than 45% of the planet's surface was mapped. Earth-based observations are made difficult by Mercury's constant proximity to the Sun. This has several consequences: #Whenever the sky is dark enough for viewing through telescopes, Mercury is always already near the horizon, where viewing conditions are poor anyway due to atmospheric factors. #The
Hubble Space Telescope The Hubble Space Telescope (often referred to as HST or Hubble) is a space telescope that was launched into low Earth orbit in 1990 and remains in operation. It was not the first space telescope, but it is one of the largest and most versa ...
and other space observatories are usually prevented from pointing close to the Sun for safety reasons (Erroneously pointing such sensitive instruments at the Sun is likely to cause permanent damage).


Mercury's geological history

Like the Earth, Moon and
Mars Mars is the fourth planet from the Sun and the second-smallest planet in the Solar System, only being larger than Mercury (planet), Mercury. In the English language, Mars is named for the Mars (mythology), Roman god of war. Mars is a terr ...
, Mercury's geologic history is divided up into
eras Eras is a humanist sans-serif typeface designed by Albert Boton and Albert Hollenstein and was released by the International Typeface Corporation (ITC) in 1976. Eras is licensed by the Linotype type foundry. A distinct and curious feature of E ...
. From oldest to youngest, these are: the
pre-Tolstojan Pre-Tolstojan, also Pretolstojan Period, refers to the oldest period of the history of Mercury, 4500–3900 MYA. It is the "first period of the Eomercurian Era and of the Mercurian Eon, as well as being the first period in Mercury's geologic h ...
, Tolstojan, Calorian, Mansurian, and Kuiperian. These ages are based on
relative dating Relative dating is the science of determining the relative order of past events (i.e., the age of an object in comparison to another), without necessarily determining their absolute age (i.e., estimated age). In geology, rock or superficial dep ...
only. After the formation of Mercury along with the rest of the
Solar System The Solar SystemCapitalization of the name varies. The International Astronomical Union, the authoritative body regarding astronomical nomenclature, specifies capitalizing the names of all individual astronomical objects but uses mixed "Solar S ...
4.6 billion years ago, heavy bombardment by asteroids and comets ensued. The last intense bombardment phase, the
Late Heavy Bombardment The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypoth ...
came to an end about 3.8 billion years ago. Some regions or
massif In geology, a massif ( or ) is a section of a planet's crust that is demarcated by faults or flexures. In the movement of the crust, a massif tends to retain its internal structure while being displaced as a whole. The term also refers to a ...
s, a prominent one being the one that formed the
Caloris Basin Caloris Planitia is a plain within a large impact basin on Mercury, informally named Caloris, about 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 ...
, were filled by magma eruptions from within the planet. These created smooth intercrater plains similar to the
maria Maria may refer to: People * Mary, mother of Jesus * Maria (given name), a popular given name in many languages Place names Extraterrestrial * 170 Maria, a Main belt S-type asteroid discovered in 1877 * Lunar maria (plural of ''mare''), large, ...
found on the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
. Later, as the planet cooled and contracted, its surface began to crack and form ridges; these surface cracks and ridges can be seen on top of other features, such as the craters and smoother plains—a clear indication that they are more recent. Mercury's period of
volcanism Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called ...
ended when the planet's mantle had contracted enough to prevent further
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
from breaking through to the surface. This probably occurred at some point during its first 700 or 800 million years of history. Since then, the main surface processes have been intermittent impacts.


Timeline

ImageSize = width:780 height:100 PlotArea = left:10 right:10 bottom:20 top:0 AlignBars = early Period = from:-4500 till:0 TimeAxis = orientation:horizontal ScaleMajor = unit:year increment:500 start:-4500 ScaleMinor = unit:year increment:100 start:-4500 LineData= at:-3875 frompos:46 tillpos:55 width:0.5 color:black at:-3825 frompos:13 tillpos:20 width:0.5 color:black PlotData= align:center textcolor:black fontsize:8 mark:(line,black) width:25 shift:(0,-5) text:Mansurian/Kuiperian from:-3000 till:0 color:limegreen text:Late_Calorian from:-3800 till:-3000 color:yellowgreen text:Calorian from:-3850 till:-3800 shift:(5,-30) color:teal text:Tolstojan from:-3900 till:-3850 shift:(0,25) color:brightgreen text:pre-Tolstojan from:start till:-3900 color:green Time unit: millions of years


Surface features

Mercury's surface is overall similar in appearance to that of the Moon, with extensive
mare A mare is an adult female horse or other equine. In most cases, a mare is a female horse over the age of three, and a filly is a female horse three and younger. In Thoroughbred horse racing, a mare is defined as a female horse more than four ...
-like plains and heavily cratered
terrain Terrain or relief (also topographical relief) involves the vertical and horizontal dimensions of land surface. The term bathymetry is used to describe underwater relief, while hypsometry studies terrain relative to sea level. The Latin word ...
s similar to the
lunar highlands The geology of the Moon (sometimes called selenology, although the latter term can refer more generally to "lunar science") is quite different from that of Earth. The Moon lacks a true Celestial body atmosphere, atmosphere, which eliminates erosio ...
and made locally by accumulations of pyroclastic deposits.


Impact basins and craters

Craters on Mercury range in diameter from small bowl-shaped craters to multi-ringed
impact basin An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
s hundreds of kilometers across. They appear in all states of degradation, from relatively fresh rayed-craters, to highly degraded crater remnants. Mercurian craters differ subtly from Lunar craters – the extent of their ejecta blankets is much smaller, which is a consequence of the 2.5 times stronger surface gravity on Mercury. The largest known crater is the enormous
Caloris Basin Caloris Planitia is a plain within a large impact basin on Mercury, informally named Caloris, about 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 ...
, with a diameter of 1,550 km, A basin of comparable size, tentatively named Skinakas Basin had been postulated from low resolution Earth-based observations of the non-Mariner-imaged hemisphere, but has not been observed in ''MESSENGER'' imagery of the corresponding terrain. The impact which created the Caloris Basin was so powerful that its effects are seen on a global scale. It caused
lava Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or un ...
eruptions and left a concentric ring over 2 km tall surrounding the
impact crater An impact crater is a circular depression in the surface of a solid astronomical object formed by the hypervelocity impact of a smaller object. In contrast to volcanic craters, which result from explosion or internal collapse, impact craters ...
. At the antipode of the Caloris Basin lies a large region of unusual, hilly and furrowed terrain, sometimes called "Weird Terrain". The favoured hypothesis for the origin of this geomorphologic unit is that shock waves generated during the impact traveled around the planet, and when they converged at the basin's antipode (180 degrees away) the high stresses were capable of fracturing the surface. A much less favoured idea was that this terrain formed as a result of the convergence of ejecta at this basin's antipode. Furthermore, the formation of the Caloris Basin appears to have produced a shallow depression concentric around the basin, which was later filled by the smooth plains (see below). 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.
Beethoven Basin Beethoven is a crater at latitude 20°S, longitude 124°W on Mercury. It is 630 km in diameter and was named after Ludwig van Beethoven. It is the eleventh largest named impact crater in the Solar System and the third largest on Mercury ...
also has a similar-sized ejecta blanket and a 625 km diameter rim. As on the
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
, fresh craters on Mercury show prominent bright
ray system A ray system comprises radial streaks of fine '' ejecta'' thrown out during the formation of an impact crater, looking somewhat like many thin spokes coming from the hub of a wheel. The rays may extend for lengths up to several times the diameter ...
s. These are made by ejected debris, which tend to be brighter while they remain relatively fresh because of a lesser amount of
space weathering Space weathering is the type of weathering that occurs to any object exposed to the harsh environment of outer space. Bodies without atmospheres (including the Moon, Mercury, the asteroids, comets, and most of the moons of other planets) take on m ...
than the surrounding older terrain.


Pit-floor craters

Some impact craters on Mercury have non-circular, irregularly shaped depressions or pits on their floors. Such craters have been termed pit-floor craters, and ''
MESSENGER ''MESSENGER'' was a NASA robotic space probe that orbited the planet Mercury between 2011 and 2015, studying Mercury's chemical composition, geology, and magnetic field. The name is a backronym for "Mercury Surface, Space Environment, Geoche ...
'' team members have suggested that such pits formed by the collapse of subsurface
magma chamber A magma chamber is a large pool of liquid rock beneath the surface of the Earth. The molten rock, or magma, in such a chamber is less dense than the surrounding country rock, which produces buoyant forces on the magma that tend to drive it upw ...
s. If this suggestion is correct, the pits are evidence of
volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...
processes at work on Mercury. Pit craters are rimless, often irregularly shaped, and steep-sided, and they display no associated
ejecta Ejecta (from the Latin: "things thrown out", singular ejectum) are particles ejected from an area. In volcanology, in particular, the term refers to particles including pyroclastic materials (tephra) that came out of a volcanic explosion and magma ...
or
lava flow Lava is molten or partially molten rock (magma) that has been expelled from the interior of a terrestrial planet (such as Earth) or a moon onto its surface. Lava may be erupted at a volcano or through a fracture in the crust, on land or und ...
s but are typically distinctive in color. For example, the pits of
Praxiteles Praxiteles (; el, Πραξιτέλης) of Athens, the son of Cephisodotus the Elder, was the most renowned of the Attica sculptors of the 4th century BC. He was the first to sculpt the nude female form in a life-size statue. While no indubita ...
have an orange hue. Thought to be evidence of shallow magmatic activity, pit craters may have formed when subsurface magma drained elsewhere and left a roof area unsupported, leading to collapse and the formation of the pit. Major craters exhibiting these features include Beckett, Gibran and
Lermontov Mikhail Yuryevich Lermontov (; russian: Михаи́л Ю́рьевич Ле́рмонтов, p=mʲɪxɐˈil ˈjurʲjɪvʲɪtɕ ˈlʲɛrməntəf; – ) was a Russian Romantic writer, poet and painter, sometimes called "the poet of the Caucas ...
, among others. It was suggested that these pits with associated brighter and redder deposits may be pyroclastic deposits caused by explosive volcanism.


Plains

There are two geologically distinct plains units on Mercury: * '' Intercrater plains'' are the oldest visible surface, predating the heavily cratered terrain. They are gently rolling or hilly and occur in the regions between larger craters. The intercrater plains appear to have obliterated many earlier craters, and show a general paucity of smaller craters below about 30 km in diameter. It is not clear whether they are of volcanic or impact origin. The intercrater plains are distributed roughly uniformly over the entire surface of the planet. * ''Smooth plains'' are widespread flat areas resembling the lunar maria, which fill depressions of various sizes. Notably, they fill a wide ring surrounding the Caloris Basin. An appreciable difference to the lunar maria is that the smooth plains of Mercury have the same albedo as the older intercrater plains. Despite a lack of unequivocally volcanic features, their localisation and lobate-shaped colour units strongly support a volcanic origin. 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. The floor of the
Caloris Basin Caloris Planitia is a plain within a large impact basin on Mercury, informally named Caloris, about 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 also filled by a geologically distinct flat plain, broken up by ridges and fractures in a roughly polygonal pattern. It is not clear whether they are volcanic lavas induced by the impact, or a large sheet of
impact melt Impact may refer to: * Impact (mechanics), a high force or shock (mechanics) over a short time period * Impact, Texas, a town in Taylor County, Texas, US Science and technology * Impact crater, a meteor crater caused by an impact event * Impac ...
.


Tectonic features

One unusual feature of the planet's surface is the numerous compression folds which crisscross the plains. 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. Mercury's surface is also flexed by significant
tidal bulge The tidal force is a gravitational effect that stretches a body along the line towards the center of mass of another body due to a gradient (difference in strength) in gravitational field from the other body; it is responsible for diverse phenomen ...
s raised by the
Sun The Sun is the star at the center of the Solar System. It is a nearly perfect ball of hot plasma, heated to incandescence by nuclear fusion reactions in its core. The Sun radiates this energy mainly as light, ultraviolet, and infrared radi ...
—the Sun's tides on Mercury are about 17% stronger than the Moon's on Earth.


Terminology

Non-crater surface features are given the following names: *
Albedo Albedo (; ) is the measure of the diffuse reflection of sunlight, solar radiation out of the total solar radiation and measured on a scale from 0, corresponding to a black body that absorbs all incident radiation, to 1, corresponding to a body ...
features – areas of markedly different reflectivity *
Dorsa Standard anatomical terms of location are used to unambiguously describe the anatomy of animals, including humans. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...
ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...
s (''see List of ridges on Mercury'') * Montes —
mountain A mountain is an elevated portion of the Earth's crust, generally with steep sides that show significant exposed bedrock. Although definitions vary, a mountain may differ from a plateau in having a limited Summit (topography), summit area, and ...
s (''see List of mountains on Mercury'') *
Planitia In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands. ...
e —
plain In geography, a plain is a flat expanse of land that generally does not change much in elevation, and is primarily treeless. Plains occur as lowlands along valleys or at the base of mountains, as coastal plains, and as plateaus or uplands ...
s (''see List of plains on Mercury'') *
Rupes Rupes (plural ) is the Latin word for 'cliff'. It is used in planetary geology to refer to escarpments on other worlds. , the IAU has named 62 such features in the Solar System, on Mercury (17), Venus (7), the Moon (8), Mars (23), the asteroids V ...
scarps (''see List of scarps on Mercury'') * Valles
valley A valley is an elongated low area often running between Hill, hills or Mountain, mountains, which will typically contain a river or stream running from one end to the other. Most valleys are formed by erosion of the land surface by rivers ...
s (''see List of valleys on Mercury'')


High-albedo polar patches and possible presence of ice

The first radar observations of Mercury were carried out by the
radiotelescope A radio telescope is a specialized antenna and radio receiver used to detect radio waves from astronomical radio sources in the sky. Radio telescopes are the main observing instrument used in radio astronomy, which studies the radio frequency po ...
s at
Arecibo Arecibo (; ) is a city and municipality on the northern coast of Puerto Rico, on the shores of the Atlantic Ocean, located north of Utuado and Ciales; east of Hatillo; and west of Barceloneta and Florida. It is about west of San Juan, the ...
(
Puerto Rico Puerto Rico (; abbreviated PR; tnq, Boriken, ''Borinquen''), officially the Commonwealth of Puerto Rico ( es, link=yes, Estado Libre Asociado de Puerto Rico, lit=Free Associated State of Puerto Rico), is a Caribbean island and Unincorporated ...
) and Goldstone (
California California is a U.S. state, state in the Western United States, located along the West Coast of the United States, Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the List of states and territori ...
, United States), with assistance from the U.S.
National Radio Astronomy Observatory The National Radio Astronomy Observatory (NRAO) is a federally funded research and development center of the United States National Science Foundation operated under cooperative agreement by Associated Universities, Inc. for the purpose of radio a ...
Very Large Array The Karl G. Jansky Very Large Array (VLA) is a centimeter-wavelength radio astronomy observatory located in central New Mexico on the Plains of San Agustin, between the towns of Magdalena and Datil, ~ west of Socorro. The VLA comprises twen ...
(VLA) facility in
New Mexico ) , population_demonym = New Mexican ( es, Neomexicano, Neomejicano, Nuevo Mexicano) , seat = Santa Fe , LargestCity = Albuquerque , LargestMetro = Tiguex , OfficialLang = None , Languages = English, Spanish ( New Mexican), Navajo, Ker ...
. The transmissions sent from the NASA
Deep Space Network The NASA Deep Space Network (DSN) is a worldwide Telecommunications network, network of American spacecraft communication ground segment facilities, located in the United States (California), Spain (Madrid), and Australia (Canberra), that suppo ...
site at Goldstone were at a power level of 460 kW at 8.51 GHz; the signals received by the VLA multi-dish array detected points of radar reflectivity (radar luminosity) with depolarized waves from Mercury's north pole. Radar maps of the surface of the planet were made using the Arecibo radiotelescope. The survey was conducted with 420 kW UHF band (2.4 GHz) radio waves which allowed for a 15 km resolution. This study not only confirmed the existence of the zones of high reflectivity and depolarization, but also found a number of new areas (bringing the total to 20) and was even able to survey the poles. It has been postulated that surface
ice Ice is water frozen into a solid state, typically forming at or below temperatures of 0 degrees Celsius or Depending on the presence of impurities such as particles of soil or bubbles of air, it can appear transparent or a more or less opaq ...
may be responsible for these high luminosity levels, as the silicate rocks that compose most of the surface of Mercury have exactly the opposite effect on luminosity. In spite of its proximity to the Sun, Mercury may have surface ice, since temperatures near the poles are constantly below freezing point: On the polar plains, the temperature does not rise above −106 °C. And
crater Crater may refer to: Landforms *Impact crater, a depression caused by two celestial bodies impacting each other, such as a meteorite hitting a planet *Explosion crater, a hole formed in the ground produced by an explosion near or below the surfac ...
s at Mercury's higher latitudes (discovered by radar surveys from Earth as well) may be deep enough to shield the ice from direct sunlight. Inside the craters, where there is no solar light, temperatures fall to −171 °C. Despite sublimation into the vacuum of space, the temperature in the permanently shadowed region is so low that this sublimation is slow enough to potentially preserve deposited ice for billions of years. At the South Pole, the location of a large zone of high reflectivity coincides with the location of the Chao Meng-Fu crater, and other small craters containing reflective areas have also been identified. At the North Pole, a number of craters smaller than Chao-Meng Fu have these reflective properties. The strength of the radar reflections seen on Mercury are small compared to that which would occur with pure ice. This may be due to powder deposition that does not cover the surface of the crater completely or other causes, e.g. a thin overlying surface layer. However, the evidence for ice on Mercury is not definitive. The anomalous reflective properties could also be due to the existence of deposits of
metal A metal (from Greek μέταλλον ''métallon'', "mine, quarry, metal") is a material that, when freshly prepared, polished, or fractured, shows a lustrous appearance, and conducts electricity and heat relatively well. Metals are typicall ...
lic
sulfates The sulfate or sulphate ion is a polyatomic A polyatomic ion, also known as a molecular ion, is a covalent bonded set of two or more atoms, or of a metal complex, that can be considered to behave as a single unit and that has a net charge t ...
or other materials with high reflectance.


Possible origin of ice

Mercury is not unique in having craters that stand in permanent shadow; at the south pole of Earth's
Moon The Moon is Earth's only natural satellite. It is the fifth largest satellite in the Solar System and the largest and most massive relative to its parent planet, with a diameter about one-quarter that of Earth (comparable to the width of ...
there is a large crater ( Aitken) where some possible signs of the presence of ice have been seen (although their interpretation is disputed). It is thought by astronomers that ice on both Mercury and the Moon must have originated from external sources, mostly impacting
comet A comet is an icy, small Solar System body that, when passing close to the Sun, warms and begins to release gases, a process that is called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. These phenomena ar ...
s. These are known to contain large amounts, or a majority, of ice. It is therefore conceivable for meteorite impacts to have deposited water in the permanently shadow craters, where it would remain unwarmed for possibly billions of years due to the lack of an atmosphere to efficiently conduct heat and stable orientation of Mercury's
rotation axis Rotation around a fixed axis is a special case of rotational motion. The fixed-axis hypothesis excludes the possibility of an axis changing its orientation and cannot describe such phenomena as wobbling or precession. According to Euler's rot ...
.


Mercury's biological history


Habitability

There may be scientific support, based on studies reported in March 2020, for considering that parts of the planet Mercury may have been
habitable Habitability refers to the adequacy of an environment for human living. Where housing is concerned, there are generally local ordinances which define habitability. If a residence complies with those laws it is said to be habitable. In extreme e ...
, and perhaps that
life form Life form (also spelled life-form or lifeform) is an entity that is living, such as plants (flora) and animals (fauna). It is estimated that more than 99% of all species that ever existed on Earth, amounting to over five billion species, are ext ...
s, albeit likely primitive
microorganism A microorganism, or microbe,, ''mikros'', "small") and ''organism'' from the el, ὀργανισμός, ''organismós'', "organism"). It is usually written as a single word but is sometimes hyphenated (''micro-organism''), especially in olde ...
s, may have existed on the planet.


See also

* * *


References

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


Original references for Spanish article

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


External links


''Mariner 10''''MESSENGER'' probe
Retrieved 5 August 2007 {{Planetary Geology