Mercury's surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. Because knowledge of Mercury's geology had been based only on the 1975 flyby and terrestrial observations, it is the least understood of the terrestrial planets. As data from "MESSENGER" orbiter are processed, this knowledge will increase. For example, an unusual crater with radiating troughs has been discovered that scientists called "the spider". It was later named Apollodorus. Albedo features are areas of markedly different reflectivity, as seen by telescopic observation. Mercury has dorsa (also called "wrinkle-ridges"), Moon-like highlands, montes (mountains), planitiae (plains), rupes (escarpments), and valles (valleys).
Surface geology
Mercury (planet)
Mercury (planet) | Surface geology
Mercury has dorsa (also called "wrinkle-ridges"), Moon-like highlands, montes (mountains), planitiae (plains), rupes (escarpments), and valles (valleys). It may appear as a bright star-like object, but is often far more difficult to observe than Venus. It may appear as a bright star-like object, but is often far more difficult to observe. Its surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years.
where is sedna located in the solar system
user
In the outer reaches of the Solar System.
assistant
who discovered it?
user
Michael Brown (Caltech), Chad Trujillo (Gemini Observatory), and David Rabinowitz (Yale University).
assistant
who gave it it's name?
user
Michael Brown.
assistant
what does it look like?
user
It is a large planetoid, surface is redd.
assistant
the system mentioned above, what does it consist of?
user
Sun, the giant planets, four terrestrial planets, the dwarf planets, moons, asteroids, and comets.
assistant
the first thing mentioned, does it have any religious inclusion?
user
Yes, the Sun was worshipped as the god Ra, personified as the goddess.
assistant
which religion did they worship him as the above?
user
Proto-Indo-European religion,  ancient Greek religion, ancient Sumerians.
assistant
does the ancient religion have any concepts of after death revival?
user
They believed in an underworld where the spirits of the dead went after death ,also embraced the idea of reincarnation.
assistant
what is the smallest planet in the system mentioned earlier?
user
Mercury.
assistant
how does this planet look?
user
Mercury's surface is similar in appearance to that of the Moon, showing extensive mare-like plains and heavy cratering, indicating that it has been geologically inactive for billions of years. Because knowledge of Mercury's geology had been based only on the 1975 flyby and terrestrial observations, it is the least understood of the terrestrial planets. As data from "MESSENGER" orbiter are processed, this knowledge will increase. For example, an unusual crater with radiating troughs has been discovered that scientists called "the spider". It was later named Apollodorus. Albedo features are areas of markedly different reflectivity, as seen by telescopic observation. Mercury has dorsa (also called "wrinkle-ridges"), Moon-like highlands, montes (mountains), planitiae (plains), rupes (escarpments), and valles (valleys).
Mercury (planet) | Surface geology
Mercury appears to have a solid silicate crust and mantle overlying a solid, iron sulfide outer core layer, a deeper liquid core layer, and a solid inner core. Mercury is one of four terrestrial planets in the Solar System, and is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of . Mercury is also smaller—albeit more massive—than the largest natural satellites in the Solar System, Ganymede and Titan. Mercury consists of approximately 70% metallic and 30% silicate material. Mercury's density is the second highest in the Solar System at 5.427 g/cm, only slightly less than Earth's density of 5.515 g/cm.
Mercury (planet) | Internal structure
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 bulges raised by the Sun—the Sun's tides on Mercury are about 17% stronger than the Moon's on Earth.
Geology of Mercury | Tectonic features
Mercury ( from the Sun) is the closest planet to the Sun and on average, all seven other planets. The smallest planet in the Solar System (), Mercury has no natural satellites. Besides impact craters, its only known geological features are lobed ridges or rupes that were probably produced by a period of contraction early in its history. Mercury's very tenuous atmosphere consists of atoms blasted off its surface by the solar wind. Its relatively large iron core and thin mantle have not yet been adequately explained. Hypotheses include that its outer layers were stripped off by a giant impact, or that it was prevented from fully accreting by the young Sun's energy.
Solar System | Mercury
One unusual feature of Mercury's surface is the numerous compression folds, or rupes, that crisscross the plains. As Mercury's interior cooled, it contracted and its surface began to deform, creating wrinkle ridges and lobate scarps associated with thrust faults. The scarps can reach lengths of 1000 km and heights of 3 km. These compressional features can be seen on top of other features, such as craters and smooth plains, indicating they are more recent. Mapping of the features has suggested a total shrinkage of Mercury's radius in the range of ~1 to 7 km. Small-scale thrust fault scarps have been found, tens of meters in height and with lengths in the range of a few km, that appear to be less than 50 million years old, indicating that compression of the interior and consequent surface geological activity continue to the present.
Mercury (planet) | Compressional features
Mercury's surface is overall similar in appearance to that of the Moon, with extensive mare-like plains and heavily cratered terrains similar to the lunar highlands and made locally by accumulations of pyroclastic deposits.
Geology of Mercury | Surface features
The geology of Mercury is the least understood of all the terrestrial planets in the Solar System. This stems largely from Mercury's proximity to the Sun which makes reaching it with spacecraft technically challenging and Earth-based observations difficult. Mercury's surface is dominated by impact craters, basaltic rock and smooth plains, many of them a result of flood volcanism, similar in some respects to the lunar maria, and locally by pyroclastic deposits. Other notable features include vents 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.
Geology of Mercury | Introduction
No unequivocal volcanic features, such as flow lobes, leveed channels, domes, or cones are visible. Crater densities indicate that the smooth plains are significantly younger than ejecta from the Caloris basin. In addition, distinct color units, some of lobate shape, are observed in newly processed color data. Such relations strongly support a volcanic origin for the mercurian smooth plains, even in the absence of diagnostic landforms.
Geology of solar terrestrial planets | Mercury
The Mariner 10 mission (1974) mapped about half the surface of Mercury. On the basis of that data, scientists have a first-order understanding of the geology and history of the planet. Mercury's surface shows intercrater plains, basins, smooth plains, craters, and tectonic features. Mercury's oldest surface is its intercrater plains, which are present (but much less extensive) on the Moon. The intercrater plains are level to gently rolling terrain that occur between and around large craters. The plains predate the heavily cratered terrain, and have obliterated many of the early craters and basins of Mercury; they probably formed by widespread volcanism early in mercurian history.
Geology of solar terrestrial planets | Mercury
Names for features on Mercury come from a variety of sources. Names coming from people are limited to the deceased. Craters are named for artists, musicians, painters, and authors who have made outstanding or fundamental contributions to their field. Ridges, or dorsa, are named for scientists who have contributed to the study of Mercury. Depressions or fossae are named for works of architecture. Montes are named for the word "hot" in a variety of languages. Plains or planitiae are named for Mercury in various languages. Escarpments or rupēs are named for ships of scientific expeditions. Valleys or valles are named for abandoned cities, towns, or settlements of antiquity.
Mercury (planet) | Surface geology
Mercury is the smallest and innermost planet in the Solar System. Its orbit around the Sun takes 87.97 days, the shortest of all the planets in the Solar System. It is named after the Greek god Hermes (Ερμής), translated into Latin Mercurius Mercury, god of commerce, messenger of the gods, mediator between gods and mortals. Like Venus, Mercury orbits the Sun within Earth's orbit as an inferior planet, and its apparent distance from the Sun as viewed from Earth never exceeds 28°. This proximity to the Sun means the planet can only be seen near the western horizon after sunset or eastern horizon before sunrise, usually in twilight.
Mercury (planet) | Introduction
Inter-crater plains on Mercury are a land-form consisting of plains between craters on Mercury. Of the eight planets in the solar system, Mercury is the smallest and closest to the Sun. The surface of this planet is similar to the Moon in that it shows characteristics of heavy cratering and plains formed through volcanic eruptions on the surface. These features indicate that Mercury has been geologically inactive for billions of years. Knowledge of Mercury's geology was initially quite limited because observations have only been through the "Mariner 10" flyby in 1975 and observations from Earth. The "MESSENGER" (an acronym of MErcury Surface, Space ENvironment, GEochemistry, and Ranging) mission of 2004 was a robotic NASA spacecraft orbiting the planet, the first spacecraft ever to do so.
Inter-crater plains on Mercury | Introduction
The floor of the Caloris basin is deformed by sinuous ridges and fractures, giving the basin fill a grossly polygonal pattern. These plains may be volcanic, formed by the release of magma as part of the impact event, or a thick sheet of impact melt. Widespread areas of Mercury are covered by relatively flat, sparsely cratered plains materials. They fill depressions that range in size from regional troughs to crater floors. The smooth plains are similar to the maria of the Moon, an obvious difference being that the smooth plains have the same albedo as the intercrater plains. Smooth plains are most strikingly exposed in a broad annulus around the Caloris basin.
Geology of solar terrestrial planets | Mercury
Its mass is roughly half that of the planet Mercury. The smallest known planet orbiting a main-sequence star other than the Sun is Kepler-37b, with a mass (and radius) slightly higher than that of the Moon.
Planet | Mass
The following outline is provided as an overview of and topical guide to Mercury: Mercury – smallest and innermost planet in the Solar System. Its orbital period (about 88 Earth days) is less than any other planet in the Solar System. Seen from Earth, it appears to move around its orbit in about 116 days. It has no known natural satellites. It is named after the Roman deity Mercury, the messenger to the gods.
Outline of Mercury (planet) | Introduction
Non-crater surface features are given the following names:
Geology of Mercury | Terminology
List of geological features on Mercury is an itemization of mountains, valleys, craters and other landform features of the planet Mercury. Different types of features are named after different things: Mercurian ridges are called dorsa, and are named after astronomers who made detailed studies of the planet; valleys are called valles, and are named after ancient abandoned cities, towns, and settlements; crater chains are called catenae and are named after radio telescope facilities; plains are called planitiae, and most are named after mythological names associated with Mercury; escarpments are called rupes and are named after the ships of famous explorers; long, narrow depressions are called fossae and are named after works of architecture; bright spots are called faculae and are named after the word snake in various languages.
List of geological features on Mercury | Introduction
It is about long and belongs to the global system of scarps, which covers the entire surface of Mercury. These features are thought to have resulted from the global contraction of the planet as its interior cooled. The scarp is the youngest tectonic feature observed in this region, because it cuts all other units including smooth plains.
Rembrandt (crater) | Geology
The Lunar Reconnaissance Orbiter discovered that similar small thrust faults exist on the Moon.
Mercury (planet) | Compressional features
These created smooth intercrater plains similar to the maria found on the Moon. 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 ended when the planet's mantle had contracted enough to prevent further lava from breaking through to the surface. This probably occurred at some point during its first 700 or 800 million years of history. Since then, the main surface processes have been intermittent impacts.
Geology of Mercury | Mercury's geological history
There are two geologically distinct plains units on Mercury: The floor of the Caloris Basin is also filled by a geologically distinct flat plain, broken up by ridges and fractures in a roughly polygonal pattern. It is not clear whether they are volcanic lavas induced by the impact, or a large sheet of impact melt.
Geology of Mercury | Plains
See also list of craters on Mercury, list of albedo features on Mercury, and list of quadrangles on Mercury Longitude is west longitude.
List of geological features on Mercury | Introduction
There are two geologically distinct plains regions on Mercury. Gently rolling, hilly plains in the regions between craters are Mercury's oldest visible surfaces, predating the heavily cratered terrain. These inter-crater plains appear to have obliterated many earlier craters, and show a general paucity of smaller craters below about 30 km in diameter. Smooth plains are widespread flat areas that fill depressions of various sizes and bear a strong resemblance to the lunar maria. Notably, they fill a wide ring surrounding the Caloris Basin. Unlike lunar maria, the smooth plains of Mercury have the same albedo as the older inter-crater plains.
Mercury (planet) | Plains
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 may result in uneven surface weathering by the solar wind, knocking more surface particles up into the southern exosphere and transporting them for deposit in the north.
Geology of Mercury | Introduction
These are made by ejected debris, which tend to be brighter while they remain relatively fresh because of a lesser amount of space weathering than the surrounding older terrain.
Geology of Mercury | Impact basins and craters
Asteroids, comets, and meteoroids are all debris remaining from the nebula in which the Solar System formed 4.6 billion years ago.
Geology of solar terrestrial planets | Small Solar System bodies
Like the Earth, Moon and Mars, Mercury's geologic history is divided up into eras. From oldest to youngest, these are: the pre-Tolstojan, Tolstojan, Calorian, Mansurian, and Kuiperian. These ages are based on relative dating only. After the formation of Mercury along with the rest of the Solar System 4.6 billion years ago, heavy bombardment by asteroids and comets ensued. The last intense bombardment phase, the Late Heavy Bombardment came to an end about 3.8 billion years ago. Some regions or massifs, a prominent one being the one that formed the Caloris Basin, were filled by magma eruptions from within the planet.
Geology of Mercury | Mercury's geological history
Like the Moon and Venus, Mercury exhibits phases as seen from Earth. It is "new" at inferior conjunction and "full" at superior conjunction. The planet is rendered invisible from Earth on both of these occasions because of its being obscured by the Sun, except its new phase during a transit.
Mercury (planet) | Observation
51 Eridani b is a young Jupiter-like planet and was photographed, in near-infrared light, on December 21, 2014. The study, led by Bruce Macintosh, a professor of physics at Stanford University and confirmed by Christian Marois found that methane and water were abundant in the atmosphere of the planet and its mass was only slightly larger than Jupiter's. It is the smallest exoplanet directly imaged to date.
51 Eridani | Planetary system
There are eight planets in the Solar System, which are in increasing distance from the Sun: Jupiter is the largest, at 318 Earth masses, whereas Mercury is the smallest, at 0.055 Earth masses. The planets of the Solar System can be divided into categories based on their composition:
Planet | Solar System
At this time, it may appear as a bright star-like object, but is often far more difficult to observe than Venus. The planet telescopically displays the complete range of phases, similar to Venus and the Moon, as it moves in its inner orbit relative to Earth, which recurs over its synodic period of approximately 116 days. Mercury rotates in a way that is unique in the Solar System. It is tidally locked with the Sun in a 3:2 spin–orbit resonance, meaning that relative to the fixed stars, it rotates on its axis exactly three times for every two revolutions it makes around the Sun.
Mercury (planet) | Introduction
Mercurian craters have the morphological elements of lunar craters—the smaller craters are bowl-shaped, and with increasing size, they develop scalloped rims, central peaks, and terraces on the inner walls. The ejecta sheets have a hilly, lineated texture and swarms of secondary impact craters. Fresh craters of all sizes have dark or bright halos and well-developed ray systems. Although mercurian and lunar craters are superficially similar, they show subtle differences, especially in deposit extent. The continuous ejecta and fields of secondary craters on Mercury are far less extensive (by a factor of about 0.65) for a given rim diameter than those of comparable lunar craters.
Geology of solar terrestrial planets | Mercury
Mercury has a moment of inertia of 0.346, which is evidence for a core. Conservation of energy calculations as well as magnetic field measurements can also constrain composition, and surface geology of the planets can characterize differentiation of the body since its accretion. Mercury, Venus, and Mars’ cores are about 75%, 50%, and 40% of their radius respectively.
Planetary core | Cores of the Rocky Planets
Earth's crust is continually recycled by subduction at the boundaries of tectonic plates, and has an average age of about 100 million years, while Venus' surface is estimated to be about 500 million years old. Venusian craters range from to in diameter. There are no craters smaller than 3 km, because of the effects of the dense atmosphere on incoming objects. Objects with less than a certain kinetic energy are slowed down so much by the atmosphere that they do not create an impact crater.
Geology of solar terrestrial planets | Venus
Craters on Mercury range in diameter from small bowl-shaped craters to multi-ringed impact basins 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, with a diameter of 1550 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.
Geology of Mercury | Impact basins and craters
At least 15 ancient basins have been identified on Mercury. Tolstoj is a true multi-ring basin, displaying at least two, and possibly as many as four, concentric rings. It has a well-preserved ejecta blanket extending outward as much as from its rim. The basin interior is flooded with plains that clearly postdate the ejecta deposits. Beethoven has only one, subdued massif-like rim in diameter, but displays an impressive, well lineated ejecta blanket that extends as far as . As at Tolstoj, Beethoven ejecta is asymmetric. The Caloris basin is defined by a ring of mountains in diameter. Individual massifs are typically to long; the inner edge of the unit is marked by basin-facing scarps.
Geology of solar terrestrial planets | Mercury
This is a list of the lists of small Solar System bodies and dwarf planets.
Lists of small Solar System bodies | Introduction
Despite a lack of unequivocally volcanic characteristics, the localisation and rounded, lobate shape of these plains strongly support volcanic origins. All the smooth plains of Mercury 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 is 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.
Mercury (planet) | Plains
Scientists could not quantify the age of the volcanic complex system, but reported that it could be of the order of a billion years.
Mercury (planet) | Volcanology
Compared to many other planetary systems, the Solar System stands out in lacking planets interior to the orbit of Mercury. The known Solar System also lacks super-Earths (Planet Nine could be a super-Earth beyond the known Solar System). Uncommonly, it has only small rocky planets and large gas giants; elsewhere planets of intermediate size are typical—both rocky and gas—so there is no "gap" as seen between the size of Earth and of Neptune (with a radius 3.8 times as large). Also, these super-Earths have closer orbits than Mercury. This led to the hypothesis that all planetary systems start with many close-in planets, and that typically a sequence of their collisions causes consolidation of mass into few larger planets, but in case of the Solar System the collisions caused their destruction and ejection.
Solar System | Comparison with extrasolar systems
The data provided by "MESSENGER" has revealed a geologically complex planet.
Inter-crater plains on Mercury | Introduction
Its surface area is approximately the same as the land area of India or Argentina. In July 2018, NASA released a comparison of physical features found on Ceres with similar ones present on Earth. Ceres is the smallest object likely to be in hydrostatic equilibrium, being 600 km smaller and less than half the mass of Saturn's moon Rhea, the next smallest likely (but unproven) object. Modeling has suggested Ceres could have a small metallic core from partial differentiation of its rocky fraction, but the data is consistent with a mantle of hydrated silicates and no core.
Ceres (dwarf planet) | Geology
Ghost craters on the planet Mercury have tectonic features such as graben and wrinkle ridges. These features were formed by extensional and contractional forces originating in tectonic processes such as uplift and global contraction. The combination of graben and wrinkle ridges inside ghost craters found on Mercury has not been observed on any of the other terrestrial planets.
Ghost craters on Mercury | Introduction
The four smaller inner planets, Mercury, Venus, Earth and Mars, are terrestrial planets, being primarily composed of rock and metal. The four outer planets are giant planets, being substantially more massive than the terrestrials. The two largest planets, Jupiter and Saturn, are gas giants, being composed mainly of hydrogen and helium; the two outermost planets, Uranus and Neptune, are ice giants, being composed mostly of substances with relatively high melting points compared with hydrogen and helium, called volatiles, such as water, ammonia and methane. All eight planets have almost circular orbits that lie within a nearly flat disc called the ecliptic.
Solar System | Introduction
History of Mercury –
Outline of Mercury (planet) | History of Mercury
This difference results from the 2.5 times higher gravitational field on Mercury compared with the Moon. As on the Moon, impact craters on Mercury are progressively degraded by subsequent impacts. The freshest craters have ray systems and a crisp morphology. With further degradation, the craters lose their crisp morphology and rays and features on the continuous ejecta become more blurred until only the raised rim near the crater remains recognizable. Because craters become progressively degraded with time, the degree of degradation gives a rough indication of the crater's relative age. On the assumption that craters of similar size and morphology are roughly the same age, it is possible to place constraints on the ages of other underlying or overlying units and thus to globally map the relative age of craters.
Geology of solar terrestrial planets | Mercury
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 also has a similar-sized ejecta blanket and a 625 km diameter rim. As on the Moon, fresh craters on Mercury show prominent bright ray systems.
Geology of Mercury | Impact basins and craters
Lineated terrain extends for about out from the foot of a weak discontinuous scarp on the outer edge of the Caloris mountains; this terrain is similar to the "sculpture" surrounding the Imbrium basin on the Moon. Hummocky material forms a broad annulus about from the Caloris mountains. It consists of low, closely spaced to scattered hills about 0.3 to across and from tens of meters to a few hundred meters high. The outer boundary of this unit is gradational with the (younger) smooth plains that occur in the same region. A hilly and furrowed terrain is found antipodal to the Caloris basin, probably created by antipodal convergence of intense seismic waves generated by the Caloris impact.
Geology of solar terrestrial planets | Mercury
OGLE-2005-BLG-390L has one known planet, which was discovered using the technique of gravitational microlensing. Indications are that the planet is about five times Earth mass, orbiting at about 2.6 astronomical units from the parent star. The discovery was announced on January 25, 2006. OGLE-2005-BLG-390Lb was once considered one of the smallest known extrasolar planets around a main sequence star, possibly rocky, with a mass around 5.5 times that of the Earth. The orbital radius (assuming a circular orbit) of the planet is 2.6 AU, however the orbital elements are unknown. Based on its low mass and estimated temperature of around 50 K, the planet is thought to consist mainly of ices, like Pluto or Uranus, rather than being a Jupiter-like gas giant.
OGLE-2005-BLG-390L | Planetary system
Based on surface geology and albedo the sequence of creation of Mercury has been recorded and compared with that of the formation epochs of the Moon which show some similarities. The mapped region of Mercury shows intercrater plains, basins, smooth plains, craters and tectonic features. The earliest formation recorded is that of multi-ring basins (less than diameter) during the Pre-Tolstojan epoch; the morphologic features indicate domination of a single ring formation. The intercrater plains lie between and amidst large craters. Lobate scarps, seen extensively on planet Mercury, are in the form of undulating to arcuate scarps; wrinkle ridges are observed in the smooth plains materials.
Pre-Tolstojan | Geology
The geology of solar terrestrial planets mainly deals with the geological aspects of the four terrestrial planets of the Solar System – Mercury, Venus, Earth, and Mars – and one terrestrial dwarf planet: Ceres. Earth is the only terrestrial planet known to have an active hydrosphere. Terrestrial planets are substantially different from the giant planets, which might not have solid surfaces and are composed mostly of some combination of hydrogen, helium, and water existing in various physical states. Terrestrial planets have a compact, rocky surfaces, and Venus, Earth, and Mars each also have an atmosphere. Their size, radius, and density are all similar.
Geology of solar terrestrial planets | Introduction
The following craters on Mercury possess ray systems.
List of craters with ray systems | <a href="Mercury%20%28planet%29">Mercury</a>
Overall, about 15 impact basins have been identified on the imaged part of Mercury. A notable basin is the 400 km wide, multi-ring Tolstoj Basin that has an ejecta blanket extending up to 500 km from its rim and a floor that has been filled by smooth plains materials. Beethoven Basin has a similar-sized ejecta blanket and a 625 km diameter rim. Like the Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including Solar wind and micrometeorite impacts.
Mercury (planet) | Impact basins and craters
Two dark features had circular shapes and are presumably craters; one of them was observed to have a bright central region, whereas another was identified as the "Piazzi" feature. More recent visible-light Hubble Space Telescope images of a full rotation taken in 2003 and 2004 showed 11 recognizable surface features, the natures of which are currently unknown. One of these features corresponds to the "Piazzi" feature observed earlier.
Geology of solar terrestrial planets | Ceres
Craters on Mercury range in diameter from small bowl-shaped cavities to multi-ringed impact basins 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 in that the area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity. According to IAU rules, each new crater must be named after an artist that was famous for more than fifty years, and dead for more than three years, before the date the crater is named. The largest known crater is , with a diameter of 1,550 km.
Mercury (planet) | Impact basins and craters
It is possible that a planet in this system may have been scattered and ended up being accreted by the star, which may account for the large surface metallicity.
HD 12661 | Properties
The smaller planets retain only silicates, and are terrestrial planets like Earth or Mars, though multiple-"M" super-Earths have been discovered. The interior structure of rocky planets is mass-dependent: for example, plate tectonics may require a minimum mass to generate sufficient temperatures and pressures for it to occur.
Planetary mass | Planetary mass and planet formation
If a planet has a radius and/or mass between that of Earth and Neptune, then there is a question about whether the planet is rocky like Earth, a mixture of volatiles and gas like Neptune, a small planet with a hydrogen/helium envelope (mini-Jupiter), or of some other composition. Some of the Kepler transiting planets with radii in the range of 1–4 Earth radii have had their masses measured by radial-velocity or transit-timing methods. The calculated densities show that up to 1.5 Earth radii, these planets are rocky and that density increases with increasing radius due to gravitational compression. However, between 1.5 and 4 Earth radii the density decreases with increasing radius.
Exoplanetology | Super-Earths, mini-Neptunes, and gas dwarfs
With a minimum mass of around 4.5 Earths, it is a small Super-Earth.
Gliese 676 | Planetary system
Scientists are gathering telemetry to determine if such is the case.
Geology of Mercury | Introduction
Mercury has an observed magnetic field, which is believed to be generated within its metallic core. Mercury's core occupies 85% of the planet's radius, making it the largest core relative to the size of the planet in the Solar System; this indicates that much of Mercury's surface may have been lost early in the Solar System's history. Mercury has a solid silicate crust and mantle overlying a solid iron sulfide outer core layer, followed by a deeper liquid core layer, and then a possible solid inner core making a third layer.
Planetary core | Mercury
If the effect of gravitational compression were to be factored out from both planets, the materials of which Mercury is made would be denser than those of Earth, with an uncompressed density of 5.3 g/cm versus Earth's 4.4 g/cm. Mercury's density can be used to infer details of its inner structure. Although Earth's high density results appreciably from gravitational compression, particularly at the core, Mercury is much smaller and its inner regions are not as compressed. Therefore, for it to have such a high density, its core must be large and rich in iron.
Mercury (planet) | Internal structure
In fact, unfortunately, even though Mariner 10 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.
Geology of Mercury | Difficulties in exploration
Mercury and Venus are visible only in twilight hours because their orbits are interior to that of Earth. Venus is the third-brightest object in the sky and the most prominent planet. Mercury is more difficult to see due to its proximity to the Sun. Lengthy twilight and an extremely low angle at maximum elongations make optical filters necessary to see Mercury from extreme polar locations. Mars is at its brightest when it is in opposition, which occurs approximately every twenty-five months. Jupiter and Saturn are the largest of the five planets, but are farther from the Sun, and therefore receive less sunlight.
Classical planet | Naked-eye planets
The planet's mass has been estimated to be 8.65 times that of Jupiter, while its diameter, at , is 0.951 times Jupiter's. Its small size, despite the bloating of the planet's atmosphere, is caused by the strong gravity of the planet. This indicates its mean density is twice that of Earth and its surface gravity approximately 24 times that on Earth, almost equal to the Sun. The orbit is very eccentric, ranging from 4.90 million to 15.36 million miles from the star. In addition to heat from its primary star, tidal heating is thought to have played a significant role in this planet's evolution.
HAT-P-2b | Orbit and mass
Any reconstruction of mercurian geologic history must include the inference that at an early time the planet was differentiated into a core and crust. Mercury has a weak magnetic field coupled with high density. Both facts can most easily be accounted for by the presence of an iron core, possibly liquid, roughly 4,200 km in diameter, overlain by a silicate crust a few hundred kilometers thick. The postulated volcanic origin of a substantial fraction of the Mercurian plains also implies a thick silicate crust, and thereby supports the existence of a large iron core. Early, rather than late, differentiation of Mercury is attested to by the compressional scarps that are so clearly seen in the Discovery quadrangle.
Discovery quadrangle | Geologic history
Mercury and Venus).
Solar System | Inner planets
No images provide a vertical 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 wide range in sun-elevation angles, and the complete transection of the quadrangle by the gap in coverage greatly hamper geologic mapping. Only in about 15 percent of the quadrangle, near the southeast corner, do data permit separation of units with the confidence possible in other quadrangles on Mercury.
Victoria quadrangle | "Mariner 10" images
Venus is a planet with striking geology. Of all the other planets in the Solar System, it is the one nearest to Earth and most like it in terms of mass, but has no magnetic field or recognizable plate tectonic system. Much of the ground surface is exposed volcanic bedrock, some with thin and patchy layers of soil covering, in marked contrast with Earth, the Moon, and Mars. Some impact craters are present, but Venus is similar to Earth in that there are fewer craters than on the other rocky planets that are largely covered by them. This is due in part to the thickness of the Venusian atmosphere disrupting small impactors before they strike the ground, but the paucity of large craters may be due to volcanic re-surfacing, possibly of a catastrophic nature.
Geology of Venus | Introduction
This planet was typical as it was discovered spectroscopically using the radial velocity method.
HD 167042 b | Introduction
As on the Moon and Mars, sequences of craters and basins of differing relative ages provide the best means of establishing stratigraphic order on Mercury. Overlap relations among many large mercurian craters and basins are clearer than those on the Moon. Therefore, as this map shows, we can build up many local stratigraphic columns involving both crater or basin materials and nearby plains materials. Over all of Mercury, the crispness of crater rims and the morphology of their walls, central peaks, ejecta deposits, and secondary-crater fields have undergone systematic changes with time. The youngest craters or basins in a local stratigraphic sequence have the sharpest, crispest appearance.
List of craters on Mercury | Terminology
The small planet radius gap (also called the Fulton gap, photoevaporation valley, or Sub-Neptune Desert) is an observed scarcity of planets with radii between 1.5 and 2 times Earth's radius, likely due to photoevaporation-driven mass loss. A bimodality in the Kepler exoplanet population was first observed in 2013, and was noted as possibly confirming an emerging hypothesis that photoevaporation could drive atmospheric mass loss on close-in, low-mass planets. This would lead to a population of bare, rocky cores with smaller radii at small separations from their parent stars, and planets with thick hydrogen- and helium-dominated envelopes with larger radii at larger separations.
Small planet radius gap | Introduction
The single known planet orbiting this star was identified as a candidate based on photometry from the first four months of data from the Kepler spacecraft. Confirmation was obtained in 2012 after extensive follow-up observations and analysis of the Kepler light curves. The calculated density of the planet is approximately 6.4 g cm, similar to earth's 5.5 g cm, which suggests a rocky composition. With an equilibrium temperature of 2025 Kelvin, the top few-hundred kilometers of the planet is probably molten.
HD 179070 | Planetary system
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" team members have suggested that such pits formed by the collapse of subsurface magma chambers. If this suggestion is correct, the pits are evidence of volcanic processes at work on Mercury. Pit craters are rimless, often irregularly shaped, and steep-sided, and they display no associated ejecta or lava flows but are typically distinctive in color. For example, the pits of Praxiteles 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.
Geology of Mercury | Pit-floor craters
This made close observation of both sides of the planet impossible, and resulted in the mapping of less than 45% of the planet's surface. The spacecraft made three close approaches to Mercury, the closest of which took it to within of the surface. At the first close approach, instruments detected a magnetic field, to the great surprise of planetary geologists—Mercury's rotation was expected to be much too slow to generate a significant dynamo effect. The second close approach was primarily used for imaging, but at the third approach, extensive magnetic data were obtained. The data revealed that the planet's magnetic field is much like Earth's, which deflects the solar wind around the planet.
Mercury (planet) | "Mariner 10"
Depending on composition the two planets may be around the same size, or HD 154345 b may be larger. This planet may also harbor a system of moons and rings.
HD 154345 b | Characteristics
Uranus and Neptune, which are smaller, have rocky cores surrounded by mantles of water, ammonia, methane and other ices. The fluid action within these planets' cores creates a geodynamo that generates a magnetic field.
Planet | Internal differentiation
However, there are also fewer of the large craters, and those appear relatively young; they are rarely filled with lava, showing that they happened after volcanic activity in the area, and radar shows that they are rough and have not had time to be eroded down. Much of Venus' surface appears to have been shaped by volcanic activity. Overall, Venus has several times as many volcanoes as Earth, and it possesses some 167 giant volcanoes that are over across. The only volcanic complex of this size on Earth is the Big Island of Hawaii. However, this is not because Venus is more volcanically active than Earth, but because its crust is older.
Geology of solar terrestrial planets | Venus
However, the surface characteristics are consistent with a completely random distribution, implying that the surface of the entire planet is roughly the same age, or at least that very large areas are not very different in age from the average.
Geology of Venus | Impact craters and age estimates of the surface
This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the Universe's history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations.
Kepler-444 | Characteristics
Major craters exhibiting these features include Beckett, Gibran and Lermontov, among others. It was suggested that these pits with associated brighter and redder deposits may be pyroclastic deposits caused by explosive volcanism.
Geology of Mercury | Pit-floor craters
As seen from the Sun, in a frame of reference that rotates with the orbital motion, it appears to rotate only once every two Mercurian years. An observer on Mercury would therefore see only one day every two Mercurian years.
Mercury (planet) | Introduction
Brown estimates it is likely a dwarf planet based on its presumed size, calculated from its absolute magnitude (H) and assumed albedo.
(144897) 2004 UX10 | Introduction
On June 13 2002, a 2.1 M planet HD 73526 b was announced orbiting HD 73526 in an orbit just a little smaller than that of Venus' orbit around the Sun. This planet receives insolation 3.65 times that of Earth or 1.89 times that of Venus. This was a single planet system until 2006 when a 2.3 M second planet HD 73526 c was discovered. This planet forms a 2:1 orbital resonance with planet b. Although these are minimum masses as the inclinations of these planets are unknown, orbital stability analysis indicated that orbital inclinations of both planets are likely to be near 90°, making the minimum masses very close to the true masses of the planets.
HD 73526 | Planetary system
Wrinkle ridges are tectonic feature where sections of the crust are uplifted. Wrinkle ridges are associated with compressional stresses. On Mercury, the planet's interior is cooling and contracting. This contraction creates planet-wide compression. Wrinkle ridges on Mercury are thought to come from material loaded on top of the volcanic plains, in addition to the cooling. When plains have volcanic material deposited on top, the lithosphere can flex and create more compressional stresses.
Ghost craters on Mercury | Wrinkle ridges
of the planet’s life; the oldest major rock units in this quadrangle are probably at least 2 to 3 b.y. old. The geologic history of Mercury has been summarized by Guest and O’Donnell (1977), Davies and others, and Strom.
Shakespeare quadrangle | Geologic history
(See List of smallest exoplanets.)
Geophysical definition of 'planet' | Applicability to exoplanets
At the time of discovery of the planet HD 49674 b in 2002, it was the least massive planet known, very close to the boundary between sub-Jupiter mass and Neptune-mass at 0.1 M. This planet orbits very close to the star.
HD 49674 | Planetary system
It is argued that life requires terrestrial planets like Earth and as gas giants lack such a surface, that complex life cannot arise there. A planet that is too small cannot hold much atmosphere, making surface temperature low and variable and oceans impossible. A small planet will also tend to have a rough surface, with large mountains and deep canyons. The core will cool faster, and plate tectonics may be brief or entirely absent. A planet that is too large will retain too dense an atmosphere like Venus. Although Venus is similar in size and mass to Earth, its surface atmospheric pressure is 92 times that of Earth, and surface temperature of 735 K (462 °C; 863 °F).
Rare Earth hypothesis | A terrestrial planet of the right size
The sizes are listed in units of Earth radii (). All planets listed are smaller than Earth and being up to 0.7 Earth radii.
List of smallest exoplanets | List
HD 168443 b is a planet with a minimum mass seven times as that of Jupiter. Given the high mass, this planet is likely to be a gas giant, or possibly a small brown dwarf depending on the orbital inclination. It orbits closer to its star than Mercury does to the Sun, and its surface temperature is likely to be very high. It was discovered in 1999 using radial velocity measurements taken at the W. M. Keck Observatory in Hawaii.
HD 168443 b | Introduction
This occurs about every seven years on average. Mercury's axial tilt is almost zero, with the best measured value as low as 0.027 degrees. This is significantly smaller than that of Jupiter, which has the second smallest axial tilt of all planets at 3.1 degrees. This means that to an observer at Mercury's poles, the center of the Sun never rises more than 2.1 arcminutes above the horizon.
Mercury (planet) | Orbit, rotation, and longitude
The Solar System, showing the Sun and the planets in the order of their position from the Sun: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. (Pluto has since been reclassified as a dwarf planet by the International Astronomical Union, but it was considered a planet at the time the message was transmitted.) The Earth is the third planet from the Sun; its graphic is shifted up to identify it as the planet from which the signal was sent. Additionally, the human figure is shown just above the Earth graphic. In addition to showing position, the graphic provides a general, not-to-scale size reference of each planet and the Sun.
Arecibo message | Planets
Its orbital eccentricity is unknown. In comparison, Mercury orbits the Sun every 87.97 days at a distance of 0.387 AU. Kepler-11f has an orbital inclination of 89.4°; it can be seen almost edge-on with respect to Earth. Its surface equilibrium temperature is 544 K, over twice the surface equilibrium temperature of Earth and about two-thirds the surface temperature of Venus. Kepler-11f's low density, characteristic of the outer planets of the system, suggests that a hydrogen–helium atmosphere is present on these planets, classifying it as "gas dwarf" due to its small size and mass. The gaseous content of the planet is calculated at a few percent of its total mass, but the envelope accounts for 70-80% of the planet's total volume.
Kepler-11f | Characteristics
The tectonic features on Mercury were not studied in precise detail until the "MESSENGER" spacecraft was sent to Mercury; by 2009 the "MESSENGER" spacecraft had mapped 98% of the planet's surface. By 2013, Messenger mapped 100% of the planet's surface. Mercury Dual Imaging System cameras and Mercury Laser Altimeter equipment on the messenger spacecraft allowed for researchers to obtain high-resolution images of the planet's surface for analyzing Mercury's tectonics.
Ghost craters on Mercury | Discovery
This is a directory of lists of geological features on planets excepting Earth, moons and asteroids ordered by increasing distance from the Sun.
Lists of geological features of the Solar System | Introduction
By comparison, the Antarctic ice sheet on Earth has a mass of about 4 kg, and Mars's south polar cap contains about 10 kg of water. The origin of the ice on Mercury is not yet known, but the two most likely sources are from outgassing of water from the planet's interior or deposition by impacts of comets.
Mercury (planet) | Surface conditions and exosphere
No certain connection has been made between these features and the topographic features viewed on Mercury by the Mariner 10 spacecraft. Mariner 10, however, imaged less than half of Mercury's surface.
List of albedo features on Mercury | Introduction
It may have a relatively high eccentricity of 0.4. This object has at least 13 times the mass of the Earth.
HD 96700 | Planetary system
Structural features are sparse or unresolved in this part of Mercury. The Kuiper quadrangle apparently has none of the scarps that occur elsewhere on the planet that have been interpreted as high-angle reverse faults. The most prominent structures are the rings associated with some large craters or basins, faults that transect crater floors, and lobate scarps and ridges in the plains materials. Most of the faults and scarps that transect crater floors clearly delineate crater-filling materials standing at different levels, and in at least two craters (19° S., 31°; 16° N., 30°), the traces of the faults on the crater walls indicate that the faults have normal displacements.
Kuiper quadrangle | Structure