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84-721: The Cherang'any Hills were formed due to Faulting. They form the western flank of the Gregory Rift Valley (East African Rift Valley) that stretches from Djibouti in the North to Mozambique in the South. They are located on a forested escarpment with sheer cliff walls surrounding them on three sides. Rocks found in Cherangani Hills are majorly Gneisses rich in Biotite and Muscovite. A Gneiss sample from Chepsiro, one of

168-406: A 3:2 ratio. This relationship is called spin–orbit resonance , and sidereal here means "relative to the stars". Consequently, one solar day (sunrise to sunrise) on Mercury lasts for around 176 Earth days: twice the planet's sidereal year. This means that one side of Mercury will remain in sunlight for one Mercurian year of 88 Earth days; while during the next orbit, that side will be in darkness all

252-424: A conduit. Scientists could not quantify the age of the volcanic complex system but reported that it could be on the order of a billion years. The surface temperature of Mercury ranges from 100 to 700 K (−173 to 427 °C; −280 to 800 °F). It never rises above 180 K at the poles, due to the absence of an atmosphere and a steep temperature gradient between the equator and the poles. At perihelion ,

336-460: A fault displaces the ground surface so that one side is higher than the other, a fault scarp is created. This can occur in dip-slip faults , or when a strike-slip fault brings a piece of high ground adjacent to an area of lower ground. Earth is not the only planet where escarpments occur. They are believed to occur on other planets when the crust contracts , as a result of cooling. On other Solar System bodies such as Mercury , Mars , and

420-474: A general paucity of smaller craters below about 30 km (19 mi) in diameter. Smooth plains are widespread flat areas that fill depressions of various sizes and bear a strong resemblance to lunar maria. Unlike lunar maria, the smooth plains of Mercury have the same albedo as the older inter-crater plains. Despite a lack of unequivocally volcanic characteristics, the localization and rounded, lobate shape of these plains strongly support volcanic origins. All

504-566: A layer of regolith that inhibits sublimation . By comparison, the Antarctic ice sheet on Earth has a mass of about 4 × 10  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 and deposition by impacts of comets. Mercury is too small and hot for its gravity to retain any significant atmosphere over long periods of time; it does have

588-528: A layered, chemically heterogeneous crust with large-scale variations in chemical composition observed on the surface. The crust is low in iron but high in sulfur, resulting from the stronger early chemically reducing conditions than is found on other terrestrial planets. The surface is dominated by iron-poor pyroxene and olivine , as represented by enstatite and forsterite , respectively, along with sodium-rich plagioclase and minerals of mixed magnesium, calcium, and iron-sulfide. The less reflective regions of

672-487: A possibly separate subsequent episode called the Late Heavy Bombardment that ended 3.8 billion years ago. Mercury received impacts over its entire surface during this period of intense crater formation, facilitated by the lack of any atmosphere to slow impactors down. During this time Mercury was volcanically active; basins were filled by magma , producing smooth plains similar to the maria found on

756-551: A prolonged interval. A "rimless depression" inside the southwest rim of the Caloris Basin consists of at least nine overlapping volcanic vents, each individually up to 8 km (5.0 mi) in diameter. It is thus a " compound volcano ". The vent floors are at least 1 km (0.62 mi) below their brinks and they bear a closer resemblance to volcanic craters sculpted by explosive eruptions or modified by collapse into void spaces created by magma withdrawal back down into

840-462: A revolution would have caused a libration of 23.65° in longitude. For the same reason, there are two points on Mercury's equator, 180 degrees apart in longitude , at either of which, around perihelion in alternate Mercurian years (once a Mercurian day), the Sun passes overhead, then reverses its apparent motion and passes overhead again, then reverses a second time and passes overhead a third time, taking

924-429: A series of smaller "corpuscules") might exist in an orbit even closer to the Sun than that of Mercury, to account for this perturbation. Other explanations considered included a slight oblateness of the Sun. The success of the search for Neptune based on its perturbations of the orbit of Uranus led astronomers to place faith in this possible explanation, and the hypothetical planet was named Vulcan , but no such planet

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1008-465: A solid, metallic outer core layer, a deeper liquid core layer, and a solid inner core. The composition of the iron-rich core remains uncertain, but it likely contains nickel, silicon and perhaps sulfur and carbon, plus trace amounts of other elements. The planet'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 . If

1092-409: A tenuous surface-bounded exosphere at a surface pressure of less than approximately 0.5 nPa (0.005 picobars). It includes hydrogen , helium , oxygen , sodium , calcium , potassium , magnesium , silicon , and hydroxide , among others. This exosphere is not stable—atoms are continuously lost and replenished from a variety of sources. Hydrogen atoms and helium atoms probably come from

1176-409: A total of about 16 Earth-days for this entire process. In the other alternate Mercurian years, the same thing happens at the other of these two points. The amplitude of the retrograde motion is small, so the overall effect is that, for two or three weeks, the Sun is almost stationary overhead, and is at its most brilliant because Mercury is at perihelion, its closest to the Sun. This prolonged exposure to

1260-524: Is 17%. Research published in 2007 suggests that Mercury has a molten core. The mantle-crust layer is in total 420 km (260 mi) thick. Projections differ as to the size of the crust specifically; data from the Mariner 10 and MESSENGER probes suggests a thickness of 35 km (22 mi), whereas an Airy isostacy model suggests a thickness of 26 ± 11 km (16.2 ± 6.8 mi). One distinctive feature of Mercury's surface

1344-424: Is a rocky body like Earth. It is the smallest planet in the Solar System, with an equatorial radius of 2,439.7 kilometres (1,516.0 mi). 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 appears to have a solid silicate crust and mantle overlying

1428-605: Is heavily cratered , as a result of countless impact events that have accumulated over billions of years. Its largest crater, Caloris Planitia , has a diameter of 1,550 km (960 mi), which is about one-third the diameter of the planet (4,880 km or 3,030 mi). Similarly to the Earth 's Moon , Mercury's surface displays an expansive rupes system generated from thrust faults and bright ray systems formed by impact event remnants . Mercury's sidereal year (88.0 Earth days) and sidereal day (58.65 Earth days) are in

1512-560: Is highly homogeneous, which suggests that Mercury had a magma ocean early in its history, like the Moon. According to current models , Mercury may have a solid silicate crust and mantle overlying a solid outer core, a deeper liquid core layer, and a solid inner core. There are many competing hypotheses about Mercury's origins and development, some of which incorporate collision with planetesimals and rock vaporization. Historically, humans knew Mercury by different names depending on whether it

1596-461: Is in May or November. 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

1680-436: Is stabilized by the variance of the tidal force along Mercury's eccentric orbit, acting on a permanent dipole component of Mercury's mass distribution. In a circular orbit there is no such variance, so the only resonance stabilized in such an orbit is at 1:1 (e.g., Earth–Moon), when the tidal force, stretching a body along the "center-body" line, exerts a torque that aligns the body's axis of least inertia (the "longest" axis, and

1764-427: Is that Mercury originally had a metal–silicate ratio similar to common chondrite meteorites, thought to be typical of the Solar System's rocky matter, and a mass approximately 2.25 times its current mass. Early in the Solar System's history, Mercury may have been struck by a planetesimal of approximately 1 ⁄ 6 Mercury's mass and several thousand kilometers across. The impact would have stripped away much of

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1848-419: Is the presence of numerous narrow ridges, extending up to several hundred kilometers in length. It is thought that these were formed as Mercury's core and mantle cooled and contracted at a time when the crust had already solidified. Mercury's core has a higher iron content than that of any other planet in the Solar System, and several theories have been proposed to explain this. The most widely accepted theory

1932-400: The Mariner 10 and MESSENGER space probes have indicated that the strength and shape of the magnetic field are stable. It is likely that this magnetic field is generated by a dynamo effect, in a manner similar to the magnetic field of Earth. This dynamo effect would result from the circulation of the planet's iron-rich liquid core. Particularly strong tidal heating effects caused by

2016-716: The Cherangani Hills Forest . The De Brazza's monkey has been sighted here. The monkeys are confined to small areas in the Cherang'any Hills that offer them little protection. This Kenya location article is a stub . You can help Misplaced Pages by expanding it . Escarpment An escarpment is a steep slope or long cliff that forms as a result of faulting or erosion and separates two relatively level areas having different elevations . The terms scarp and scarp face are often used interchangeably with escarpment . Some sources differentiate

2100-577: The Moon , the Latin term rupes is used for an escarpment. When sedimentary beds are tilted and exposed to the surface, erosion and weathering may occur. Escarpments erode gradually and over geological time . The mélange tendencies of escarpments results in varying contacts between a multitude of rock types. These different rock types weather at different speeds, according to Goldich dissolution series so different stages of deformation can often be seen in

2184-486: The VLA in the early 1990s revealed that there are patches of high radar reflection near the poles. Although ice was not the only possible cause of these reflective regions, astronomers thought it to be the most likely explanation. The presence of water ice was confirmed using MESSENGER images of craters at the north pole. The icy crater regions are estimated to contain about 10 –10  kg of ice, and may be covered by

2268-459: The antipode of the Caloris Basin is a large region of unusual, hilly terrain known as the "Weird Terrain". One hypothesis for its origin is that shock waves generated during the Caloris impact traveled around Mercury, converging at the basin's antipode (180 degrees away). The resulting high stresses fractured the surface. Alternatively, it has been suggested that this terrain formed as a result of

2352-472: 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. The radius of Mercury's core is estimated to be 2,020 ± 30 km (1,255 ± 19 mi), based on interior models constrained to be consistent with a moment of inertia factor of 0.346 ± 0.014 . Hence, Mercury's core occupies about 57% of its volume; for Earth this proportion

2436-488: The solar wind . A third hypothesis proposes that the solar nebula caused drag on the particles from which Mercury was accreting , which meant that lighter particles were lost from the accreting material and not gathered by Mercury. Each hypothesis predicts a different surface composition, and two space missions have been tasked with making observations of this composition. The first MESSENGER , which ended in 2015, found higher-than-expected potassium and sulfur levels on

2520-403: The 1980s–1990s, and are thought to result primarily from the vaporization of surface rock struck by micrometeorite impacts including presently from Comet Encke . In 2008, magnesium was discovered by MESSENGER . Studies indicate that, at times, sodium emissions are localized at points that correspond to the planet's magnetic poles. This would indicate an interaction between the magnetosphere and

2604-428: The Caloris Basin was so powerful that it caused lava eruptions and left a concentric mountainous ring ~2 km (1.2 mi) tall surrounding the impact crater . 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 were volcanic lava flows induced by the impact or a large sheet of impact melt. At

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2688-582: The Greek Hermes, because it moves across the sky faster than any other planet, though some associated the planet with Apollo instead, as detailed by Pliny the Elder . The astronomical symbol for Mercury is a stylized version of Hermes' caduceus ; a Christian cross was added in the 16th century: [REDACTED] . Mercury is one of four terrestrial planets in the Solar System , which means it

2772-676: The Major Tributaries of River Nzoia. Visible are forested ridges and stark, rocky gorges. The hills form the source of Moiben River, one of the two tributaries of the Nzoia River , the other being Mount Elgon . The Cherang'any Hills are monitored by the United Nations Environmental Programme as one of the five most important water catchment areas in Kenya. As of the last report, monitoring

2856-442: The Moon, the surface of Mercury has likely incurred the effects of space weathering processes, including solar wind and micrometeorite impacts. 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

2940-524: The Moon. One of the most unusual craters is Apollodorus , or "the Spider", which hosts a series of radiating troughs extending outwards from its impact site. 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

3024-400: The Sun at its brightest makes these two points the hottest places on Mercury. Maximum temperature occurs when the Sun is at an angle of about 25 degrees past noon due to diurnal temperature lag , at 0.4 Mercury days and 0.8 Mercury years past sunrise. Conversely, there are two other points on the equator, 90 degrees of longitude apart from the first ones, where the Sun passes overhead only when

3108-442: The Sun's apparent motion ceases; closer to perihelion, Mercury's angular orbital velocity then exceeds the angular rotational velocity. Thus, to a hypothetical observer on Mercury, the Sun appears to move in a retrograde direction. Four Earth days after perihelion, the Sun's normal apparent motion resumes. A similar effect would have occurred if Mercury had been in synchronous rotation: the alternating gain and loss of rotation over

3192-448: The Sun) on Mercury last exactly two Mercury years, or about 176 Earth days. Mercury's orbit is inclined by 7 degrees to the plane of Earth's orbit (the ecliptic ), the largest of all eight known solar planets. As a result, transits of Mercury across the face of the Sun can only occur when the planet is crossing the plane of the ecliptic at the time it lies between Earth and the Sun, which

3276-551: The Sun, collide with Venus, be ejected from the Solar System, or even disrupt the rest of the inner Solar System. In 1859, the French mathematician and astronomer Urbain Le Verrier reported that the slow precession of Mercury's orbit around the Sun could not be completely explained by Newtonian mechanics and perturbations by the known planets. He suggested, among possible explanations, that another planet (or perhaps instead

3360-470: The Sun. This varying distance to the Sun leads to Mercury's surface being flexed by tidal bulges raised by the Sun that are about 17 times stronger than the Moon's on Earth. Combined with a 3:2 spin–orbit resonance of the planet's rotation around its axis, it also results in complex variations of the surface temperature. The resonance makes a single solar day (the length between two meridian transits of

3444-463: The area blanketed by their ejecta is much smaller, a consequence of Mercury's stronger surface gravity. According to International Astronomical Union rules, each new crater must be named after an artist who 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 Caloris Planitia , or Caloris Basin, with a diameter of 1,550 km (960 mi). The impact that created

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3528-410: The axis of the aforementioned dipole) to always point at the center. However, with noticeable eccentricity, like that of Mercury's orbit, the tidal force has a maximum at perihelion and therefore stabilizes resonances, like 3:2, ensuring that the planet points its axis of least inertia roughly at the Sun when passing through perihelion. The original reason astronomers thought it was synchronously locked

3612-421: The base of the plateau . Scarps are generally formed by one of two processes: either by differential erosion of sedimentary rocks , or by movement of the Earth's crust at a geologic fault . The first process is the more common type: the escarpment is a transition from one series of sedimentary rocks to another series of a different age and composition. Escarpments are also frequently formed by faults. When

3696-491: The change in forestation between 2000 and 2003, the Cherang'any Hills were the least affected of the forests monitored, with 174.3 hectares deforested, this loss is occurring within Marakwet District and West Pokot District . Since this forest cover is indigenous , the report recommends that the area be closely watched to prevent further destruction. The thirteen forest reserves there are collectively known as

3780-433: The convergence of ejecta at this basin's antipode. Overall, 46 impact basins have been identified. A notable basin is the 400 km (250 mi)-wide, multi-ring Tolstoj Basin that has an ejecta blanket extending up to 500 km (310 mi) 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 (388 mi)-diameter rim. Like

3864-438: The craters. Above the planet's surface is an extremely tenuous exosphere and a faint magnetic field that is strong enough to deflect solar winds . Mercury has no natural satellite . As of the early 2020s, many broad details of Mercury's geological history are still under investigation or pending data from space probes. Like other planets in the Solar System, Mercury was formed approximately 4.5 billion years ago. Its mantle

3948-503: The crust are high in carbon, most likely in the form of graphite. Names for features on Mercury come from a variety of sources and are set according to the IAU planetary nomenclature system. 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

4032-473: The data is needed. 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. It is more heterogeneous than the surface of Mars or the Moon, both of which contain significant stretches of similar geology, such as maria and plateaus. Albedo features are areas of markedly different reflectivity, which include impact craters,

4116-438: The early 20th century, Albert Einstein 's general theory of relativity provided the explanation for the observed precession, by formalizing gravitation as being mediated by the curvature of spacetime. The effect is small: just 42.980 ± 0.001 arcseconds per century (or 0.43 arcsecond per year, or 0.1035 arcsecond per orbital period) for Mercury; it therefore requires a little over 12.5 million orbits, or 3 million years, for

4200-408: 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

4284-404: The effects of the eccentricity, showing Mercury's orbit overlaid with a circular orbit having the same semi-major axis . Mercury's higher velocity when it is near perihelion is clear from the greater distance it covers in each 5-day interval. In the diagram, the varying distance of Mercury to the Sun is represented by the size of the planet, which is inversely proportional to Mercury's distance from

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4368-427: The equatorial subsolar point is located at latitude 0°W or 180°W, and it climbs to a temperature of about 700 K . During aphelion , this occurs at 90° or 270°W and reaches only 550 K . On the dark side of the planet, temperatures average 110 K . The intensity of sunlight on Mercury's surface ranges between 4.59 and 10.61 times the solar constant (1,370 W·m ). Although daylight temperatures at

4452-420: The features has suggested a total shrinkage of Mercury's radius in the range of ~1–7 km (0.62–4.35 mi). Most activity along the major thrust systems probably ended about 3.6–3.7 billion years ago. Small-scale thrust fault scarps have been found, tens of meters in height and with lengths in the range of a few kilometers, that appear to be less than 50 million years old, indicating that compression of

4536-516: The horizon. By comparison, the angular size of the Sun as seen from Mercury ranges from 1 + 1 ⁄ 4 to 2 degrees across. At certain points on Mercury's surface, an observer would be able to see the Sun peek up a little more than two-thirds of the way over the horizon, then reverse and set before rising again, all within the same Mercurian day . This is because approximately four Earth days before perihelion, Mercury's angular orbital velocity equals its angular rotational velocity so that

4620-429: The interior and consequent surface geological activity continue to the present. There is evidence for pyroclastic flows on Mercury from low-profile shield volcanoes . Fifty-one pyroclastic deposits have been identified, where 90% of them are found within impact craters. A study of the degradation state of the impact craters that host pyroclastic deposits suggests that pyroclastic activity occurred on Mercury over

4704-456: The layers where the escarpments have been exposed to the elements. Mercury (planet) Mercury is the first planet from the Sun and the smallest in the Solar System . In English, it is named after the ancient Roman god Mercurius ( Mercury ), god of commerce and communication, and the messenger of the gods. Mercury is classified as a terrestrial planet , with roughly the same surface gravity as Mars . The surface of Mercury

4788-510: The orbital eccentricity of Mercury varies chaotically from nearly zero (circular) to more than 0.45 over millions of years due to perturbations from the other planets. This was thought to explain Mercury's 3:2 spin-orbit resonance (rather than the more usual 1:1), because this state is more likely to arise during a period of high eccentricity. However, accurate modeling based on a realistic model of tidal response has demonstrated that Mercury

4872-678: The original crust and mantle, leaving the core behind as a relatively major component. A similar process, known as the giant impact hypothesis , has been proposed to explain the formation of Earth's Moon. Alternatively, Mercury may have formed from the solar nebula before the Sun's energy output had stabilized. It would initially have had twice its present mass, but as the protosun contracted, temperatures near Mercury could have been between 2,500 and 3,500 K and possibly even as high as 10,000 K. Much of Mercury's surface rock could have been vaporized at such temperatures, forming an atmosphere of "rock vapor" that could have been carried away by

4956-407: The permanently shadowed polar craters. The detection of high amounts of water-related ions like O , OH , and H 3 O was a surprise. Because of the quantities of these ions that were detected in Mercury's space environment, scientists surmise that these molecules were blasted from the surface or exosphere by the solar wind. Sodium, potassium, and calcium were discovered in the atmosphere during

5040-528: The planet is at aphelion in alternate years, when the apparent motion of the Sun in Mercury's sky is relatively rapid. These points, which are the ones on the equator where the apparent retrograde motion of the Sun happens when it is crossing the horizon as described in the preceding paragraph, receive much less solar heat than the first ones described above. Mercury attains an inferior conjunction (nearest approach to Earth) every 116 Earth days on average, but this interval can range from 105 days to 129 days due to

5124-571: The planet's eccentric orbit. Mercury can come as near as 82,200,000 km (0.549 astronomical units; 51.1 million miles) to Earth, and that is slowly declining: The next approach to within 82,100,000 km (51 million mi) is in 2679, and to within 82,000,000 km (51 million mi) in 4487, but it will not be closer to Earth than 80,000,000 km (50 million mi) until 28,622. Its period of retrograde motion as seen from Earth can vary from 8 to 15 days on either side of an inferior conjunction. This large range arises from

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5208-458: The planet's high orbital eccentricity would serve to keep part of the core in the liquid state necessary for this dynamo effect. Mercury's magnetic field is strong enough to deflect the solar wind around the planet, creating a magnetosphere. The planet's magnetosphere, though small enough to fit within Earth, is strong enough to trap solar wind plasma . This contributes to the space weathering of

5292-441: The planet's high orbital eccentricity. Essentially, because Mercury is closest to the Sun, when taking an average over time, Mercury is most often the closest planet to the Earth, and—in that measure—it is the closest planet to each of the other planets in the Solar System. The longitude convention for Mercury puts the zero of longitude at one of the two hottest points on the surface, as described above. However, when this area

5376-442: The planet's surface. According to NASA, Mercury is not a suitable planet for Earth-like life. It has a surface boundary exosphere instead of a layered atmosphere, extreme temperatures, and high solar radiation. It is unlikely that any living beings can withstand those conditions. Some parts of the subsurface of Mercury may have been habitable , and perhaps life forms , albeit likely primitive microorganisms , may have existed on

5460-504: The planet's surface. Observations taken by the Mariner 10 spacecraft detected this low energy plasma in the magnetosphere of the planet's nightside. Bursts of energetic particles in the planet's magnetotail indicate a dynamic quality to the planet's magnetosphere. During its second flyby of the planet on October 6, 2008, MESSENGER discovered that Mercury's magnetic field can be extremely "leaky". The spacecraft encountered magnetic "tornadoes"—twisted bundles of magnetic fields connecting

5544-482: The planet. Despite its small size and slow 59-day-long rotation, Mercury has a significant, and apparently global, magnetic field . According to measurements taken by Mariner 10 , it is about 1.1% the strength of Earth's . The magnetic-field strength at Mercury's equator is about 300 nT . Like that of Earth, Mercury's magnetic field is dipolar and nearly aligned with the planet's spin axis (10° dipolar tilt, compared to 11° for Earth). Measurements from both

5628-439: The planetary magnetic field to interplanetary space—that were up to 800 km wide or a third of the radius of the planet. These twisted magnetic flux tubes, technically known as flux transfer events , form open windows in the planet's magnetic shield through which the solar wind may enter and directly impact Mercury's surface via magnetic reconnection . This also occurs in Earth's magnetic field. The MESSENGER observations showed

5712-458: The reconnection rate was ten times higher at Mercury, but its proximity to the Sun only accounts for about a third of the reconnection rate observed by MESSENGER . Mercury has the most eccentric orbit of all the planets in the Solar System; its eccentricity is 0.21 with its distance from the Sun ranging from 46,000,000 to 70,000,000 km (29,000,000 to 43,000,000 mi). It takes 87.969 Earth days to complete an orbit. The diagram illustrates

5796-450: The resulting ejecta, and ray systems . Larger albedo features correspond to higher reflectivity plains. Mercury has " wrinkle-ridges " (dorsa), Moon-like highlands , mountains (montes), plains (planitiae), escarpments (rupes), and valleys ( valles ). The planet's mantle is chemically heterogeneous, suggesting the planet went through a magma ocean phase early in its history. Crystallization of minerals and convective overturn resulted in

5880-445: The same face directed towards the Sun, in the same way that the same side of the Moon always faces Earth. Radar observations in 1965 proved that the planet has a 3:2 spin-orbit resonance, rotating three times for every two revolutions around the Sun. The eccentricity of Mercury's orbit makes this resonance stable—at perihelion, when the solar tide is strongest, the Sun is nearly stationary in Mercury's sky. The 3:2 resonant tidal locking

5964-563: The smaller peaks of Cherangani was found to be containing Iron Ore. White Quartzite rocks are found in Lelan in West Pokot. Other minerals that have been recorded before by Geologists in Cherangani Hills include Red Garnets near Talau in West Pokot and Beryl in Sebit. Chromite has also been found by Geologists in the colonial era. The Cheranganyi Hills are a source to River Moiben and Chepkaitit,

6048-756: 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. An unusual feature of Mercury's surface is the numerous compression folds, or rupes , that crisscross the plains. These exist on the Moon, but are much more prominent on Mercury. 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 1,000 km (620 mi) and heights of 3 km (1.9 mi). These compressional features can be seen on top of other features, such as craters and smooth plains, indicating they are more recent. Mapping of

6132-452: The solar wind, diffusing into Mercury's magnetosphere before later escaping back into space. The radioactive decay of elements within Mercury's crust is another source of helium, as well as sodium and potassium. Water vapor is present, released by a combination of processes such as comets striking its surface, sputtering creating water out of hydrogen from the solar wind and oxygen from rock, and sublimation from reservoirs of water ice in

6216-514: 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 was heavily bombarded by comets and asteroids during and shortly following its formation 4.6 billion years ago, as well as during

6300-445: The surface of Mercury are generally extremely high, observations strongly suggest that ice (frozen water) exists on Mercury. The floors of deep craters at the poles are never exposed to direct sunlight, and temperatures there remain below 102 K, far lower than the global average. This creates a cold trap where ice can accumulate. Water ice strongly reflects radar , and observations by the 70-meter Goldstone Solar System Radar and

6384-406: The surface, suggesting that the giant impact hypothesis and vaporization of the crust and mantle did not occur because said potassium and sulfur would have been driven off by the extreme heat of these events. BepiColombo , which will arrive at Mercury in 2025, will make observations to test these hypotheses. The findings so far would seem to favor the third hypothesis; however, further analysis of

6468-456: The time until the next sunrise after another 88 Earth days. Combined with its high orbital eccentricity , the planet's surface has widely varying sunlight intensity and temperature, with the equatorial regions ranging from −170 °C (−270 °F) at night to 420 °C (790 °F) during sunlight. Due to the very small axial tilt , the planet's poles are permanently shadowed . This strongly suggests that water ice could be present in

6552-439: The two terms, with escarpment referring to the margin between two landforms , and scarp referring to a cliff or a steep slope. In this usage an escarpment is a ridge which has a gentle slope on one side and a steep scarp on the other side. More loosely, the term scarp also describes a zone between a coastal lowland and a continental plateau which shows a marked, abrupt change in elevation caused by coastal erosion at

6636-480: The westerly direction on Mercury. The two hottest places on the equator are therefore at longitudes 0° W and 180° W, and the coolest points on the equator are at longitudes 90° W and 270° W. However, the MESSENGER project uses an east-positive convention. For many years it was thought that Mercury was synchronously tidally locked with the Sun, rotating once for each orbit and always keeping

6720-487: Was an evening star or a morning star. By about 350 BC, the ancient Greeks had realized the two stars were one. They knew the planet as Στίλβων Stilbōn , meaning "twinkling", and Ἑρμής Hermēs , for its fleeting motion, a name that is retained in modern Greek ( Ερμής Ermis ). The Romans named the planet after the swift-footed Roman messenger god, Mercury (Latin Mercurius ), whom they equated with

6804-464: Was captured into the 3:2 spin-orbit state at a very early stage of its history, within 20 (more likely, 10) million years after its formation. Numerical simulations show that a future secular orbital resonant interaction with the perihelion of Jupiter may cause the eccentricity of Mercury's orbit to increase to the point where there is a 1% chance that the orbit will be destabilized in the next five billion years. If this happens, Mercury may fall into

6888-520: Was ever found. The observed perihelion precession of Mercury is 5,600 arcseconds (1.5556°) per century relative to Earth, or 574.10 ± 0.65 arcseconds per century relative to the inertial ICRF . Newtonian mechanics, taking into account all the effects from the other planets and including 0.0254 arcseconds per century due to the oblateness of the Sun, predicts a precession of 5,557 arcseconds (1.5436°) per century relative to Earth, or 531.63 ± 0.69 arcseconds per century relative to ICRF. In

6972-472: Was first visited, by Mariner 10 , this zero meridian was in darkness, so it was impossible to select a feature on the surface to define the exact position of the meridian. Therefore, a small crater further west was chosen, called Hun Kal , which provides the exact reference point for measuring longitude. The center of Hun Kal defines the 20° west meridian. A 1970 International Astronomical Union resolution suggests that longitudes be measured positively in

7056-460: Was that, whenever Mercury was best placed for observation, it was always nearly at the same point in its 3:2 resonance, hence showing the same face. This is because, coincidentally, Mercury's rotation period is almost exactly half of its synodic period with respect to Earth. Due to Mercury's 3:2 spin-orbit resonance, a solar day lasts about 176 Earth days. A sidereal day (the period of rotation) lasts about 58.7 Earth days. Simulations indicate that

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