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64-471: Occator / ɒ ˈ k eɪ t ər / is an impact crater located on Ceres , the largest object in the main asteroid belt that lies between the orbits of Mars and Jupiter , that contains "Spot 5", the brightest of the bright spots observed by the Dawn spacecraft . It was known as "Region A" in ground-based images taken by the W. M. Keck Observatory on Mauna Kea . The crater was named after Occator ,

128-433: A paraboloid (bowl-shaped) crater in which the centre has been pushed down, a significant volume of material has been ejected, and a topographically elevated crater rim has been pushed up. When this cavity has reached its maximum size, it is called the transient cavity. The depth of the transient cavity is typically a quarter to a third of its diameter. Ejecta thrown out of the crater do not include material excavated from

192-450: A central depression rather than a central peak, with its original central peak having collapsed into 9–10 km wide depression, ~1 km deeper than the crater floor. Data indicates that magnesium sulfide (MgS) deposits were in place after the central peak's uplift and collapse. The central depression also contains a 2 km wide dome, which is encompassed by several dense fractures along its flanks. The northern and southern edges of

256-468: A certain altitude (retardation point), and start to accelerate again due to Earth's gravity until the body reaches its terminal velocity of 0.09 to 0.16 km/s. The larger the meteoroid (i.e. asteroids and comets) the more of its initial cosmic velocity it preserves. While an object of 9,000 kg maintains about 6% of its original velocity, one of 900,000 kg already preserves about 70%. Extremely large bodies (about 100,000 tonnes) are not slowed by

320-561: A deep internal reservoir to the surface at Occator crater was first modeled in 2019. A small dome in the center of the crater is 3 km across and about 340 meters height. It is named Cerealia Tholus and is covered by bright salt deposits named Cerealia Facula . The group of thinner salt deposits to the east are named Vinalia Faculae [sic]. In July 2018, NASA released a comparison of physical features, including Occator, found on Ceres with similar ones present on Earth. Between 2015 and 2017 five different attempts were made to discern

384-455: A hole in the surface without filling in nearby craters. This may explain the 'sponge-like' appearance of that moon. It is convenient to divide the impact process conceptually into three distinct stages: (1) initial contact and compression, (2) excavation, (3) modification and collapse. In practice, there is overlap between the three processes with, for example, the excavation of the crater continuing in some regions while modification and collapse

448-452: A large impact. The subsequent excavation of the crater occurs more slowly, and during this stage the flow of material is largely subsonic. During excavation, the crater grows as the accelerated target material moves away from the point of impact. The target's motion is initially downwards and outwards, but it becomes outwards and upwards. The flow initially produces an approximately hemispherical cavity that continues to grow, eventually producing

512-558: A regular sequence with increasing size: small complex craters with a central topographic peak are called central peak craters, for example Tycho ; intermediate-sized craters, in which the central peak is replaced by a ring of peaks, are called peak-ring craters , for example Schrödinger ; and the largest craters contain multiple concentric topographic rings, and are called multi-ringed basins , for example Orientale . On icy (as opposed to rocky) bodies, other morphological forms appear that may have central pits rather than central peaks, and at

576-409: A result, the impactor is compressed, its density rises, and the pressure within it increases dramatically. Peak pressures in large impacts exceed 1 T Pa to reach values more usually found deep in the interiors of planets, or generated artificially in nuclear explosions . In physical terms, a shock wave originates from the point of contact. As this shock wave expands, it decelerates and compresses

640-620: A sample of articles of confirmed and well-documented impact sites. See the Earth Impact Database , a website concerned with 190 (as of July 2019 ) scientifically confirmed impact craters on Earth. There are approximately twelve more impact craters/basins larger than 300 km on the Moon, five on Mercury, and four on Mars. Large basins, some unnamed but mostly smaller than 300 km, can also be found on Saturn's moons Dione, Rhea and Iapetus. Magnesium sulfide MgS

704-441: A significant crater volume may also be formed by the permanent compaction of the pore space . Such compaction craters may be important on many asteroids, comets and small moons. In large impacts, as well as material displaced and ejected to form the crater, significant volumes of target material may be melted and vaporized together with the original impactor. Some of this impact melt rock may be ejected, but most of it remains within

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768-406: A small angle, and high-temperature highly shocked material is expelled from the convergence zone with velocities that may be several times larger than the impact velocity. In most circumstances, the transient cavity is not stable and collapses under gravity. In small craters, less than about 4 km diameter on Earth, there is some limited collapse of the crater rim coupled with debris sliding down

832-431: A smaller object. In contrast to volcanic craters , which result from explosion or internal collapse, impact craters typically have raised rims and floors that are lower in elevation than the surrounding terrain. Impact craters are typically circular, though they can be elliptical in shape or even irregular due to events such as landslides. Impact craters range in size from microscopic craters seen on lunar rocks returned by

896-402: Is already underway in others. In the absence of atmosphere , the impact process begins when the impactor first touches the target surface. This contact accelerates the target and decelerates the impactor. Because the impactor is moving so rapidly, the rear of the object moves a significant distance during the short-but-finite time taken for the deceleration to propagate across the impactor. As

960-512: Is ejected from close to the center of impact, and the slowest material is ejected close to the rim at low velocities to form an overturned coherent flap of ejecta immediately outside the rim. As ejecta escapes from the growing crater, it forms an expanding curtain in the shape of an inverted cone. The trajectory of individual particles within the curtain is thought to be largely ballistic. Small volumes of un-melted and relatively un-shocked material may be spalled at very high relative velocities from

1024-459: Is estimated that the value of materials mined from impact structures is five billion dollars/year just for North America. The eventual usefulness of impact craters depends on several factors, especially the nature of the materials that were impacted and when the materials were affected. In some cases, the deposits were already in place and the impact brought them to the surface. These are called "progenetic economic deposits." Others were created during

1088-518: Is formed by the reaction of sulfur or hydrogen sulfide with magnesium . It crystallizes in the rock salt structure as its most stable phase, its zinc blende and wurtzite structures can be prepared by molecular beam epitaxy . The chemical properties of MgS resemble those of related ionic sulfides such as those of sodium, barium, or calcium. It reacts with oxygen to form the corresponding sulfate, magnesium sulfate . MgS reacts with water to give hydrogen sulfide and magnesium hydroxide . In

1152-404: Is sufficient to melt the impactor, and in larger impacts to vaporize most of it and to melt large volumes of the target. As well as being heated, the target near the impact is accelerated by the shock wave, and it continues moving away from the impact behind the decaying shock wave. Contact, compression, decompression, and the passage of the shock wave all occur within a few tenths of a second for

1216-413: Is the brightest region of the dwarf planet Ceres . Occator is the central feature of its eponymous quadrungle. The Ac-9 shows heavily fractured crater floors and is consistently shallow compared to similar size non-fractured crater floors.     Impact crater An impact crater is a depression in the surface of a solid astronomical body formed by the hypervelocity impact of

1280-437: Is the largest goldfield in the world, which has supplied about 40% of all the gold ever mined in an impact structure (though the gold did not come from the bolide). The asteroid that struck the region was 9.7 km (6 mi) wide. The Sudbury Basin was caused by an impacting body over 9.7 km (6 mi) in diameter. This basin is famous for its deposits of nickel , copper , and platinum group elements . An impact

1344-814: The Apollo Program to simple bowl-shaped depressions and vast, complex, multi-ringed impact basins . Meteor Crater is a well-known example of a small impact crater on Earth. Impact craters are the dominant geographic features on many solid Solar System objects including the Moon , Mercury , Callisto , Ganymede , and most small moons and asteroids . On other planets and moons that experience more active surface geological processes, such as Earth , Venus , Europa , Io , Titan , and Triton , visible impact craters are less common because they become eroded , buried, or transformed by tectonic and volcanic processes over time. Where such processes have destroyed most of

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1408-462: The BOS steelmaking process, sulfur is the first element to be removed. Sulfur is removed from the impure blast furnace iron by the addition of several hundred kilograms of magnesium powder by a lance. Magnesium sulfide is formed, which then floats on the molten iron and is removed. MgS is a wide band-gap direct semiconductor of interest as a blue-green emitter , a property that has been known since

1472-497: The Nevada Test Site , notably Jangle U in 1951 and Teapot Ess in 1955. In 1960, Edward C. T. Chao and Shoemaker identified coesite (a form of silicon dioxide ) at Meteor Crater, proving the crater was formed from an impact generating extremely high temperatures and pressures. They followed this discovery with the identification of coesite within suevite at Nördlinger Ries , proving its impact origin. Armed with

1536-429: The speed of sound in those objects. Such hyper-velocity impacts produce physical effects such as melting and vaporization that do not occur in familiar sub-sonic collisions. On Earth, ignoring the slowing effects of travel through the atmosphere, the lowest impact velocity with an object from space is equal to the gravitational escape velocity of about 11 km/s. The fastest impacts occur at about 72 km/s in

1600-399: The stable interior regions of continents . Few undersea craters have been discovered because of the difficulty of surveying the sea floor, the rapid rate of change of the ocean bottom, and the subduction of the ocean floor into Earth's interior by processes of plate tectonics . Daniel M. Barringer, a mining engineer, was convinced already in 1903 that the crater he owned, Meteor Crater ,

1664-493: The "worst case" scenario in which an object in a retrograde near-parabolic orbit hits Earth. The median impact velocity on Earth is about 20 km/s. However, the slowing effects of travel through the atmosphere rapidly decelerate any potential impactor, especially in the lowest 12 kilometres where 90% of the Earth's atmospheric mass lies. Meteorites of up to 7,000 kg lose all their cosmic velocity due to atmospheric drag at

1728-531: The Dawn mission located a bright region on the Occator crater floor. The material in this region was determined to have a dominant composition of sodium (Na) carbonates, aluminium (Al) phyllosilicates, and ammonium chloride (NH 4 Cl). Occator crater’s central 1 km deep depression displays a pronounced luminous feature named Cerealia Facula. Like most 70-150 km wide Ceresian impact craters, Occator has

1792-484: The Occator impactor, the body was made of igneous rock and was approximately 5 km in diameter, with an estimated velocity range of 4.8 km/sec to 7.5 km/sec and a target surface lithology of icy-rock material. The simulation variables produced an 80 km impact crater with a central peak and a crater depth of 15 – 30 km. Discovered in March 6, 2015 during the early stages of mapping of Ceres's surface,

1856-580: The Roman god of the harrow and a helper to Ceres. The name Occator was officially approved by the IAU on 3 July 2015. On 9 December 2015, scientists reported that the bright spots on Ceres , including those in Occator, may be related to a type of salt, particularly a form of brine containing magnesium sulfate hexahydrite (MgSO 4 ·6H 2 O); the spots were also found to be associated with ammonia-rich clays . More recently, on 29 June 2016, scientists reported

1920-478: The actual impact. The great energy involved caused melting. Useful minerals formed as a result of this energy are classified as "syngenetic deposits." The third type, called "epigenetic deposits," is caused by the creation of a basin from the impact. Many of the minerals that our modern lives depend on are associated with impacts in the past. The Vredeford Dome in the center of the Witwatersrand Basin

1984-404: The age of Occator. The age dating models of the lobate flows and crater ejecta range from 200 million years to 78 million years and 100 million years to 6.09 million. The age ranges have different chronology models, image data at verifying resolution, and different methods to evaluate the data. The current data estimates an age of impact at ~20 to 24.5 million years; however, the estimates are of

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2048-469: The association of volcanic flows and other volcanic materials. Impact craters produce melted rocks as well, but usually in smaller volumes with different characteristics. The distinctive mark of an impact crater is the presence of rock that has undergone shock-metamorphic effects, such as shatter cones , melted rocks, and crystal deformations. The problem is that these materials tend to be deeply buried, at least for simple craters. They tend to be revealed in

2112-432: The atmosphere at all, and impact with their initial cosmic velocity if no prior disintegration occurs. Impacts at these high speeds produce shock waves in solid materials, and both impactor and the material impacted are rapidly compressed to high density. Following initial compression, the high-density, over-compressed region rapidly depressurizes, exploding violently, to set in train the sequence of events that produces

2176-449: The base of the crater wall that extends into the central depression. The crater floor comprises three central morphological units, which divide the crater into zones. The outermost unit or terrace zone along the crater wall forms a circumferential pattern. This unit contains hummocky and angular material with small to large, tilted fault blocks that vary in size up to ~10 km in diameter and up to 2 km in height. The interior zone of

2240-409: The bright spot to be mostly sodium carbonate ( Na 2 CO 3 ), implying that hydrothermal activity was probably involved in creating the bright spots. In August 2020, NASA confirmed that Ceres was a water-rich body with a deep reservoir of brine that percolated to the surface in various locations causing the "bright spots" , including those in Occator crater. The percolation of brine from

2304-441: The central dome and opens to the structure’s northwest. The local relief of the topography within the lobate deposits of the southern half of the interior zone constraints within ~100 m. The topography relief of the western half of the interior zone has a gentle increase of the slope ~500 m. The asymmetrical change in relief of the lobate deposits located in the southern half of the interior indicates two significant factors. First,

2368-451: The collapse and modification of the transient cavity is much more extensive, and the resulting structure is called a complex crater . The collapse of the transient cavity is driven by gravity, and involves both the uplift of the central region and the inward collapse of the rim. The central uplift is not the result of elastic rebound, which is a process in which a material with elastic strength attempts to return to its original geometry; rather

2432-468: The collapse is a process in which a material with little or no strength attempts to return to a state of gravitational equilibrium . Complex craters have uplifted centers, and they have typically broad flat shallow crater floors, and terraced walls . At the largest sizes, one or more exterior or interior rings may appear, and the structure may be labeled an impact basin rather than an impact crater. Complex-crater morphology on rocky planets appears to follow

2496-415: The convex profile of the crater are rimless with slopes of <10°, while the eastern and western edges of the crater’s depressions are dominated by irregular high standing massifs that formed an incomplete rim around the crater edge. The Occator crater floor is covered in linear impact fractures from the southwest to the central depression. These fractures cross over the northeast lobate flow deposits at

2560-424: The crater is divided into two different units that have two different morphological characteristics. The Northwestern Interior Zone is primarily hummocky material similar to the terrace zone material. This northwestern unit topography is formed of irregular mounds and uneven ridges and laterally blends into the hummocky faulted terrace unit along the crater wall, making this section very difficult to distinguish between

2624-451: The crater walls and drainage of impact melts into the deeper cavity. The resultant structure is called a simple crater, and it remains bowl-shaped and superficially similar to the transient crater. In simple craters, the original excavation cavity is overlain by a lens of collapse breccia , ejecta and melt rock, and a portion of the central crater floor may sometimes be flat. Above a certain threshold size, which varies with planetary gravity,

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2688-405: The craters on the Moon as logical impact sites that were formed not gradually, in eons , but explosively, in seconds." For his PhD degree at Princeton University (1960), under the guidance of Harry Hammond Hess , Shoemaker studied the impact dynamics of Meteor Crater. Shoemaker noted that Meteor Crater had the same form and structure as two explosion craters created from atomic bomb tests at

2752-407: The expanding vapor cloud may rise to many times the scale height of the atmosphere, effectively expanding into free space. Most material ejected from the crater is deposited within a few crater radii, but a small fraction may travel large distances at high velocity, and in large impacts it may exceed escape velocity and leave the impacted planet or moon entirely. The majority of the fastest material

2816-401: The full depth of the transient cavity; typically the depth of maximum excavation is only about a third of the total depth. As a result, about one third of the volume of the transient crater is formed by the ejection of material, and the remaining two thirds is formed by the displacement of material downwards, outwards and upwards, to form the elevated rim. For impacts into highly porous materials,

2880-448: The geologists John D. Boon and Claude C. Albritton Jr. revisited Bucher's studies and concluded that the craters that he studied were probably formed by impacts. Grove Karl Gilbert suggested in 1893 that the Moon's craters were formed by large asteroid impacts. Ralph Baldwin in 1949 wrote that the Moon's craters were mostly of impact origin. Around 1960, Gene Shoemaker revived the idea. According to David H. Levy , Shoemaker "saw

2944-599: The impact crater. Impact-crater formation is therefore more closely analogous to cratering by high explosives than by mechanical displacement. Indeed, the energy density of some material involved in the formation of impact craters is many times higher than that generated by high explosives. Since craters are caused by explosions , they are nearly always circular – only very low-angle impacts cause significantly elliptical craters. This describes impacts on solid surfaces. Impacts on porous surfaces, such as that of Hyperion , may produce internal compression without ejecta, punching

3008-432: The impactor made an oblique angle impact trending from the southeast to the northwest. Second, the target had variations in composition or topography that altered the impact. Near the central depression and slightly offset from the center is an ~ 3 km wide dome structure with an upper surface densely covered in cross pattern fractures. These fractures become less evident along the flanks and are believed not to extend into

3072-521: The impactor, and it accelerates and compresses the target. Stress levels within the shock wave far exceed the strength of solid materials; consequently, both the impactor and the target close to the impact site are irreversibly damaged. Many crystalline minerals can be transformed into higher-density phases by shock waves; for example, the common mineral quartz can be transformed into the higher-pressure forms coesite and stishovite . Many other shock-related changes take place within both impactor and target as

3136-764: The knowledge of shock-metamorphic features, Carlyle S. Beals and colleagues at the Dominion Astrophysical Observatory in Victoria, British Columbia , Canada and Wolf von Engelhardt of the University of Tübingen in Germany began a methodical search for impact craters. By 1970, they had tentatively identified more than 50. Although their work was controversial, the American Apollo Moon landings, which were in progress at

3200-649: The largest sizes may contain many concentric rings. Valhalla on Callisto is an example of this type. Long after an impact event, a crater may be further modified by erosion, mass wasting processes, viscous relaxation, or erased entirely. These effects are most prominent on geologically and meteorologically active bodies such as Earth, Titan, Triton, and Io. However, heavily modified craters may be found on more primordial bodies such as Callisto, where many ancient craters flatten into bright ghost craters, or palimpsests . Non-explosive volcanic craters can usually be distinguished from impact craters by their irregular shape and

3264-411: The original crater topography , the terms impact structure or astrobleme are more commonly used. In early literature, before the significance of impact cratering was widely recognised, the terms cryptoexplosion or cryptovolcanic structure were often used to describe what are now recognised as impact-related features on Earth. The cratering records of very old surfaces, such as Mercury, the Moon, and

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3328-711: The outer Solar System could be different from the inner Solar System. Although Earth's active surface processes quickly destroy the impact record, about 190 terrestrial impact craters have been identified. These range in diameter from a few tens of meters up to about 300 km (190 mi), and they range in age from recent times (e.g. the Sikhote-Alin craters in Russia whose creation was witnessed in 1947) to more than two billion years, though most are less than 500 million years old because geological processes tend to obliterate older craters. They are also selectively found in

3392-479: The planet than have been discovered so far. The cratering rate in the inner solar system fluctuates as a consequence of collisions in the asteroid belt that create a family of fragments that are often sent cascading into the inner solar system. Formed in a collision 80 million years ago, the Baptistina family of asteroids is thought to have caused a large spike in the impact rate. The rate of impact cratering in

3456-468: The sample areas with some uncertainty and variability due to arbitrary cratering and the use of different models to date the impact. Thermal evolution of a large melt chamber below Occator Crater constrained the age of the impact is closer to 18 million years, this is evident in the difference between impact geology and formation of the Cerealia Facula ( bright spot ). According to a simulation of

3520-419: The shock wave passes through, and some of these changes can be used as diagnostic tools to determine whether particular geological features were produced by impact cratering. As the shock wave decays, the shocked region decompresses towards more usual pressures and densities. The damage produced by the shock wave raises the temperature of the material. In all but the smallest impacts this increase in temperature

3584-464: The southern highlands of Mars, record a period of intense early bombardment in the inner Solar System around 3.9 billion years ago. The rate of crater production on Earth has since been considerably lower, but it is appreciable nonetheless. Earth experiences, on average, from one to three impacts large enough to produce a 20-kilometre-diameter (12 mi) crater every million years. This indicates that there should be far more relatively young craters on

3648-425: The surface of the target and from the rear of the impactor. Spalling provides a potential mechanism whereby material may be ejected into inter-planetary space largely undamaged, and whereby small volumes of the impactor may be preserved undamaged even in large impacts. Small volumes of high-speed material may also be generated early in the impact by jetting. This occurs when two surfaces converge rapidly and obliquely at

3712-410: The terrace and interior zones.  The material within these zones shows significant displacement from direct relation to the crater wall slumping and floor uplift during the impact event. The southern half of the crater interior zone is primarily a flat, low-lying topography of lobate deposits covering an estimated 1/3rd of the interior crater floor. Most of the southern u-shaped zone is formed around

3776-473: The time, provided supportive evidence by recognizing the rate of impact cratering on the Moon . Because the processes of erosion on the Moon are minimal, craters persist. Since the Earth could be expected to have roughly the same cratering rate as the Moon, it became clear that the Earth had suffered far more impacts than could be seen by counting evident craters. Impact cratering involves high velocity collisions between solid objects, typically much greater than

3840-411: The transient crater, initially forming a layer of impact melt coating the interior of the transient cavity. In contrast, the hot dense vaporized material expands rapidly out of the growing cavity, carrying some solid and molten material within it as it does so. As this hot vapor cloud expands, it rises and cools much like the archetypal mushroom cloud generated by large nuclear explosions. In large impacts,

3904-403: The uplifted center of a complex crater, however. Impacts produce distinctive shock-metamorphic effects that allow impact sites to be distinctively identified. Such shock-metamorphic effects can include: On Earth, impact craters have resulted in useful minerals. Some of the ores produced from impact related effects on Earth include ores of iron , uranium , gold , copper , and nickel . It

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3968-409: The walls of the depression (pit) structure. The bright material deposits extend to the inward-facing wall of the depression and transition to the dome structure’s exterior wall. This deposition pattern indicates the deposits formed within the contiguous geological unit and that the uplift and fracturing formed before deposition. The Ac-9 Occator quadrangle is located on an elevated equatorial region and

4032-684: Was involved in making the Carswell structure in Saskatchewan , Canada; it contains uranium deposits. Hydrocarbons are common around impact structures. Fifty percent of impact structures in North America in hydrocarbon-bearing sedimentary basins contain oil/gas fields. On Earth, the recognition of impact craters is a branch of geology, and is related to planetary geology in the study of other worlds. Out of many proposed craters, relatively few are confirmed. The following twenty are

4096-519: Was of cosmic origin. Most geologists at the time assumed it formed as the result of a volcanic steam eruption. In the 1920s, the American geologist Walter H. Bucher studied a number of sites now recognized as impact craters in the United States. He concluded they had been created by some great explosive event, but believed that this force was probably volcanic in origin. However, in 1936,

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