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Arachnoid (astrogeology)
In astrogeology, an arachnoid is a large geological structure resembling a spider web. They are of unknown origin, and have been found only on the surface of the planet Venus. They appear as concentric ovals surrounded by a complex network of fractures, and can span 200 kilometers. Over 90 arachnoids have been identified on Venus. Arachnoids could be related to volcanos, however it is also possible that different arachnoids are formed by different processes.This article contains text from the Astronomy Picture of the Daybr> As a work of the United States Federal Government, it is in the public domain. One possible explanation is that an upwelling of magma from the interior of the planet pushed up on the surface, causing cracks. An alternate theory concerning their origin is that they are a precursor to Corona (planetary geology), coronae formation. Much of what is known about arachnoids is the result of studies performed by C.B. Dawson and L.S. Crumpler. See also * Chaos ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astrogeology
Planetary geology, alternatively known as astrogeology or exogeology, is a planetary science discipline concerned with the geology of the celestial bodies such as the planets and their moons, asteroids, comets, and meteorites. Although the geo- prefix typically indicates topics of or relating to Earth, planetary geology is named as such for historical and convenience reasons; due to the types of investigations involved, it is closely linked with Earth-based geology. These investigations are centered around the composition, structure, processes, and history of a planet. Planetary geology includes such topics as determining the properties and processes of the internal structure of the terrestrial planets, and also looks at planetary volcanism and surface processes such as impact craters, fluvial and aeolian processes. The structures and compositions of the giant planets and their moons are also examined, as is the make-up of the minor bodies of the Solar System, such as asteroids ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Spider Web
A spider web, spiderweb, spider's web, or cobweb (from the archaic word '' coppe'', meaning "spider") is a structure created by a spider out of proteinaceous spider silk extruded from its spinnerets, generally meant to catch its prey. Spider webs have existed for at least 100 million years, as witnessed in a rare find of Early Cretaceous amber from Sussex, in southern England. Many spiders build webs specifically to trap and catch insects to eat. However, not all spiders catch their prey in webs, and some do not build webs at all. "Spider web" is typically used to refer to a web that is apparently still in use (i.e. clean), whereas "cobweb" refers to abandoned (i.e. dusty) webs. However, the word "cobweb" is also used by biologists to describe the tangled three-dimensional web of some spiders of the family Theridiidae. While this large family is known as the cobweb spiders, they actually have a huge range of web architectures; other names for this spider family include tang ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Planet Venus
Venus is the second planet from the Sun. It is sometimes called Earth's "sister" or "twin" planet as it is almost as large and has a similar composition. As an interior planet to Earth, Venus (like Mercury) appears in Earth's sky never far from the Sun, either as morning star or evening star. Aside from the Sun and Moon, Venus is the brightest natural object in Earth's sky, capable of casting visible shadows on Earth at dark conditions and being visible to the naked eye in broad daylight. Venus is the second largest terrestrial object of the Solar System. It has a surface gravity slightly lower than on Earth and has a very weak induced magnetosphere. The atmosphere of Venus, mainly consists of carbon dioxide, and is the densest and hottest of the four terrestrial planets at the surface. With an atmospheric pressure at the planet's surface of about 92 times the sea level pressure of Earth and a mean temperature of , the carbon dioxide gas at Venus's surface is in the s ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Concentric
In geometry, two or more objects are said to be concentric, coaxal, or coaxial when they share the same center or axis. Circles, regular polygons and regular polyhedra, and spheres may be concentric to one another (sharing the same center point), as may cylinders (sharing the same central axis). Geometric properties In the Euclidean plane, two circles that are concentric necessarily have different radii from each other.. However, circles in three-dimensional space may be concentric, and have the same radius as each other, but nevertheless be different circles. For example, two different meridians of a terrestrial globe are concentric with each other and with the globe of the earth (approximated as a sphere). More generally, every two great circles on a sphere are concentric with each other and with the sphere. By Euler's theorem in geometry on the distance between the circumcenter and incenter of a triangle, two concentric circles (with that distance being zero) are ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fracture
Fracture is the separation of an object or material into two or more pieces under the action of stress. The fracture of a solid usually occurs due to the development of certain displacement discontinuity surfaces within the solid. If a displacement develops perpendicular to the surface, it is called a normal tensile crack or simply a crack; if a displacement develops tangentially, it is called a shear crack, slip band or dislocation. Brittle fractures occur with no apparent deformation before fracture. Ductile fractures occur after visible deformation. Fracture strength, or breaking strength, is the stress when a specimen fails or fractures. The detailed understanding of how a fracture occurs and develops in materials is the object of fracture mechanics. Strength Fracture strength, also known as breaking strength, is the stress at which a specimen fails via fracture. This is usually determined for a given specimen by a tensile test, which charts the stress–strain ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcano
A volcano is a rupture in the Crust (geology), crust of a Planet#Planetary-mass objects, planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and volcanic gas, gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where list of tectonic plates, tectonic plates are divergent boundary, diverging or convergent boundary, converging, and most are found underwater. For example, a mid-ocean ridge, such as the Mid-Atlantic Ridge, has volcanoes caused by divergent tectonic plates whereas the Pacific Ring of Fire has volcanoes caused by convergent tectonic plates. Volcanoes can also form where there is stretching and thinning of the crust's plates, such as in the East African Rift and the Wells Gray-Clearwater volcanic field and Rio Grande rift in North America. Volcanism away from plate boundaries has been postulated to arise from upwelling diapirs from the core–mantle boundary, deep in the Earth. This results in hotspot ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Astronomy Picture Of The Day
Astronomy Picture of the Day (APOD) is a website provided by NASA and Michigan Technological University (MTU). According to the website, "Each day a different image or photograph of our universe is featured, along with a brief explanation written by a professional astronomer." The photograph does not necessarily correspond to a celestial event on the exact day that it is displayed, and images are sometimes repeated. However, the pictures and descriptions often relate to current events in astronomy and space exploration. The text has several hyperlinks to more pictures and websites for more information. The images are either visible spectrum photographs, images taken at non-visible wavelengths and displayed in false color, video footage, animations, artist's conceptions, or micrographs that relate to space or cosmology. Past images are stored in the APOD Archive, with the first image appearing on June 16, 1995. This initiative has received support from NASA, the National Science ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Corona (planetary Geology)
In planetary geology, a corona (plural: coronae ) is an oval-shaped feature. Coronae appear on both the planet Venus and Uranus's moon Miranda and may be formed by upwellings of warm material below the surface. Coronae on Venus The geodynamic surface of Venus is dominated by patterns of basaltic volcanism, and by compressional and extensional tectonic deformation, such as the highly deformed tesserae terrain and the concentrically-fractured coronae. On Venus, coronae are large (typically several hundred kilometres across), crown-like, volcanic features. Coronae were first identified in 1983, when the radar imaging equipment aboard the Venera 15 and Venera 16 spacecraft produced higher-resolution images of some features previously thought to be impact craters. It is believed that coronae are formed when plumes of rising hot material in the mantle push the crust upwards into a dome shape, which then collapses in the centre as the molten magma cools and leaks out at the sides, ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Chaos Terrain
In astrogeology, chaos terrain, or chaotic terrain, is a planetary surface area where features such as ridges, cracks, and plains appear jumbled and enmeshed with one another. Chaos terrain is a notable feature of the planets Mars and Mercury, Jupiter's moon Europa, and the dwarf planet Pluto. In scientific nomenclature, "chaos" is used as a component of proper nouns (e.g., " Aureum Chaos" on Mars). On Mars Wikichaosmap.jpg, Tography map of Oxia Palus region of Mars showing the location of a number of chaos regions Mapbeer.jpg, Map showing location of Arsinoes Chaos (far left), Iani Chaos, Aureum Chaos, Margaritifer Chaos, and other nearby features Image:Margaritifer Sinus Map.JPG, Map of Margaritifer Sinus quadrangle with major features labeled. Aureum Chaos is near the top of the map. Image:Canyons and Mesas of Aureum Chaos in Oxia Palus.JPG, Huge canyons in Aureum Chaos, as seen by THEMIS. Gullies are rare at this latitude. Image from Margaritifer Sinus quadran ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Geysers On Mars
Martian geysers (or jets) are putative sites of small gas and dust eruptions that occur in the south polar region of Mars during the spring thaw. "Dark dune spots" and "spiders" – or araneiforms – are the two most visible types of features ascribed to these eruptions. Martian geysers are distinct from geysers on Earth, which are typically associated with hydrothermal activity. These are unlike any terrestrial geological phenomenon. The reflectance (albedo), shapes and unusual spider appearance of these features have stimulated a variety of hypotheses about their origin, ranging from differences in frosting reflectance, to explanations involving biological processes. However, all current geophysical models assume some sort of jet or geyser-like activity on Mars. Their characteristics, and the process of their formation, are still a matter of debate. These features are unique to the south polar region of Mars in an area informally called the 'cryptic region', at latitudes ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Pancake Dome
A pancake dome is an unusual type of lava dome found on the planet Venus. They are widely scattered on that planet and often form groups or clusters, though with smaller numbers of pancake domes in each group than is typical for the more common shield volcanos. They are commonly found near coronae and ''tesserae'' (large regions of highly deformed terrain, folded and fractured in two or three dimensions, believed to be unique to Venus) in the lowland plains. Pancake domes are between 10 and 100 times larger than volcanic domes formed on Earth. Description Pancake domes have a broad, flat profile similar to shield volcanoes and are thought to form from one large, slow eruption of viscous silica-rich lava. They usually have a central pit- or bowl-like feature similar to a volcanic crater, but it is thought that these pits form after the eruption as the lava cools and emits gas rather than being a vent from which the lava originated. The surface of pancake domes are covered with patt ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
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