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Topic Review
Vallis (Planetary Geology)
Vallis or valles /ˈvælɪs/ (plural valles /ˈvæliːz/) is the Latin word for valley. It is used in planetary geology to name landform features on other planets. Scientists used vallis for old river valleys they discovered when they sent the first probes to Mars. The Viking Orbiters caused a revolution in our ideas about water on Mars; finding huge river valleys in many areas. Space craft cameras showed that floods of water broke through dams, carved deep valleys, eroded grooves into bedrock, and traveled thousands of kilometers. Some valles on Mars (Mangala Vallis, Athabasca Vallis, Granicus Vallis, and Tinjar Valles) clearly begin at graben. On the other hand, some of the large outflow channels begin in rubble-filled low areas, called chaos or chaotic terrain. It has been suggested that massive amounts of water were trapped under pressure beneath a thick cryosphere (layer of frozen ground), then the water was suddenly released, perhaps when the cryosphere was broken by a fault.
  • 528
  • 23 Nov 2022
Topic Review
Volcanology of Mars
Volcanic activity, or volcanism, has played a significant role in the geologic evolution of Mars. Scientists have known since the Mariner 9 mission in 1972 that volcanic features cover large portions of the Martian surface. These features include extensive lava flows, vast lava plains, and the largest known volcanoes in the Solar System. Martian volcanic features range in age from Noachian (>3.7 billion years) to late Amazonian (< 500 million years), indicating that the planet has been volcanically active throughout its history, and some speculate it probably still is so today. Both Earth and Mars are large, differentiated planets built from similar chondritic materials. Many of the same magmatic processes that occur on Earth also occurred on Mars, and both planets are similar enough compositionally that the same names can be applied to their igneous rocks and minerals. Volcanism is a process in which magma from a planet's interior rises through the crust and erupts on the surface. The erupted materials consist of molten rock (lava), hot fragmental debris (tephra or ash), and gases. Volcanism is a principal way that planets release their internal heat. Volcanic eruptions produce distinctive landforms, rock types, and terrains that provide a window on the chemical composition, thermal state, and history of a planet's interior. Magma is a complex, high-temperature mixture of molten silicates, suspended crystals, and dissolved gases. Magma on Mars likely ascends in a similar manner to that on Earth. It rises through the lower crust in diapiric bodies that are less dense than the surrounding material. As the magma rises, it eventually reaches regions of lower density. When the magma density matches that of the host rock, buoyancy is neutralized and the magma body stalls. At this point, it may form a magma chamber and spread out laterally into a network of dikes and sills. Subsequently, the magma may cool and solidify to form intrusive igneous bodies (plutons). Geologists estimate that about 80% of the magma generated on Earth stalls in the crust and never reaches the surface. As magma rises and cools, it undergoes many complex and dynamic compositional changes. Heavier minerals may crystallize and settle to the bottom of the magma chamber. The magma may also assimilate portions of host rock or mix with other batches of magma. These processes alter the composition of the remaining melt, so that any magma reaching the surface may be chemically quite different from its parent melt. Magmas that have been so altered are said to be "evolved" to distinguish them from "primitive" magmas that more closely resemble the composition of their mantle source. (See igneous differentiation and fractional crystallization.) More highly evolved magmas are usually felsic, that is enriched in silica, volatiles, and other light elements compared to iron- and magnesium-rich (mafic) primitive magmas. The degree and extent to which magmas evolve over time is an indication of a planet's level of internal heat and tectonic activity. The Earth's continental crust is made up of evolved granitic rocks that developed through many episodes of magmatic reprocessing. Evolved igneous rocks are much less common on cold, dead bodies such as the Moon. Mars, being intermediate in size between the Earth and the Moon, is thought to be intermediate in its level of magmatic activity. At shallower depths in the crust, the lithostatic pressure on the magma body decreases. The reduced pressure can cause gases (volatiles), such as carbon dioxide and water vapor, to exsolve from the melt into a froth of gas bubbles. The nucleation of bubbles causes a rapid expansion and cooling of the surrounding melt, producing glassy shards that may erupt explosively as tephra (also called pyroclastics). Fine-grained tephra is commonly referred to as volcanic ash. Whether a volcano erupts explosively or effusively as fluid lava depends on the composition of the melt. Felsic magmas of andesitic and rhyolitic composition tend to erupt explosively. They are very viscous (thick and sticky) and rich in dissolved gases. Mafic magmas, on the other hand, are low in volatiles and commonly erupt effusively as basaltic lava flows. However, these are only generalizations. For example, magma that comes into sudden contact with groundwater or surface water may erupt violently in steam explosions called hydromagmatic (phreatomagmatic or phreatic) eruptions. Erupting magmas may also behave differently on planets with different interior compositions, atmospheres, and gravitational fields.
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  • 23 Nov 2022
Topic Review
Nebra Sky Disk
The Nebra sky disk is a bronze disk of around 30 centimetres (11 3⁄4 in) diameter and a weight of 2.2 kilograms (4.9 lb), having a blue-green patina and inlaid with gold symbols. These symbols are interpreted generally as the Sun or full moon, a lunar crescent, and stars (including a cluster of seven stars interpreted as the Pleiades). Two golden arcs along the sides, interpreted to mark the angle between the solstices, were added later. A final addition was another arc at the bottom surrounded with multiple strokes (of uncertain meaning, variously interpreted as a solar barge with numerous oars, the Milky Way, or a rainbow). The disk has been attributed to a site in present-day Germany near Nebra, Saxony-Anhalt, and was originally dated by archaeologists to c. 1600 BCE. Researchers initially suggested the disk is an artifact of the Bronze Age Unetice culture, although a later dating to the Iron Age has been proposed as well. If its Bronze Age dating is accurate, the Nebra sky disk features the oldest concrete depiction of the cosmos yet known from anywhere in the world. In June 2013 it was included in the UNESCO Memory of the World Register and termed "one of the most important archaeological finds of the twentieth century."
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Topic Review
Solar Team
The University of Calgary Solar Car Team is a multi-disciplinary student-run solar car racing ("raycing") team at the University of Calgary, based in Calgary, Alberta, Canada . It was established to design and build a solar car to compete internationally in the American Solar Challenge (ASC) (previously named the North American Solar Challenge) and the World Solar Challenge (WSC). The team is primarily composed of undergraduate students studying Engineering, Business, Science, Arts and Kinesiology. The mission of the University of Calgary Solar Car Team is to educate the community about sustainable energy and to serve as an interdisciplinary project through which students and faculty from various departments can collaborate in supporting sustainable energy.
  • 329
  • 23 Nov 2022
Topic Review
Stress–Energy Tensor
The stress–energy tensor, sometimes called the stress–energy–momentum tensor or the energy–momentum tensor, is a tensor quantity in physics that describes the density and flux of energy and momentum in spacetime, generalizing the stress tensor of Newtonian physics. It is an attribute of matter, radiation, and non-gravitational force fields. This density and flux of energy and momentum are the sources of the gravitational field in the Einstein field equations of general relativity, just as mass density is the source of such a field in Newtonian gravity.
  • 5.4K
  • 23 Nov 2022
Topic Review
Large UV Optical Infrared Surveyor
The Large UV Optical Infrared Surveyor (LUVOIR) is a multi-wavelength space observatory concept being developed by the Goddard Space Flight Center and proposed for the Decadal Survey Concept Study started in January 2016. The concept is based on a mirror from 8 m to 18 m in diameter, and covering the ultraviolet, visible and infrared wavelengths. It would be a Large Strategic Science Mission and be up for selection sometime after 2020. LUVOIR is a set of goals and requirements for a space telescope, but is not a specific design. More concrete proposals have their own names, such as ATLAST and HDST. One of those will be selected to become LUVOIR.
  • 418
  • 23 Nov 2022
Topic Review
Mie–Gruneisen Equation of State
The Mie–Grüneisen equation of state is a relation between the pressure and the volume of a solid at a given temperature. It is used to determine the pressure in a shock-compressed solid. The Mie–Grüneisen relation is a special form of the Grüneisen model which describes the effect that changing the volume of a crystal lattice has on its vibrational properties. Several variations of the Mie–Grüneisen equation of state are in use. The Grüneisen model can be expressed in the form where V is the volume, p is the pressure, e is the internal energy, and Γ is the Grüneisen parameter which represents the thermal pressure from a set of vibrating atoms. If we assume that Γ is independent of p and e, we can integrate Grüneisen's model to get where p0 and e0 are the pressure and internal energy at a reference state usually assumed to be the state at which the temperature is 0K. In that case p0 and e0 are independent of temperature and the values of these quantities can be estimated from the Hugoniot equations. The Mie–Grüneisen equation of state is a special form of the above equation.
  • 1.6K
  • 22 Nov 2022
Topic Review
Soyuz 1
Soyuz 1 (Russian: Союз 1, Union 1) was a crewed spaceflight of the Soviet space program. Launched into orbit on 23 April 1967 carrying cosmonaut colonel Vladimir Komarov, Soyuz 1 was the first crewed flight of the Soyuz spacecraft. The flight was plagued with technical issues, and Komarov was killed when the descent module crashed into the ground due to a parachute failure. This was the first in-flight fatality in the history of spaceflight. The original mission plan was complex, involving a rendezvous with Soyuz 2 and an exchange of crew members before returning to Earth. However, the launch of Soyuz 2 was called off due to thunderstorms.
  • 553
  • 22 Nov 2022
Topic Review
List of Asteroids in Astrology
Asteroids are relatively new to astrology, having only been discovered in the 19th century. However, some of them (especially the largest of them), are believed by some astrologers to influence human affairs. Still though, they are often ignored within mainstream systems of astrology, especially in more traditional astrology systems like Vedic astrology or Hellenistic astrology. Their use has become significant to a few Western astrologers yet still only a minority of astrologers use the asteroids in chart interpretation.
  • 4.7K
  • 22 Nov 2022
Topic Review
Volcanology of Venus
The surface of Venus is dominated by volcanic features and has more volcanoes than any other planet in the Solar System. It has a surface that is 90% basalt, and about 65% of the planet consists of a mosaic of volcanic lava plains, indicating that volcanism played a major role in shaping its surface. There are more than 1,000 volcanic structures and possible periodic resurfacing of Venus by floods of lava. The planet may have had a major global resurfacing event about 500 million years ago, from what scientists can tell from the density of impact craters on the surface. Venus has an atmosphere rich in carbon dioxide, with a density that is 90 times greater than Earth's atmosphere. Even though there are over 1,600 major volcanoes on Venus, none are known to be erupting at present and most are probably long extinct. However, radar sounding by the Magellan probe revealed evidence for comparatively recent volcanic activity at Venus's highest volcano Maat Mons, in the form of ash flows near the summit and on the northern flank. Although many lines of evidence suggest that Venus is likely to be volcanically active, present-day eruptions at Maat Mons have not been confirmed. Nevertheless, other more recent studies, in January 2020, suggests Venus is currently volcanically active.
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  • 22 Nov 2022
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