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Gusev Crater

Gusev Crater

:This article is about the crater on Mars. There is also a Gusev crater on Earth. Gusev crater Gusev Crater is a crater on the planet Mars and is located at 175.4°E 14.6°S. The crater is about 170 kilometers in diameter and formed approximately three to four billion years ago. It was named after Russian astronomer Matvei Gusev (1826–1866) in 1976. A channel system named Ma'adim Vallis drains into it that probably carried liquid water, or water and ice, at some point in Mars' past. The crater appears to be an old crater lake bed, filled with sediments up to 3000 feet thick. Some exposed outcrops appear to show faint layering, and some researchers also believe that landforms visible in images of the mouth of Ma'adim Vallis where it enters Gusev Crater resemble landforms seen in some terrestrial river deltas. Deltas of this nature can take tens or hundreds of thousands of years to form on Earth, suggesting that the water flows may have lasted for long periods. Orbital images indicate that there may once have been a very large lake near the source of Ma'adim Vallis that could have provided the source of this water. It is not known whether this flow was slow and continuous, punctuated by sporadic large outbursts, or some combination of these patterns. More recently, satellite images showed the trails of dust devils on Gusev Crater's floor. The Spirit rover later photographed dust devils from the ground, and likely owes much of its longevity to dust devils cleaning its solar panels. On January 3 2004, Gusev Crater was the landing site of the first rover in NASA's two Mars Exploration Rovers, named Spirit. It is hoped that the numerous smaller and more recent craters in this region will have exposed sedimentary material from early eras, although the region has so far proved disappointing in its lack of available bedrock for study.

Features within Gusev

- Bonneville is a 200-metre crater visited by Spirit
- The Columbia Hills is a range of low hills 3 km from Spirits original landing site; Spirit is currently exploring them
- The Apollo 1 Hills are three widely-spaced hills 7-14 km away from Spirits landing site
- Crivitz crater is a smaller crater located within Gusev
- Thira crater is a crater located within Gusev, and could be seen from the summit of Husband Hill Category:Craters on Mars

Gusev (Russian crater)

:Gusev is also the name of a crater on Mars. Gusev crater is a meteor crater in Russia. It is located near Kamensk-Shakhtinsky, Rostov Oblast. It is 3 km in diameter and the age is estimated to be 49.0 ± 0.2 million years old placing it in the Eocene. The crater is not exposed to the surface. It and the neighboring Kamensk form a double crater system.

External link

- [http://www.unb.ca/passc/ImpactDatabase/ Earth Impact Database] Category:Craters of Russia Category:Eocene craters

Impact crater

moon. NASA photo.]] An impact crater (impact basin or sometimes crater) is a circular depression on a surface, usually referring to a planet, moon, asteroid, or other celestial body, caused by a collision of a smaller body (meteorite) with the surface. In the center of craters on Earth a crater lake often accumulates, and a central island or peak (caused by rebounding crustal rock after the impact) is usually a prominent feature in the lake. Ancient craters whose relief has disappeared leaving only a "ghost" of a crater are known as palimpsests. Although it might be assumed that a major impact on the Earth would leave behind absolutely unmistakable evidence, in fact the gradual processes that change the surface of the Earth tend to cover the effects of impacts. Erosion by wind and water, deposits of wind-blown sand and water-carried sediment, and lava flows in due time tend to obscure or bury the craters left by impacts. Simple slumping of weak crustal material can also play a role, especially on outer solar system bodies such as Callisto which are covered in a crust of ice. However, some evidence remains, and over 150 major craters have been identified on the Earth. Studies of these craters have allowed geologists to find the remaining traces of other craters that have mostly been obliterated. Impact craters are found on nearly all solid surface planets and satellites. As the number of impact craters increases on a surface, the appearance of the surfaces changes; this can be used to establish the age of extraterrestrial terrain. After a period of time, however, an equilibrium is reached in which old craters are destroyed as quickly as new craters form.

History

geologists Daniel Barringer (1860-1929) was one of the first to identify a geological structure as an impact crater, the Barringer Meteorite Crater (or the "Meteor Crater") in Arizona, but at the time his ideas were not widely accepted, and when they were, there was no recognition of the fact that Earth impacts are common in geological terms. In the 1920s, the American geologist Walter H. Bucher studied a number of craters in the US. He concluded they had been created by some great explosive event, but believed they were the result of some massive volcanic eruption. However, in 1936, the geologists John D. Boon and Claude C. Albritton Jr. revisited Bucher's studies and concluded the craters he studied were probably formed by impacts. The issue remained more or less speculative until the 1960s. A number of researchers, most notably Eugene M. Shoemaker, conducted detailed studies of the craters that provided clear evidence that they had been created by impacts, identifying the shock-metamorphic effects uniquely associated with impacts, of which the most familiar is Shocked quartz. Shocked quartz Armed with the knowledge of shock-metamorphic features, Carlyle S. Beals and colleagues at the Dominion Observatory, (Victoria, British Columbia, Canada), and Wolf von Engelhardt of the University of Tübingen in Germany began a methodical search for "impact structures". By 1970, they had tentatively identified more than 50. Their work remained controversial, but the American Apollo Moon landings, which were in progress at the time, provided evidence of the rate of impact cratering on the Moon. Processes of erosion on the Moon are minimal and so craters persist almost indefinitely. 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. The age of known impact craters on the Earth ranges from about a thousand (e.g. the Haviland crater in Kansas) to almost two billion years, though few older than 200 million years have been found, as geological processes tend to obliterate older ones. They are also selectively found in the stable interior regions of continents. Few underwater 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 the Earth's interior by processes of plate tectonics. Current estimates of the rate of cratering on the Earth suggest that from one to three craters with a width greater than 20 kilometers are created every million years. This indicates that there are far more relatively young craters on the planet than have been discovered so far.

Formation and structure

An object falling from open space hits the Earth with a minimum velocity of 11.6 km/s (7 mi/s). Since the energy from motion grows as the square of the velocity, this gives moving rock more energy per kilogram than ordinary chemical explosives. Massive objects can easily cause kiloton explosions that resemble nuclear explosions. Seismographs record about one multikiloton impact somewhere on the Earth each year, usually in mid-ocean. If the object weighs more than 1,000 tonnes, an atmosphere does not slow it down much, though smaller bodies can be substantially slowed by atmospheric drag, as they have a higher ratio of surface area to mass. In any case, the temperatures and pressures on the object are extremely high. These temperature and pressure extremes can destroy chondritic or carbonaceous chondritic bodies before they ever reach ground, but metallic iron-nickel meteorites have more structural integrity and can strike the surface of the Earth in a violent explosion. When the object hits, it compresses a column of air, water and rock into an extremely hot plasma. This plasma expands violently, and cools rapidly (i.e. it explodes). The plasma and other ejecta splashes at orbital or near-orbital speeds. It can be thrown off into space, or can travel several times around the planet before re-entering as secondary meteors. Airless planets usually preserve stains of the ejecta around impact craters as a pattern of "rays". It should be noted that other non-impact theories for crater-ray formation have been suggested in the scientific literature. plasma Very energetic chemistry occurs in the plasma. In an Earth impact, powerful acids can be formed from saltwater and air. The vaporized rock of the plasma condenses into characteristic cone-shaped droplets of glass called tektites, and these are widely distributed by the high speeds. Tektites are found in isolated strewnfields on Earth. Note: Several researchers reject the popular impact-origin theory of tektites based on comparisons to bonafide impactite glasses. Curiously, the largest and youngest (700,000 years ago) tektite strewnfield, known as the Australasian field, has no known crater associated with it; this fact strongly suggests that, at least in this case, the tektites are not linked to an impact. A giant "fresh" impact site, less than a million years old, should be visible on land or in the sea. No such Asian impact crater has ever been found.. Oceanic impacts can be considerably more damaging than those on land. Large objects will invariably penetrate or displace the water to impact the seabed, causing huge tsunamis over a large area. The impact at Chicxulub, Yucatán is believed to have produced tsunamis 50 to 100 metres (150-300 feet) high which deposited debris many miles inland. The result of an impact on land or at sea is a crater. There are two forms, "simple" and "complex". The Barringer crater in Arizona is a perfect example of a simple crater, a straightforward bowl in the ground. Simple craters are generally less than four kilometers across. Complex craters are larger, and have uplifted centers that are surrounded by a trough, plus broken rims. The uplifted center is due to the "rebound" of the earth after the impact. It is something like the ripple pattern created by a drop of water into a pool, frozen into the Earth when the melted rock cooled and solidified. Arizona In either case, the size of the crater depends on the size of the impactor and the material in the impact regions. Relatively soft materials yield smaller craters than brittle materials. The size of craters invariably changes over time; in the short term, craters shrink as a result of slumping, and over the longer term erosion and other geological processes quickly hide impact craters on the Earth. The Barringer Crater is one of the best-preserved on the planet, but it is only about 50,000 years old. There are almost no signs of the 65 million year-old Chicxulub crater on the Earth's surface, despite it being one of the largest known on the planet. Some volcanic features can resemble impact craters, and brecciated rocks are associated with other geological formations besides impact craters. Non-explosive volcanic craters can usually be distinguished from impact craters by their irregular shape and the association of volcanic flows and other volcanic materials. An exception is that impact craters on Venus often have associated flows of melted material. 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 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:
- A layer of shattered or "brecciated" rock under the floor of the crater. This layer is called a "breccia lens".
- Shatter cones, which are chevron-shaped impressions in rocks. Such cones are formed most easily in fine-grained rocks.
- High-temperature rock types, including laminated and welded blocks of sand, and tektites, or glassy spatters of molten rock. The impact origin of tektites has been questioned by some researchers; they have observed some volcanic features in tektites not found in impactites. Tektites are also drier (contain less water) than typical impactites. While rocks melted by the impact resemble volcanic rocks, they incorporate unmelted fragments of bedrock, form unusually large and unbroken fields, and have a much more mixed chemical composition than volcanic materials spewed up from within the Earth. They also may have relatively large amounts of trace elements that are associated with meteorites, such as nickel, platinum, iridium, and cobalt. Note: it is reported in the scientific literature that some "shock" features, such as small shatter cones, which are often reported as being associated only with impact events, have been found in terrestrial volcanic ejecta.
- Microscopic pressure deformations of minerals. These include fracture patterns in crystals of quartz and feldspar, and formation of high-pressure materials such as diamond, derived from graphite and other carbon compounds, or stishovite and coesite, varieties of shocked quartz. Craters can also be created from underground nuclear explosions. One of the most crater-pocked sites on the planet is the Nevada Test Site, where a number of craters were purposely made during its years as a center for nuclear testing (see, for example, Operation Plowshare).

Crater categorization

In 1978, Chuck Wood and Leif Andersson of the Lunar & Planetary Lab devised a system of categorization of lunar impact craters. They used a sampling of craters that were relatively unmodified by subsequent impacts, then grouped the results into five broad categories. These successfully accounted for about 99% of all lunar impact craters. The LPC Crater Types were as follows:
- ALC — small, cup-shaped craters with a diameter of about 10 km or less, and no central floor. The archetype for this category is 'Albategnius C'.
- BIO — similar to an ALC, but with small, flat floors. Typical diameter is about 15 km. The lunar crater archetype is Biot.
- SOS — the interior floor is wide and flat, with no central peak. The inner walls are not terraced. The diameter is normally in the range of 15-25 km. The archetype is Sosigenes crater.
- TRI — these complex craters are large enough so that their inner walls have slumped to the floor. They can range in size from 15-50 km in diameter. The archetype crater is Triesnecker.
- TYC — these are larger than 50 km, with terraced inner walls and relatively flat floors. They frequently have large central peak formations. Tycho crater is the archetype for this class. Beyond a couple of hundred kilometers diameter, the central peak of the TYC class disappear and they are classed as basins.

Lists of craters

Notable impact craters on Earth

- Barringer Crater (US)
- Carolina bays (Eastern US)
- Chesapeake Bay impact crater (Eastern US)
- Chicxulub Crater (Mexico)
- Haughton impact crater (Canada)
- Lonar crater (India)
- Mahuika crater (New Zealand)
- Manicouagan Reservoir (Canada)
- Manson crater (US)
- Mistastin crater (Canada)
- Nördlinger Ries (Germany)
- Panther Mountain New York, (US)
- Rochechouart crater (France)
- Sudbury Basin (Canada)
- Silverpit crater (United Kingdom, located in the North Sea)
- Rio Cuarto craters (Argentina)
- The Siljan Ring (Sweden)
- Vredefort crater (Vredefort, South Africa)
- Weaubleau-Osceola impact structure (Central US)
- Kaali crater (Estonia) See the [http://www.unb.ca/passc/ImpactDatabase/essay.html Earth Impact Database,] a website concerned with over 160 identified impact craters on the Earth.

Some extraterrestrial craters

- Caloris Basin (Mercury)
- Hellas Basin (Mars)
- Mare Orientale (Moon)
- Petrarch crater (Mercury)
- South Pole-Aitken basin (Moon)
- Herschel crater (Mimas)

References

- Charles A. Wood and Leif Andersson, [http://adsabs.harvard.edu//full/seri/LPSC./0009//0003669.000.html New Morphometric Data for Fresh Lunar Craters], 1978, Procedings 9th Lunar and Planet. Sci. Conf.

External links

- [http://planetscapes.com/solar/eng/tercrate.htm Photographs of terrestrial impact craters.]
- [http://scsn.seis.sc.edu/Publications/GRLFinalDraft(web).pdf a study of a South Carolina crater]
- [http://www.unb.ca/passc/ImpactDatabase/CIDiameterSort.html The Geological Survey of Canada Crater database, 172 impact structures]
- [http://www.spacedaily.com/news/deepimpact-02k.html A recent news report about tektites]
- [http://www.ottawa.rasc.ca/astronomy/earth_craters/index.html Aerial Explorations of Terrestrial Meteorite Craters]
- [http://bbs.keyhole.com/ubb/download.php?Number=71111 Google Earth Placemarker based on the Geological Survey of Canada Crater database] Category:Craters
- Category:Planetary science Category:Depressions ko:크레이터 ja:クレーター

Mars/Planet

Mars, the fourth planet from the Sun in our solar system, is named after the Roman god of war Mars (Ares in Greek mythology), because of its apparent red color. This feature also earned it the nickname "The Red Planet". Mars has two moons, Phobos and Deimos, which are small and oddly-shaped, possibly being captured asteroids. The prefix areo- refers to Mars in the same way geo- refers to Earth—for example, areology versus geology. (However, areology is also used to refer to the study of Mars as a whole rather than just the geological processes of the planet.) The astronomical symbol for Mars is a circle with an arrow pointing northeast (Unicode: ♂). This symbol is a stylized representation of the shield and spear of the god Mars, and in biology it is used as a sign for the male sex. The Chinese, Korean, Japanese, and Vietnamese cultures refer to the planet as the fire star, 火星, a naming based on the ancient Chinese mythological cycle of Five Elements.

Mythology

Mars has been obvious to skygazers since prehistoric times. It was known by the Egyptians as "Her Deschel" or "the Red One." Among the Babylonians Mars was known as "Nergal" or "the Star of Death." The Romans were the ones to give Mars its modern name, after their god of war.

Physical characteristics

The red, fiery appearance of Mars is caused by iron oxide (rust) on its surface. Mars has only a quarter the surface area of the Earth and only one-tenth the mass, though its surface area is approximately equal to that of the Earth's dry land because Mars lacks oceans. The solar day (or sol) on Mars is very close to Earth's day: 24 hours, 39 minutes, and 35.244 seconds.

Atmosphere

Mars' atmosphere is thin: the air pressure on the surface is only 750 pascals, about 0.75% of the average on Earth. However, the scale height of the atmosphere is about 11 km, somewhat higher than Earth's 6 km. The atmosphere on Mars is 95% carbon dioxide, 3% nitrogen, 1.6% argon, and contains traces of oxygen and water. The atmosphere quite dusty, giving the Martian sky a tawny color when seen from the surface; data from the Mars Exploration Rovers indicates the suspended dust particles are roughly 1.5 microns across. In 2003, methane was apparently discovered in the atmosphere by Earth-based telescopes and possibly confirmed in March 2004 by the Mars Express Orbiter; present measurements state an average methane concentration of about 11±4 ppb by volume (see reference). The thin atmosphere cannot hold heat and is the cause of the lower temperatures on Mars. The maximum temperature is roughly 20℃ (68℉). The presence of methane on Mars would be very intriguing, since as an unstable gas it indicates that there must be (or have been within the last few hundred years) a source of the gas on the planet. Volcanic activity, comet impacts, and the existence of life in the form of microorganisms such as methanogens are among possible but as yet unproven sources. The methane appears to occur in patches, which suggests that it is being rapidly broken down before it has time to become uniformly distributed in the atmosphere, and so it is presumably also continually being released to the atmosphere. Plans are now being made to look for other companion gases that may suggest which sources are most likely; in the Earth's oceans biological methane production tends to be accompanied by ethane, while volcanic methane is accompanied by sulfur dioxide. Other aspects of the Martian atmosphere vary significantly. In the winter months when the poles are in continual darkness, the surface gets so cold that as much as 25% of the entire atmosphere condenses out into meters thick slabs of CO₂ ice (dry ice). When the poles are again exposed to sunlight the CO₂ ice sublimates, creating enormous winds that sweep off the poles as fast as 250 mph. These seasonal actions transport large amounts of dust and water vapor giving rise to Earth-like frost and large cirrus clouds. These clouds of water-ice were photographed by the Opportunity rover in 2004.[http://marsrovers.jpl.nasa.gov/gallery/press/opportunity/20041213a/merb_sol290_clouds-B313R1_br.jpg] Recently, evidence has been discovered suggesting that Mars may be warming in the short term[http://news.bbc.co.uk/2/hi/science/nature/4266474.stm]; however, it is now cooler than it was in the 1970s.[http://catdynamics.blogspot.com/2005/09/climate-science-mars-and-politics.html]

Geology

Opportunity The surface of Mars is thought to be primarily composed of basalt, based upon the Martian meteorite collection and orbital observations. There is some evidence that some portion of the Martian surface might be more silica-rich than typical basalt, perhaps similar to andesitic rocks on Earth, though these observations may also be explained by silica glass. Much of the surface is deeply covered by dust as fine as talcum powder. Observations of the magnetic fields on Mars by the Mars Global Surveyor spacecraft have revealed that parts of the planet's crust has been magnetized. This magnetization has been compared to alternating bands found on the ocean floors of Earth. One interesting theory, published in 1999 and reexamined in October 2005 in a publication by the same group, is that these bands could be evidence of the past operation of plate tectonics on Mars. However, this has yet to be proven [http://photojournal.jpl.nasa.gov/catalog/PIA02008] or widely accepted and remains an area of active research. plate tectonics Amongst the findings from the Opportunity rover is the presence of hematite on Mars in the form of small spheres on the Meridiani Planum. The spheres are only a few millimeters in diameter and are believed to have formed as rock deposits under watery conditions billions of years ago. Other minerals have also been found containing forms of sulfur, iron or bromine such as jarosite. This and other evidence led a group of 50 scientists to conclude in the December 9, 2004 edition of the journal Science that "Liquid water was once intermittently present at the Martian surface at Meridiani, and at times it saturated the subsurface. Because liquid water is a key prerequisite for life, we infer conditions at Meridiani may have been habitable for some period of time in Martian history". On the opposite side of the planet the mineral goethite, which (unlike hematite) forms only in the presence of water, along with other evidence of water, has also been found by the Spirit rover in the "Columbia Hills". In 1996, researchers studying a meteorite (ALH84001) believed to have originated from Mars reported features which they attributed to microfossils left by life on Mars. As of 2005, this interpretation remains controversial with no consensus having emerged.
Topography
As of 2005 As of 2005 The dichotomy of Martian topography is striking: northern plains flattened by lava flows contrast with the southern highlands, pitted and cratered by ancient impacts. The surface of Mars as seen from Earth is consequently divided into two kinds of areas, with differing albedo. The paler plains covered with dust and sand rich in reddish iron oxides were once thought of as Martian 'continents' and given names like Arabia Terra (land of Arabia) or Amazonis Planitia (Amazonian plain). The dark features were thought to be seas, hence their names Mare Erythraeum, Mare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major. Syrtis Major Mars has polar ice caps that contain frozen water and carbon dioxide that change with the Martian seasons — the carbon dioxide ice sublimates in summer it uncovers an underlying surface of layered water ice and dust. The polar carbon dioxide "hood" then forms again in winter. The supposedly-extinct shield volcano, Olympus Mons (Mount Olympus), is at 26 km the highest mountain in the solar system. It is in a vast upland region called Tharsis, which contains several large volcanos. See list of mountains on Mars. Mars also has the solar system's largest canyon system, Valles Marineris or the Mariner Valley, which is 4000 km long and 7 km deep. Mars is also scarred by a number of impact craters. The largest of these is the Hellas impact basin, covered with light red sand. See list of craters on Mars. The difference between Mars' highest and lowest points is nearly 31 km (from the top of Olympus Mons at an altitude of 26 km to the bottom of the Hellas impact basin at an altitude of 4 km below the datum). In comparison, the difference between Earth's highest and lowest points (Mount Everest and the Mariana Trench) is only 19.7 km. Combined with the planets' different radii, this means Mars is nearly three times "rougher" than Earth. The International Astronomical Union's Working Group for Planetary System Nomenclature is responsible for naming Martian surface features. Other notes: Zero elevation: Since Mars has no oceans and hence no 'sea level', a zero-elevation surface or mean gravity surface must be selected. The datum for Mars is defined by the fourth-degree and fourth-order spherical harmonic gravity field, with the zero altitude defined by the 610.5 Pa (6.105 mbar) atmospheric pressure surface (approximately 0.6% of Earth's) at a temperature of 273.16 K. This pressure and temperature correspond to the triple point of water. Zero meridian: Mars' equator is defined by its rotation, but the location of its Prime Meridian was specified, as was Earth's, by choice of an arbitrary point which was accepted by later observers. The German astronomers Wilhelm Beer and Johann Heinrich Mädler selected a small circular feature as a reference point when they produced the first systematic chart of Mars features in 1830-32. In 1877, their choice was adopted as the prime meridian by the Italian astronomer Giovanni Schiaparelli when he began work on his notable maps of Mars. After the spacecraft Mariner 9 provided extensive imagery of Mars in 1972, a small crater (later called Airy-0), located in the Sinus Meridiani ('Middle Bay' or 'Meridian Bay') along the line of Beer and Mädler, was chosen by Merton Davies of the RAND Corporation to provide a more precise definition of 0.0° longitude when he established a planetographic control point network. RAND Corporation
Canals
Mars has an important place in human imagination due to the belief by some that life existed on Mars. These beliefs are due mainly to observations by many in the 19th century popularized by Percival Lowell and Giovanni Schiaparelli. Schiaparelli called these observed features canali, meaning channels in Italian. This was popularly mistranslated as 'canals', and the myth of the Martian canals began. They were apparently artificial linear features on the surface that were asserted to be canals, and due to seasonal changes in the brightness of some areas that were thought to be caused by vegetation growth. This gave rise to many stories concerning Martians. The linear features are now known to be mostly non-existent or, in some cases, dry ancient watercourses. The color changes have been ascribed to dust storms.
Ice lakes
many stories On 29 July 2005, the BBC reported that a visible ice lake had been discovered in a crater in the north polar region of Mars[http://news.bbc.co.uk/1/hi/sci/tech/4727847.stm]. Images of the crater, taken by the High Resolution Stereo Camera on board the European Space Agency's Mars Express spacecraft, clearly show a broad sheet of ice in the bottom of an unnamed crater located on Vastitas Borealis, a broad plain that covers much of Mars' far northern latitudes, at approximately 70.5° North and 103° East. The crater is 35 km (23 mi) wide and about 2 km (1.2 mi) deep. The BBC report however, appears to have either intentionally sensationalized or unintentionally mis-interpreted the original HRSC/Mars Express feature[http://www.esa.int/SPECIALS/Mars_Express/SEMGKA808BE_0.html], which makes no claim or insinuation that this is a "lake". Like many thousands of other places on Mars, this ice sheet is a thin layer of frost that has condensed onto dark, cold sand dunes (about 200 m high) making their way across the bottom of the crater. The only thing remarkable about this feature is that it is far enough north to maintain at least some frost throughout the year.
The moons of Mars
Mars has two tiny natural moons, Phobos and Deimos, which orbit very close to the planet and are thought to be captured asteroids.
The exploration of Mars
asteroid Dozens of spacecraft, including orbiters, landers, and rovers, have been sent to Mars by the Soviet Union, the United States, Europe, and Japan to study the planet's surface, climate, and geography. Roughly two-thirds of all spacecraft destined for Mars have failed in one manner or another before completing or even beginning their missions. Part of this high failure rate can be ascribed to technical problems, but enough have either failed or lost communications for no apparent reason that some researchers half-jokingly speak of an Earth-Mars "Bermuda Triangle" or of a Great Galactic Ghoul which subsists on a diet of Mars probes, or of a Mars Curse. Among the most successful missions are the Mars probe program, the Mariner and Viking programs, Mars Global Surveyor, Mars Pathfinder, and Mars Odyssey. Global Surveyor has taken pictures of gullies and debris flow features that suggest there may be current sources of liquid water, similar to an aquifer, at or near the surface of the planet. Another possible origin proposed for these gully features is transient melting of surface water snow, frost, or ice. Mars Odyssey determined that there are significant deposits of water ice in the upper meter or so of Mars' regolith within 30° of the north and south pole. In 2003, the ESA launched the Mars Express craft consisting of the Mars Express Orbiter and the lander Beagle 2. Attempts to contact the Beagle 2 failed and it was declared lost in early February 2004. Beagle 2 Also in 2003, NASA launched the twin Mars Exploration Rovers named Spirit (MER-A) and Opportunity (MER-B). Both missions landed successfully in January 2004 and have met or exceeded all their targets; while a 90-day nominal mission was planned, as of February 2005, their missions have been extended twice and they continue to return science, although some mechanical faults have occurred. Among the most significant science return has been evidence of liquid water some time in the past at both landing sites. In addition, dust devils imaged from ground-level have been detected moving across the surface of Mars by Spirit (MER-A). (See picture below). Dust devils were first imaged on Mars from the surface by Mars Pathfinder. Mars Pathfinder
Nomenclature

Early nomenclature
Although better remembered for mapping the Moon starting in 1830, Johann Heinrich Mädler and Wilhelm Beer were the first "areographers". They started off by establishing once and for all that most of the surface features were permanent, and pinned down Mars' rotation period. In 1840, Mädler combined ten years of observations and drew the first map of Mars ever made. Rather than giving names to the various markings they mapped, Beer and Mädler simply designated them with letters; Meridian Bay (Sinus Meridiani) was thus feature "a". Over the next twenty years or so, as instruments improved and the number of observers also increased, various Martian features acquired a hodge-podge of names. To give a couple of examples, Solis Lacus was known as the "Oculus" (the Eye), and Syrtis Major was usually known as the "Hourglass Sea" or the "Scorpion". In 1858, it was also dubbed the "Atlantic Canale" by the Jesuit astronomer Angelo Secchi. Secchi commented that it "seems to play the role of the Atlantic which, on Earth, separates the Old Continent from the New" —this was the first time the fateful canale, which in Italian can mean either "channel" or "canal", had been applied to Mars. In 1867, Richard Anthony Proctor drew up a map of Mars based, somewhat crudely, on the Rev. William Rutter Dawes' earlier drawings of 1865, then the best ones available. Proctor explained his system of nomenclature by saying, "I have applied to the different features the names of those observers who have studied the physical peculiarities presented by Mars." Here are some of his names, paired with those later proposed by Schiaparelli:
- Kaiser Sea = Syrtis Major1865
- Lockyer Land = Hellas
- Main Sea = Lacus Moeris
- Herschel II Strait = Sinus Sabaeus
- Dawes Continent = Aeria and Arabia
- De La Rue Ocean = Mare Erythraeum
- Lockyer Sea = Solis Lacus
- Dawes Sea = Tithonius Lacus
- Madler Continent = Chryse, Ophir, Tharsis
- Maraldi Sea = Mares Sirenum and Cimmerium
- Secchi Continent = Memnonia
- Hooke Sea = Mare Tyrrhenum
- Cassini Land = Ausonia
- Herschel I Continent = Zephyria, Aeolis, Aethiopis
- Hind Land = Libya Proctor's nomenclature has often been criticized, mainly because so many of his names honored English astronomers, but also because he used many names more than once. In particular, Dawes appeared no fewer than six times (Dawes Ocean, Dawes Continent, Dawes Sea, Dawes Strait, Dawes Isle, and Dawes Forked Bay). Even so, Proctor's names are not without charm, and for all their shortcomings they were a foundation on which later astronomers would improve.
Modern nomenclature
Today, features on Mars derive from a number of sources. Large albedo features retain many of the older names, but are often updated to reflect new knowledge of the nature of the features. For example 'Nix Olympica' (the snows of Olympus) has become 'Olympus Mons' (Mount Olympus). Large Martian craters are named after important scientists and science fiction writers; smaller ones are named after towns and villages on Earth.
Observation of Mars
Earth passes Mars every 780 days (or two years plus seven weeks and one day) at a distance of about 80,000,000 km. However, this varies because the orbits are elliptical. To a naked-eye observer, Mars usually shows a distinct yellow, orange or reddish colour, and varies in brightness more than any other planet as seen from Earth over the course of its orbit, due to the fact that when furthest away from the Earth it is more than seven times as far from the latter as when it is closest (and can be lost in the Sun's glare for months at a time when least favourably positioned). At its most favourable times — which occur twice every 32 years, alternately at 15 and 17-year intervals, and always between late July and late September — Mars shows a wealth of surface detail to a telescope. Especially noticeable, even at low magnification, are the polar ice caps. polar ice cap On August 27, 2003, at 9:51:13 UT, Mars made its closest approach to Earth in nearly 60,000 years: 55,758,006 km (approximately 35 million miles) without Light-time correction. This close approach came about because Mars was one day from opposition and about three days from its perihelion, making Mars particularly easy to see from Earth. The last time it came so close is estimated to have been on September 12, 57,617 BC. Detailed analysis of the solar system's gravitational landscape forecasts an even closer approach in 2287. However, to keep this in perspective, this record approach was only an imperceptibly tiny fraction less than other recent close approaches that occur four times every 284 years. For instance, the minimum distance on August 22 1924 was 0.37284 AU, compared to 0.37271 AU on August 27 2003, and the minimum distance on August 24 2208 will be 0.37278 AU. A transit of the Earth as seen from Mars will occur on November 10, 2084. At that time the Sun, the Earth and Mars will be exactly in a line. There are also transits of Mercury and transits of Venus, and the moon Deimos is of sufficiently small angular diameter that its partial "eclipses" of the Sun are best considered transits (see Transit of Deimos from Mars). The only occultation of Mars by Venus to be observed was that of October 3, 1590, seen by M. Möstlin at Heidelberg. Heidelberg
Appearance

Martian meteorites
:Main article: Martian meteorites A handful of objects are known that are surely meteorites and may be of Martian origin. Two of them may show signs of ancient bacterial activity. On August 6, 1996 NASA announced that analysis of the ALH 84001 meteorite thought to have come from Mars, shows some features that may be fossils of single-celled organisms, although this idea is controversial. In Solar System Research (March 2004, vol 38, page 97) it was suggested that the unique Kaidun meteorite, recovered from Yemen, may have originated on the Martian moon of Phobos. On April 14, 2004, NASA revealed that a rock known as "Bounce", studied by the Mars Exploration Rover Opportunity, was similar in composition to the meteorite EETA79001-B, discovered in Antarctica in 1979. The rock may have been ejected from the same crater as the meteorite, or from another crater in the same area of the Martian surface.
Life on Mars
Evidence exists that the planet once was significantly more habitable than today, but the question whether living organisms ever actually existed there is an open one. Some researchers think that a certain rock which is believed to have originated on Mars - specifically, meteorite ALH84001 - does contain evidence of past biologic activity, but no consensus about these claims has been achieved so far and recent research indicates that the rock, since its creation several billion years ago, has never been exposed to temperatures for extended periods of time that would allow for liquid water. The Viking probes carried experiments designed to detect microorganisms in Martian soil at their respective landing sites, and had some positive results, later denied by many scientists, resulting in ongoing controversy. Also, present biologic activity is one of the explanations that have been suggested for the presence of traces of methane within the Martian atmosphere, but other explanations not involving life are generally considered more likely. If colonization is going to happen, Mars seems a likely choice due to its rather hospitable conditions (compared with other planets, it is most like Earth).
The Mars flag
colonization In early 2000, a proposed Mars flag flew aboard the space shuttle Discovery. Designed by NASA engineer and Flashline Mars Arctic Research Station task force leader Pascal Lee and carried aboard by astronaut John Mace Grunsfeld, the flag consists of three vertical bars (red, green, and blue), symbolizing the transformation of Mars from a barren planet (red) to one bearing sustainable life (green), and finally to a fully terraformed planet with open bodies of water. This design was suggested by the Kim Stanley Robinson sci-fi trilogy Red Mars, Green Mars, and Blue Mars. While other designs have been proposed, the republican tricolor has been adopted by the Mars Society as its own official banner. In a statement released after the launch of the mission, the Society said that the flag "has now been honored by a vessel of the leading spacefaring nation on Earth," and added that "(i)t is fitting that this action occurred when it did: at the dawning of a new millenium."
Mars in fiction
The depiction of Mars in fiction has been stimulated its dramatic red color and by early scientific speculations that its surface conditions might be capable of supporting life. Until the arrival of planetary probes, the traditional view of Mars derived from the astronomers Percival Lowell and Giovanni Schiaparelli, whose observation of supposedly linear features on the planet created the myth of canals on Mars. For many years, a standard notion of the planet as a drying, cooling, dying world with ancient civilizations constructing irrigation works. Thus originated a large number of science fiction scenarios, the best known of which is H. G. Wells' The War of the Worlds, in which Martians seek to escape their dying planet by invading Earth. After the Mariner and Viking spacecraft had returned pictures of Mars as it really is, an apparently lifeless and canal-less world, these ideas about Mars had to be abandoned and a vogue for accurate, realist depictions of human colonies on Mars developed, the best known of which may be Kim Stanley Robinson's Mars trilogy. However, pseudo-scientific speculations about the Face on Mars and other enigmatic landmarks spotted by space probes have meant that ancient civilizations continue to be a popular theme in science fiction, especially in film. Another popular theme, particularly among American writers, is the Martian colony that fights for independence from Earth. This is a major plot element in the novels of Greg Bear and Kim Stanley Robinson, as well as the movie Total Recall (based on a novel by Philip K. Dick) and the television series Babylon 5. Many video games also use this element, such as Red Faction.
See also

- Areography
- Astrobiology
- Astronomy on Mars
- Colonization of Mars
- Darian calendar
- Face on Mars photo article
- Timekeeping on Mars
- Exploration of Mars
- List of artificial objects on Mars
- List of craters on Mars
- List of mountains on Mars
- Martian meteorite
- Mars photos
- Mars in fiction
- Extraterrestrial life
- Terraforming
- Mars Direct
- Mars in astrology
- Ares
- Tyr
- Richard C. Hoagland
References

- William Sheehan, [http://www.uapress.arizona.edu/onlinebks/mars/contents.htm The Planet Mars: A History of Observation and Discovery], The University of Arizona Press, Tucson, 1996
- Vladimir A. Krasnopolsky, Jean-Pierre Maillard, Tobias C. Owen, [http://www.google.ca/url?sa=U&start=1&q=http://www.cosis.net/abstracts/EGU04/06169/EGU04-A-06169.pdf&e=912 Detection of methane in the Martian atmosphere: evidence for life?], Icarus, 172 (2), 537-547. [http://adsabs.harvard.edu/cgi-bin/nph-bib_query?bibcode=2004Sci...306.1753L&db_key=AST&data_type=HTML&format=&high=439c7b95b425777 Lemmon et al., "Atmospheric Imaging Results from the Mars Exploration Rovers: Spirit and Opportunity"]
External links

- [http://nssdc.gsfc.nasa.gov/planetary/factsheet/marsfact.html NASA's Mars fact sheet]
- [http://www.nineplanets.org/mars.html Nine Planets Mars page]
- [http://www.marsnews.com MarsNews.com - News and info site]
- [http://www.student.oulu.fi/~jkorteni/space/mars/surface/ Introduction to Martian topography, with Hubble Space Telescope photos]
- [http://www.geoinf.fu-berlin.de/mex/ FU Berlin: HRSC (camera) experiment at Mars Express] (eng. & ger.; press releases and high resolution images)
- [http://www.giss.nasa.gov/tools/mars24/help/notes.html Technical Notes about Time on Mars]
- [http://history.nasa.gov/SP-4212/on-mars.html On Mars: Exploration of the Red Planet 1958-1978] from the NASA History Office.
- [http://flagspot.net/flags/mars.html The Mars Society flag]
- [http://www.vias.org/spacetrip/mars_globalview.html A Trip Into Space] Photos and descriptions of Mars
- [http://www.cato.org/pubs/wtpapers/980815paper.html Martian Law - a CATO white paper]
- [http://www.marsunearthed.com/ Mars Unearthed] - Comparisons of terrains between Earth and Mars
- [http://www.ibiblio.org//e-notes/VRML/Globe/Globe.htm 3D VRML Mars globe]
- [http://www.enterprisemission.com/ Enterprise Mission: Richard C. Hoagland's Homepage]
Water on Mars

- [http://news.bbc.co.uk/1/hi/sci/tech/4727847.stm Highly visible ice lake found on Mars - BBC]
- Dr. Tony Phillips: [http://science.nasa.gov/headlines/y2000/ast29jun_1m.htm "Making a Splash on Mars"], Science@NASA article, June 29, 2000. Phillips describes the Martian "gullies" and explains the conditions under which liquid water can exist on the surface of Mars.
- [http://news.bbc.co.uk/hi/english/sci/tech/newsid_2009000/2009318.stm BBC News story on subsurface ice deposits on Mars]
- [http://news.bbc.co.uk/1/hi/sci/tech/3426539.stm BBC News update on Mars Express' findings of polar water ice and water-eroded features on the surface]
- [http://www.nasa.gov/vision/universe/solarsystem/opportunity_water.html Mars Rover Scientists Wring Water Story from Rocks] This image taken by Mars Rover Opportunity shows microscopic rock forms indicating past signs of water. Courtesy: NASA
- [http://news.bbc.co.uk/1/hi/sci/tech/4285119.stm BBC News Mars pictures reveal frozen sea]
Mars exploration

- [http://www.transhumanist.com/volume4/space.htm The Political Economy of Very Large Space Projects (Journal Of Evolution and Technology)]
- [http://www.exploremarsnow.org/ exploreMarsnow] Interactive Mars base simulation. Winner of 2003 Webby Award for Science.
- [http://marsrovers.jpl.nasa.gov/home/index.html NASA Mars Exploration Rover Home Page]
- [http://dualmoments.com/marsrovers/index.html Be on Mars] Anaglyphs from the Mars Rovers (3D)
- als:Mars (Planet) ko:화성 ms:Marikh ja:火星 simple:Mars (planet) th:ดาวอังคาร

Matvei Gusev

Matvei Matveevich Gusev (Матвей Матвеевич Гусев) (1826 (Vyatka, Russia) – 1866 (Berlin, Germany)) was a Russian astronomer who worked at Pulkovo Observatory near St. Petersburg from 1850–1852 and then at Vilnius Observatory (which he established at the University of Vilnius) thereafter. He was first to prove the non-sphericity of the Moon, concluding that it is elongated in the direction of the Earth. In 1860 he founded the first scientific journal dedicated to math and physics in Russia: Vestnik matematicheskikh nauk (Вестник математических наук). A major crater on Mars is named Gusev crater after him, and it is famed as the landing site of the Mars Exploration Rover Spirit. He is considered one of the pioneers in using photography in astronomy, having taken pictures of the moon and the sun - including subspots - while at the Vilnius observatory. He became the director of the Vilnius Observatory in 1865. He died in Berlin, Germany in 1866. Gusev, Matvei Gusev, Matvei Gusev, Matvei

Ma'adim Vallis

Ma'adim Vallis is one of the largest canyons on Mars, about 700 kilometers long and significantly larger than Earth's Grand Canyon. It is over 20 kilometers wide and 2 kilometers deep in some places. It runs from a region of southern lowlands thought to have once contained a large group of lakes north to Gusev crater near the equator. Ma'adim Vallis is thought to have been carved by flowing water early in Mars' history. Some of the short narrow channels along the walls of Ma'adim are probably sapping channels. Sapping occurs when groundwater partially dissolves and undermines the rock, which collapses into debris deposits and is carried away by other erosion processes. Ma'adim (מאדים) is the Hebrew name of the Planet Mars. Category:Topography of Mars Category:Canyons

Crater Lake

__NOTOC__ :For the general term of a geological feature that goes by the same name, see crater lake. crater lake Crater Lake is a lake in the U.S. state of Oregon that is 5 by 6 miles (8 by 9.6 km) and 1958 ft (597 m) deep. It is Crater Lake National Park's most prominent feature and is famous for its deep blue color, water clarity and vertical driftwood, named Old Man of the Lake. The lake partly fills a nearly 4000 ft (1220 m) deep caldera that was formed around 6900 years ago by the collapse of the volcano Mount Mazama. Mount Mazama The lake's average depth is around 1500 ft (450 m). Its deepest point has been measured at 1932 ft (589 m) deep, though as with any lake its depth fluctuates with the climate, particularly rainfall [http://soundwaves.usgs.gov/2000/09/fieldwork.html]. This makes Crater Lake the deepest lake in the United States, the second deepest lake in the Western Hemisphere (Great Slave Lake is first) and the seventh deepest lake in the world (Lake Baikal is first). The caldera rim ranges in elevation from 7000 to 8000 ft (2130 to 2440 m). The Oregon state quarter, released in 2005, features an image of Crater Lake. 2005 2005

Geology

2005 For more detail, see Mount Mazama. The caldera was created in a massive volcanic eruption that lead to the subsidence of Mount Mazama around 4860 BC. Since that time, all eruptions on Mazama have been confined to the caldera. Lava eruptions later created a central platform, Wizard Island, Merriam Cone, and other, smaller volcanic features, including a rhyodacite dome that was eventually created atop the central platform. Sediments and landslide debris also covered the caldera floor. In time, the caldera cooled, allowing rain and snow to accumulate and eventually form a lake. Landslides from the caldera rim thereafter formed debris fans and turbidite sediments on the lakebed. Fumaroles and hot springs remained common and active during this time. In time, the slopes of the caldera rim more or less stabilized, streams restored a radial drainage pattern on the mountain, and dense forests revegetated the barren landscape. Some hydrothermal activity remains at the lake floor, suggesting that someday in the future Mazama may erupt again. [http://craterlake.wr.usgs.gov/geology.html]

References

- Fire Mountains of the West: The Cascade and Mono Lake Volcanoes, Stephen L. Harris, (Mountain Press Publishing Company, Missoula; 1988) ISBN 0-87842-220-X
- Geology of National Parks: Fifth Edition, Ann G. Harris, Esther Tuttle, Sherwood D., Tuttle (Iowa, Kendall/Hunt Publishing; 1997) ISBN 0-7872-5353-7

External links

- [http://www.crater.lake.national-park.com/ Crater Lake National Park information]
- [http://craterlake.wr.usgs.gov/ Crater Lake Data Clearinghouse] of the United States Geological Survey
- [http://www.pbase.com/ngruev/image/36607126/large Panoramic view of Crater Lake]
- [http://www.nationalparksgallery.com/parks/Crater-Lake-National-Park Crater Lake Pictures]
- [http://www.thetownmenu.com/klamathfalls/attractions/craterlakepano.html More Crater Lake photos]
- [http://maps.google.com/maps?ll=42.942383,-122.108499&spn=0.133038,0.187798&t=k&hl=en Satellite image of Crater Lake (Google Maps)]
- [http://www.pbase.com/image/33010525 Picture and description of the Old Man of the Lake]
- [http://video.google.com/videoplay?docid=-345603526721135094 video taken from from shore of Crater Lake] Category:Volcanic calderas Category:Volcanoes of Oregon Category:Lakes of Oregon Category:Cascade Range

Sediment

Sediment is any particulate matter that can be transported by fluid flow and which eventually is deposited as a layer of solid particles on the bed or bottom of a body of water or other liquid. Sedimentation is the deposition by settling of a suspended material. Sediments are also transported by wind (eolian) and glaciers. Desert sand dunes and loess are examples of aeolian transport and deposition. Glacial moraine deposits and till are ice transported sediments. Simple gravitational collapse also creates sediments such as talus and mountainslide deposits as well as karst collapse features. Seas, oceans, and lakes accumulate sediment over time. The material can be terrigenous (originating on the land) or marine (originating in the ocean). Deposited sediments are the source of sedimentary rocks, which can contain fossils of the inhabitants of the body of water that were, upon death, covered by accumulating sediment. Lake bed sediments that have not solidified into rock can be used to determine past climatic conditions.

Sediment transport

Rivers and streams

If a fluid, such as water, is flowing, it can carry suspended particles. The settling velocity is the minimum velocity a flow must have in order to transport, rather than deposit, sediments, and (for a dilute suspension) is given by Stoke's Law: :

w=\frac

where w is the settling velocity, ρ is density (the subscripts p and f indicate particle and fluid respectively), g is the acceleration due to gravity, r is the radius of the particle and μ is the dynamic viscosity of the fluid. If the flow velocity is greater than the settling velocity, sediment will be transported downstream as suspended load. As there will always be a range of different particle sizes in the flow, some will have sufficiently large diameters that they settle on the river or stream bed, but still move downstream. This is known as bed load and the particles are transported via such mechanisms as saltation (jumping up into the flow, being transported a short distance then settling again), rolling and sliding. Saltation marks are often preserved in solid rocks and can be used to estimate the flow rate of the rivers that originally deposited the sediments.

Fluvial Bedforms

Any particle that is larger in diameter than approximately 0.7 mm will form visible topographic features on the river or stream bed. These are known as bedforms and include ripples, dunes, plane beds and antidunes. See bedforms for more detail. Again, bedforms are often preserved in sedimentary rocks and can be used to estimate the direction and magnitude of the depositing flow.

Key depositional environments

The major fluvial (river and stream) environments for deposition of sediments include: #Deltas (arguably an intermediate environment between fluvial and marine) #Point-bars #Alluvial fans #Braided rivers #Oxbow lakes #Levees

Shores and shallow seas

The second major environment where sediment may be suspended in a fluid is in seas and oceans. The sediment could consist of terrigenous material supplied by nearby rivers and streams or reworked marine sediment (e.g. sand). In the mid-ocean, living organisms are primarily responsible for the sediment accumulation, their shells sinking to the ocean floor upon death.

Marine Bedforms

Marine environments also see the formation of bedforms, whose characteristics are influenced by the tides or currents.

Key depositional environments

The major areas for deposition of sediments in the marine environment include: #Littoral sands (e.g. beach sands, coastal bars and spits, largely clastic with little faunal content) #The continental shelf (silty clays, increasing marine faunal content). #The shelf margin (low terrigenous supply, mostly calcareous faunal skeletons) #The shelf slope (much more fine-grained silts and clays) One other depositional environment which is a mixture of fluvial and marine is the turbidite system, which is a major source of sediment to the deep sedimentary and abyssal basins as well as the deep oceanic trenches.

River delta

A delta is the mouth of a river where it flows into an ocean, sea, or lake, building outwards (as a deltaic deposit) from sediment carried by the river and deposited as the water current is dissipated. Deltaic deposits of larger, heavily-laden rivers are characterised by the river channel dividing into multiple streams (distributaries), these divide and come together again to form a maze of active and inactive channels. A related notion is estuary, which is another type of the river mouth.

Delta formation

estuary, near Narsarsuaq.]] At the final course of a river, when it enters the sea, it mixes with the surrounding water, and its velocity of flow is checked, causing it to deposit its load of gravel, sand, silt and clay. The first materials deposited are the gravel and sand, as they are by far the heaviest and coarsest. Next to be dropped is the silt. Because it is fine, the clay is transported in suspension quite far out in the sea. When salt water causes the clay to flocculate, it becomes heavier and sinks. As layers upon layers of alluvial materials are deposited, a platform of alluvium is built up and it eventually rises above the water, which can now be called the delta. The water then overflows the banks into different channels called distributaries, which build up their own levees. The vegetation that later grows on the alluvium stabilizes the delta. Where delta formation is river-dominated and less subject to tidal or wave action, a delta may take on a multi-lobed shape which resembles a bird's foot. The Mississippi Delta is an example of this type. The most famous delta is that of the Nile River, and it is this delta from which the term is derived, because the Nile delta has a very characteristic triangular shape, like the (upper-case) Greek letter delta (

\Delta

). Other rivers with notable deltas include the Ganges/Brahmaputra combination (this delta spans most of Bangladesh), the Niger, the Amazon, the Mississippi, the Sacramento-San Joaquin, the Rhine, the Rhône, the Danube, the Ebro, the Volga, the Lena, the Tigris-Euphrates, the Indus, the Krishna-Godavari, the Kaveri, the Irrawaddy, and the Mekong. In rare cases the river delta is located inside of a large valley and is called an inverted river delta. Sometimes a river will divide into multiple branches in an inland area, only to rejoin and continue to the sea; such an area is known as an inland delta, and often occur on former lake beds. The Niger Inland Delta is the most famous example; another is the Danube Inland Delta on the Little Alföld. Little Alföld. These rock formations, which sometimes contain coal, cap the thick series of sedimentary rocks of the Allegheny Plateau in eastern North America, ]]

List of deltas

- Camargue (Rhône River Delta)
- Colorado River Delta
- Danube Delta
- Ganges-Brahmaputra Delta
- Indus River Delta
- Lena Delta
- Mekong Delta
- Mississippi River Delta
- Niger Inland Delta (inland delta)
- Niger River Delta (Oil Rivers)
- Nile Delta
- Okavango Delta (inland delta)
- Pearl River Delta
- Rhine-Meuse-Scheldt Delta
- Sacramento River Delta
- Volga Delta
- Yangtze River Delta
- Yukon Delta

External link

- [http://www.geol.lsu.edu/WDD/DELTA_LISTS/continents.htm Louisiana State University Geology] - World Deltas Category:Landforms Category:Ecology
- ko:삼각주 ja:三角州

Dust devil

] A dust devil or whirlwind is either a large rotating updraft, anywhere from 1000 meters high or more and tens of meters in diameter, to a small vortex a few meters high. In Australia, they are commonly known as willy willies, from an Aboriginal word.

Larger dust devils

The larger dust devils are often observed in times of atmospheric turbulence, especially common in the San Luis Valley of Colorado. Depending on the classification system used they may be considered weak tornados or landspouts. They are visible in the Great Basin and eastward to El Paso, for example. They are distinct from the common dust storms of this area, because they resemble small tornados. Due to this they are best viewed from a distance, and at a height (say, from a mountaintop). These whirlwinds are not extremely hazardous to biological organisms, but machines and electronics can suffer many severe malfunctions through repeated exposure to dust devil activity, including but not limited to increased wear from dust and short circuits or other physical damage caused by electrical arcing.

Smaller dust devils

The smaller dust devils reach only a few meters or tens of meters in height, forming commonly in hot dry weather, most observably in fields or dusty flats, where the soil makes them visible, and which may be shorter-lived.

Electrical activities

It was recently found that even small dust devils (on Earth) can produce radio noise and electrical fields greater than 10,000 volts per meter.[http://www.berkeley.edu/news/media/releases/2002/05/29_dust.html]

Martian dust devils

tornados. The long dark streak is formed by a moving swirling column of Martian atmosphere. The dust devil itself (the black spot) is climbing the crater wall. The streaks on the right are sand dunes on the crater floor.]] Dust devils also occur on Mars, and were first photographed by the Viking orbiters in the 1970s. In 1997, the Mars Pathfinder lander detected a dust devil passing over it.[http://www.ruhr-uni-bochum.de/climusa/dust.htm] Martian dust devils can be up to fifty times as wide and ten times as high as terrestrial dust devils, and large ones may pose a threat to terrestrial technology sent to Mars.[http://unisci.com/stories/20012/0606012.htm] Mission members monitoring the Spirit rover on Mars reported March 12, 2005 that a lucky encounter with a dust devil has cleaned the solar panels of that robot. Power levels have dramatically increased and daily science work is anticipated to be expanded. [http://www.space.com/missionlaunches/spirit_dust_050312.html (space.com)] A similar phenomenon (solar panels mysteriously cleaned of accumulated dust) had previously been observed with the Opportunity rover, and dust devils had also been suspected as the cause. A large-scale cyclone has also been observed on Mars.
cyclone =External links=
- [http://www.inflowimages.com/ChaseReports/DustDevils/dustdevils.asp Australian Dust Devil Photos]
- [http://www.animalu.com/pics/dd1.htm Dancing with the Devils Video]
- [http://www.nasa.gov/vision/universe/solarsystem/mer-042105.html Dust Devil Imaged by Spirit Rover on Mars]
- [http://www.retecool.com/filmpies/stormachtig.html Japanese Dust Devil Video]
- [http://www.lpl.arizona.edu/IMP/Matador/ Matador Dust Devil Project]
- [http://www.jpl.nasa.gov/news/news.cfm?release=2005-061 More pictures] of Martian dust devils from Spirit Category:Winds

2004

2004 (MMIV) was a leap year starting on Thursday of the Gregorian calendar. It was designated the:
- International Year of Rice (by the United Nations)
- International Year to Commemorate the Struggle against Slavery and its Abolition (by UNESCO)
- 2004 World Health Day topic was Road Safety (by World Health Organization)
- Year of the Monkey (by the Chinese calendar) See the world in 2004 for a description of the state of the world in this year. See also Wikipedia's almanac of events for this year.
Events

January

- January 1 - Pervez Musharraf gets a vote of confidence from an electoral college consisting of Parliament and the provincial assemblies, confirming him as President of Pakistan until 2007.
- January 3 - Flash Airlines Flight 604 crashes into the Red Sea off the coast of Egypt, killing all 148 aboard.
- January 4 - Mikhail Saakashvili wins the presidential elections in Georgia.
- January 4 -NASA's MER-A (Spirit) lands on Mars.
- January 8 - Queen Elizabeth II christens the RMS Queen Mary 2 cruise liner, currently the largest ocean liner in the world.
- January 13 - An Uzbekistan Airways plane crashes in Uzbekistan's capital of Tashkent, killing 37.
- January 22 - The European Union bans the import of poultry from Thailand, as bird flu spreads throughout Southeast Asia.
- January 24 - NASA's MER-B (Opportunity) lands on Mars.
- January 27 - The British government narrowly wins a House of Commons vote on the proposed introduction of tuition top-up fees in British universities.
- January 28 - The findings of the Hutton Inquiry are published in London. The British Government is found not to have falsified information in the "sexed up dossier". The report criticises the BBC's role in the death of David Kelly, a weapons expert on Iraq.
- January 28 - At a hearing of the National Commission on Terrorist Attacks Upon the United States, it is revealed that the September 11, 2001, terrorists used Mace (a brand of tear gas) or pepper spray in overpowering the flight crew of American Airlines Flight 11.
February

- February 1 - A hajj stampede in Mina, Saudi Arabia, kills 251 pilgrims.
- February 3 - The CIA admits that there was no imminent threat from weapons of mass destruction before the 2003 invasion of Iraq.
- February 6 - A suicide bomber kills 41 people on a metro car in Moscow.
- February 7 - Several leaders of Abnaa el-Balad arrested in Israel.
- February 10 - At least 50 people killed in a car bomb attack on a police recruitment centre south of Baghdad.
- February 10 - The French National Assembly votes to pass a law banning religious items and clothing from schools.
- February 12 - Same sex marriage in the United States: The City and County of San Francisco begins issuing marriage licenses to same-sex couples as an act of civil disobedience.
- February 13 - Scientists in South Korea announce the cloning of 30 human embryos.
- February 14 - Riots break out between New South Wales Police and Aboriginal residents of Redfern, a suburb of Sydney, Australia.
- February 18 - A train carrying a convoy of petrol, fertiliser, and sulfur derails and explodes in Iran, killing 320 people.
- February 20 - Conservatives win a majority in the Iranian parliament election.
- February 24 - 6.5 Richter scale earthquake in Northern Morocco hits in the Rif mountains near the city of Al Hoceima - over 400 dead. Ait Kamara is destroyed. 517 dead.
- February 25- Ash Wednesday. Also, the religious docudrama, The Passion of the Christ was released.
- February 26 - The United States lifts a ban on travel to Libya, ending travel restrictions to the nation that had lasted for 23 years.
- February 26 - Macedonian President Boris Trajkovski is killed in a plane crash near Mostar, Bosnia and Herzegovina.
- February 29 - 2004 Haiti rebellion: Jean-Bertrand Aristide resigns as president of Haiti. The chief justice of the Haitian Supreme Court, Boniface Alexandre, is sworn in as interim president.
- February 29 - The film The Lord of the Rings: The Return of the King directed by Peter Jackson wins 11 Academy Awards in every category it was nominated.
March

- March 2 - John Kerry effectively clinches the 2004 U.S. Democratic Party presidential nomination by winning nine out of 10 "Super Tuesday" primaries and caucuses.
- March 2 - NASA announces that the Mars rover MER-B (Opportunity), has confirmed that the area of Mars they landed in was once drenched in water.
- March 10 - Five British men released from detention at Camp Delta, Guantanamo Bay land at RAF Brize Norton. Four are immediately arrested for questioning.
- March 11 - Simultaneous explosions on rush hour trains in Madrid kill 190 people.
- March 12 - Following the terrorist attacks in Madrid on March 11, millions of protesters take to the streets of Spanish cities against terrorism.
- March 14 - Two suicide bombers kill eleven Israeli civilians in Ashdod, Israel.
- March 14 - The Spanish parliamentary elections of 2004 take place. The incumbent government led by José María Aznar is defeated by the Socialist José Luis Rodríguez Zapatero.
- March 14 - Presidential elections in Russia are held. Vladimir Putin easily wins a second term.
- March 15 - A trio of astronomers announce they have discovered a large trans-Neptunian object, the largest object found in the solar system since Pluto was discovered in 1930. Initially designated 2003 VB₁₂, it was named 90377 Sedna in late September.
- March 15 - The new Spanish government announces that it will withdraw Spain's 1,300 troops in Iraq.
- March 17 - Organized violence breaks out over two days in Kosovo. Nineteen people are killed, 139 Serbian homes are burned, schools and businesses are vandalized, and over 30 orthodox monasteries and churches are burned and destroyed.
- March 19 - The UN launches a corruption investigation due to the scandal over its Iraqi Oil for Food program.
- March 20 - President Chen Shui-bian wins the Taiwanese presidential election by 0.2% of the vote. The day before, he and Vice President Annette Lu were 'shot'. Lien Chan refuses to concede and demands a recount. A controversial 'peace referendum' opposed by the People's Republic of China is invalidated.
- March 21 - The 2004 Malaysian general election takes place. The incumbent Barisan Nasional party wins 198 out of 219 seats in the Malaysian Parliament.
- March 21 - Tony Saca is elected President of El Salvador (inauguration June 1).
- March 22 - Palestinians protest in the streets after an Israeli helicopter gunship fires a missile at the entourage of Ahmed Yassin in Gaza City, killing Yassin and 7 others.
- March 25 - British Prime Minister Tony Blair visits Libyan leader Colonel Muammar al-Qaddafi, in return for the dismantling of Libya's WMD programme in December 2003 - the first time a major western leader has visited the nation in several decades.
- March 28 - In France, the government of Prime Minister Jean-Pierre Raffarin suffers a stunning and unprecedented defeat in regional elections. The first ever South Atlantic Hurricane makes landfall in South Brazil on the state of Santa Catarina, the Hurricane is dubbed Hurricane Catarina.
- March 29 - The Republic of Ireland bans smoking in all enclosed work places including: restaurants, pubs and bars.
- March 29 - Largest expansion of NATO to date, allowing Bulgaria, Estonia, Latvia, Lithuania, Romania, Slovakia and Slovenia into the organization.
- March 31 - Four American private military contractors working for Blackwater USA, are killed and their bodies mutilated after being ambushed in Fallujah, Iraq.
April

- April 1 - Faroese Prime Minister's Office announces that from then on the Prime Minister and the Prime Minister's Office would use a new version of the Faroese Coat of Arms. The colours were inspired from the Merkið (flag) and yellow/gold was added. The new Coat of Arms depicts a Ram on a blue shield ready to defend. It can be used by the Government Ministries and by Faroese embassies, but some still use older versions of the Coat of Arms. Coat of Arms
- April 3 - A bomb explosion in a Madrid flat kills a Spanish policeman and five terrorists suspected of responsibility for the Madrid train bombings on March 11.
- April 4 - Serious fighting breaks out in Najaf, Sadr City, and Basra in Iraq as Shia