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Noachian Period
The Noachian is a geologic system and early time period on the planet Mars characterized by high rates of meteorite and asteroid impacts and the possible presence of abundant surface water. The absolute age of the Noachian period is uncertain but probably corresponds to the lunar Pre-Nectarian to Early Imbrian periods of 4100 to 3700 million years ago, during the interval known as the Late Heavy Bombardment. Many of the large impact basins on the Moon and Mars formed at this time. The Noachian Period is roughly equivalent to the Earth's Hadean and early Archean eons when the first life forms likely arose. Noachian-aged terrains on Mars are prime spacecraft landing sites to search for fossil evidence of life. During the Noachian, the atmosphere of Mars was denser than it is today, and the climate possibly warm enough to allow rainfall. Large lakes and rivers were present in the southern hemisphere, and an ocean may have covered the low-lying northern plains. Extensive volcanism o ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Mars Orbital Laser Altimeter
260px, MOLA topographic images of the two hemispheres of Mars. This image appeared on the cover of ''Science'' magazine in May 1999. The Mars Orbiter Laser Altimeter (MOLA) was one of five instruments on the ''Mars Global Surveyor'' (MGS) spacecraft, which operated in Mars orbit from September 1997 to November 2006. However, the MOLA instrument transmitted altimetry data only until June 2001. The MOLA instrument transmitted infrared laser pulses towards Mars at a rate of 10 times per second, and measured the time of flight to determine the range (distance) of the MGS spacecraft to the Martian surface. The range measurements resulted in precise topographic maps of Mars. The precision maps are applicable to studies in geophysics, geology and atmospheric circulation. MOLA also functioned as a passive radiometer, and measured the radiance of the surface of Mars at 1064 nanometers. Planetary laser altimetry A laser altimeter is an instrument that measures the distance from an orbiti ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Late Heavy Bombardment
The Late Heavy Bombardment (LHB), or lunar cataclysm, is a hypothesized event thought to have occurred approximately 4.1 to 3.8 billion years (Ga) ago, at a time corresponding to the Neohadean and Eoarchean eras on Earth. According to the hypothesis, during this interval, a disproportionately large number of asteroids and comets collided with the early terrestrial planets in the inner Solar System, including Mercury, Venus, Earth and Mars. These came from both post-accretion and planetary instability-driven populations of impactors. Although widely accepted, it remains difficult to prove conclusively. Evidence for the LHB derives from rock samples of Moon craters brought back by the Apollo astronauts. Isotopic dating showed that the rocks were last molten during impact events in a rather narrow interval of time, suggesting that a large proportion of craters were formed during this period. Several hypotheses attempt to explain this apparent spike in the flux of impactors in ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Phyllosilicates
Silicate minerals are rock-forming minerals made up of silicate groups. They are the largest and most important class of minerals and make up approximately 90 percent of Earth's crust. In mineralogy, silica (silicon dioxide, ) is usually considered a silicate mineral. Silica is found in nature as the mineral quartz, and its polymorphs. On Earth, a wide variety of silicate minerals occur in an even wider range of combinations as a result of the processes that have been forming and re-working the crust for billions of years. These processes include partial melting, crystallization, fractionation, metamorphism, weathering, and diagenesis. Living organisms also contribute to this geologic cycle. For example, a type of plankton known as diatoms construct their exoskeletons ("frustules") from silica extracted from seawater. The frustules of dead diatoms are a major constituent of deep ocean sediment, and of diatomaceous earth. General structure A silicate mineral is generally an ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Clay Minerals
Clay minerals are hydrous aluminium phyllosilicates (e.g. kaolin, Al2 Si2 O5( OH)4), sometimes with variable amounts of iron, magnesium, alkali metals, alkaline earths, and other cations found on or near some planetary surfaces. Clay minerals form in the presence of water and have been important to life, and many theories of abiogenesis involve them. They are important constituents of soils, and have been useful to humans since ancient times in agriculture and manufacturing. Properties Clay is a very fine-grained geologic material that develops plasticity when wet, but becomes hard, brittle and non–plastic upon drying or firing. It is a very common material, and is the oldest known ceramic. Prehistoric humans discovered the useful properties of clay and used it for making pottery. The chemistry of clay, including its capacity to retain nutrient cations such as potassium and ammonium, is important to soil fertility. Because the individual particles in clay are less tha ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Weathering
Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs ''in situ'' (on site, with little or no movement), and so is distinct from erosion, which involves the transport of rocks and minerals by agents such as water, ice, snow, wind, waves and gravity. Weathering processes are divided into ''physical'' and ''chemical weathering''. Physical weathering involves the breakdown of rocks and soils through the mechanical effects of heat, water, ice, or other agents. Chemical weathering involves the chemical reaction of water, atmospheric gases, and biologically produced chemicals with rocks and soils. Water is the principal agent behind both physical and chemical weathering, though atmospheric oxygen and carbon dioxide and the activities of biological organisms are also important. Chemical weathering by biological action is also known as biological wea ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tharsis Bulge
Tharsis () is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as the Tharsis Montes. The tallest volcano on the planet, Olympus Mons, is often associated with the Tharsis region but is actually located off the western edge of the plateau. The name Tharsis is the Greco-Latin transliteration of the biblical Tarshish, the land at the western extremity of the known world. Location and size Tharsis can have many meanings depending on historical and scientific context. The name is commonly used in a broad sense to represent a continent-sized region of anomalously elevated terrain centered just south of the equator around longitude 265°E.Carr, M.H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, p. 46. . Called the Tharsis bulge or Th ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Tharsis
Tharsis () is a vast volcanic plateau centered near the equator in the western hemisphere of Mars. The region is home to the largest volcanoes in the Solar System, including the three enormous shield volcanoes Arsia Mons, Pavonis Mons, and Ascraeus Mons, which are collectively known as the Tharsis Montes. The tallest volcano on the planet, Olympus Mons, is often associated with the Tharsis region but is actually located off the western edge of the plateau. The name Tharsis is the Greco-Latin transliteration of the biblical Tarshish, the land at the western extremity of the known world. Location and size Tharsis can have many meanings depending on historical and scientific context. The name is commonly used in a broad sense to represent a continent-sized region of anomalously elevated terrain centered just south of the equator around longitude 265°E.Carr, M.H. (2006). ''The Surface of Mars;'' Cambridge University Press: Cambridge, UK, p. 46. . Called the Tharsis bulge or Thar ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Volcanism
Volcanism, vulcanism or volcanicity is the phenomenon of eruption of molten rock (magma) onto the surface of the Earth or a solid-surface planet or moon, where lava, pyroclastics, and volcanic gases erupt through a break in the surface called a vent. It includes all phenomena resulting from and causing magma within the crust or mantle of the body, to rise through the crust and form volcanic rocks on the surface. Magmas, that reach the surface and solidify, form extrusive landforms. Volcanic processes Magma from the mantle or lower crust rises through the crust towards the surface. If magma reaches the surface, its behavior depends on the viscosity of the molten constituent rock. Viscous (thick) magma produces volcanoes characterised by explosive eruptions, while non-viscous (runny) magma produce volcanoes characterised by effusive eruptions pouring large amounts of lava onto the surface. In some cases, rising magma can cool and solidify without reaching the surface. Inste ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Atmosphere
An atmosphere () is a layer of gas or layers of gases that envelop a planet, and is held in place by the gravity of the planetary body. A planet retains an atmosphere when the gravity is great and the temperature of the atmosphere is low. A stellar atmosphere is the outer region of a star, which includes the layers above the opaque photosphere; stars of low temperature might have outer atmospheres containing compound molecules. The atmosphere of Earth is composed of nitrogen (78%), oxygen (21%), argon (0.9%), carbon dioxide (0.04%) and trace gases. Most organisms use oxygen for respiration; lightning and bacteria perform nitrogen fixation to produce ammonia that is used to make nucleotides and amino acids; plants, algae, and cyanobacteria use carbon dioxide for photosynthesis. The layered composition of the atmosphere minimises the harmful effects of sunlight, ultraviolet radiation, the solar wind, and cosmic rays to protect organisms from genetic damage. The current comp ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Extraterrestrial Life
Extraterrestrial life, colloquially referred to as alien life, is life that may occur outside Earth and which did not originate on Earth. No extraterrestrial life has yet been conclusively detected, although efforts are underway. Such life might range from simple forms like prokaryotes to intelligent beings, possibly bringing forth civilizations that might be far more advanced than humankind. The Drake equation speculates about the existence of sapient life elsewhere in the universe. The science of extraterrestrial life is known as astrobiology. Speculation about the possibility of inhabited "worlds" outside the planet Earth dates back to antiquity. Multiple early Christian writers discussed the idea of a "plurality of worlds" as proposed by earlier thinkers such as Democritus; Augustine references Epicurus's idea of innumerable worlds "throughout the boundless immensity of space" (originally expressed in his Letter to Herodotus) in ''The City of God''. In his first century p ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved in amber, hair, petrified wood and DNA remnants. The totality of fossils is known as the ''fossil record''. Paleontology is the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years old to 4.1 billion years old. Early edition, published online before print. The observation in the 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
Lander (spacecraft)
A lander is a spacecraft that descends towards, comes to rest on, the surface of an astronomical body. In contrast to an impact probe, which makes a hard landing that damages or destroys the probe upon reaching the surface, a lander makes a soft landing after which the probe remains functional. For bodies with atmospheres, the landing occurs after atmospheric entry. In these cases, landers may employ parachutes to slow them down enough to maintain a low terminal velocity. In some cases, small landing rockets will be fired just before impact in order to reduce the lander's velocity. Landing may be accomplished by controlled descent and set down on landing gear, with the possible addition of a post-landing attachment mechanism (such as the mechanism used by ''Philae'') for celestial bodies with low gravity. Some missions (for example, Luna 9 and Mars Pathfinder) used inflatable airbags to cushion the lander's impact rather than utilizing more traditional landing gear. When a hi ... [...More Info...] [...Related Items...] OR: [Wikipedia] [Google] [Baidu] |
