by neufer » Wed May 12, 2021 2:53 pm
https://en.wikipedia.org/wiki/Mojave_(crater) wrote:
Click to play embedded YouTube video.
<<Mojave is a 58 km diameter impact crater in the Oxia Palus quadrangle of Mars. The crater is located at 7.5° N and 33.0° W within the Martian Xanthe Terra region. Some parts of the crater display a high concentration of closely spaced pits. Pits show little or no evidence of rims or ejecta. The pits are so close to each other that adjacent pits often share the same wall. It is believed that the pits form from steam produced when the heat from the impact process interacts with ice in the ground.
Mojave is a rayed crater, another indication of its youth, and is the largest such crater on Mars. Based on crater counts of its ejecta blanket, it is thought to be about 3 million years old. It is believed to be the most recent crater of its size on Mars, and has been identified as the probable source of the shergottite meteorites collected on Earth.
The depth of Mojave is approximately 2,600 meters. Based on its ratio of depth to diameter, researchers believe it is very young. It is not old enough to have accumulated much material and start to fill. Its relatively undegraded state helps scientists model impact processes on Mars. If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.>>
https://en.wikipedia.org/wiki/Asteroid_belt wrote:
Click to play embedded YouTube video.
<<The high population of the asteroid belt makes for a very active environment, where collisions between asteroids occur frequently (on astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years. A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family).
Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Due to the Poynting–Robertson effect, the pressure of solar radiation causes this dust to slowly spiral inward toward the Sun.
The combination of this fine asteroid dust, as well as ejected cometary material, produces the zodiacal light. Asteroid particles that produce the visible zodiacal light average about 40 μm in radius.
The typical lifetimes of main-belt zodiacal cloud particles are about 700,000 years. Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid belt. It was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 percent of the zodiacal-light dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At most 10 percent of the dust is attributed to the asteroid belt.>>
https://en.wikipedia.org/wiki/Martian_meteorite#Shergottites wrote:
<<Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are named after the Shergotty meteorite, which fell at Sherghati, India in 1865. Shergottites are igneous rocks of mafic to ultramafic lithology. They fall into three main groups, the basaltic, olivine-phyric (such as the
Tissint group found in Morocco in 2011) and Lherzolitic shergottites, based on their crystal size and mineral content. They can be categorised alternatively into three or four groups based on their rare-earth element content. These two classification systems do not line up with each other, hinting at complex relationships between the various source rocks and magmas from which the shergottites formed.>>
https://en.wikipedia.org/wiki/Tissint_meteorite wrote:
<<On July 18, 2011, around 2 AM local time, a bright fireball was observed by several people in the Oued Drâa valley, east of Tata, Morocco. One observer reported that the fireball was initially yellow in color, then turned green, illuminating the entire area before it appeared to break into two pieces; two sonic booms were heard over the valley. In October 2011, nomads began to find very fresh, fusion-crusted stones in a remote area of the Oued Drâa intermittent watershed. The Tissint meteorite was named after the town of Tissint, 48 kilometres away from the fall site. Dozens of fragments with masses ranging from 0.2 to 1,282 grams were collected, totaling roughly 12–15 kilograms.
The meteorite was ejected from the surface of Mars between 700,000 and 1.1 million years ago. Tissint appears to be derived from a deep mantle source region that was unlike any of the other known Martian shergottite meteorites. The material is highly shocked and indicates it was ejected during the largest impact excavation in record. Given the widely dispersed shock melting observed in
Tissint, alteration of other soft minerals (carbonates, halides, sulfates and even organics), especially along grain boundaries, might have occurred. This may in part explain the lack of such minerals in
Tissint, but it is unknown if it is of biotic origin.
The meteorite fragments were recovered within days after the fall, so it is considered an "uncontaminated" meteorite. The meteorite displays evidence of water weathering, and there are signs of elements being carried into cracks in the rocks by water or fluid, which is something never seen before in a Martian meteorite. Specifically, scientists found carbon and nitrogen-containing compounds associated with hydrothermal mineral inclusions. One team reported measuring an elevated carbon-13 ratio, while another team reported a low
13C ratio as compared to the content in Mars' atmosphere and crust, and suggested that it may be of biological origin, but the researchers also noted that there are several geological processes that could explain that without invoking complex life-processes; for example, it could be of meteoritic origin and would have been mixed with Martian soil when meteorites and comets impact the surface of Mars, or of volcanic origin.
The data on refractory trace elements, sulfur and fluorine as well as the data on the isotopic composition of nitrogen, argon and carbon released upon heating from the matrix and glass veins in the meteorite unambiguously indicate the presence of a Martian surface component including trapped atmospheric gases. So, the influence of in situ Martian weathering can be distinguished from terrestrial contamination in the meteorite. The Martian weathering features in Tissint are compatible with the results of spacecraft observations of Mars, and
Tissint has a cosmic ray dating exposure age of 0.7 ± 0.3 Ma—consistent with the reading of many other shergottites, notably EETA79001, suggesting that they were ejected from Mars during the same event.
The overall composition of the Tissint meteorite corresponds to that of aluminium-poor ferroan basaltic rock, which likely originated as a result of magmatic activity at the surface of Mars. These basalt then underwent weathering by fluids, which deposited minerals enriched in incompatible elements in fissures and cracks. A later impact on the surface of Mars melted the leached material forming black glassy veins.
Finally shergottites were ejected from Mars about 0.7 million years ago.>>
[quote=https://en.wikipedia.org/wiki/Mojave_(crater)]
[float=left][youtube]https://www.youtube.com/watch?v=k7ji4wM74wo[/youtube][img3=Mojave Crater: 7.5°N 33.0°W / Mars Pathfinder: 19.13°N 33.22°W]https://upload.wikimedia.org/wikipedia/commons/0/0a/USGS-Mars-MC-11-OxiaPalusRegion-mola.png[/img3][/float]
<<Mojave is a 58 km diameter impact crater in the Oxia Palus quadrangle of Mars. The crater is located at 7.5° N and 33.0° W within the Martian Xanthe Terra region. Some parts of the crater display a high concentration of closely spaced pits. Pits show little or no evidence of rims or ejecta. The pits are so close to each other that adjacent pits often share the same wall. It is believed that the pits form from steam produced when the heat from the impact process interacts with ice in the ground. [b][u][color=#0000FF]Mojave is a rayed crater, another indication of its youth, and is the largest such crater on Mars. Based on crater counts of its ejecta blanket, it is thought to be about 3 million years old. It is believed to be the most recent crater of its size on Mars, and has been identified as the probable source of the shergottite meteorites collected on Earth.[/color][/u][/b]
The depth of Mojave is approximately 2,600 meters. Based on its ratio of depth to diameter, researchers believe it is very young. It is not old enough to have accumulated much material and start to fill. Its relatively undegraded state helps scientists model impact processes on Mars. If one measures the diameter of a crater, the original depth can be estimated with various ratios. Because of this relationship, researchers have found that many Martian craters contain a great deal of material; much of it is believed to be ice deposited when the climate was different.>>[/quote][quote=https://en.wikipedia.org/wiki/Asteroid_belt]
[float=right][youtube]https://www.youtube.com/watch?v=ve0jLXEzFXE[/youtube][/float]
<<The high population of the asteroid belt makes for a very active environment, where collisions between asteroids occur frequently (on astronomical time scales). Collisions between main-belt bodies with a mean radius of 10 km are expected to occur about once every 10 million years. A collision may fragment an asteroid into numerous smaller pieces (leading to the formation of a new asteroid family).
Along with the asteroid bodies, the asteroid belt also contains bands of dust with particle radii of up to a few hundred micrometres. This fine material is produced, at least in part, from collisions between asteroids, and by the impact of micrometeorites upon the asteroids. Due to the Poynting–Robertson effect, the pressure of solar radiation causes this dust to slowly spiral inward toward the Sun.
The combination of this fine asteroid dust, as well as ejected cometary material, produces the zodiacal light. Asteroid particles that produce the visible zodiacal light average about 40 μm in radius. [size=125][b][u][color=#0000FF]The typical lifetimes of main-belt zodiacal cloud particles are about 700,000 years.[/color][/u][/b][/size] Thus, to maintain the bands of dust, new particles must be steadily produced within the asteroid belt. It was once thought that collisions of asteroids form a major component of the zodiacal light. However, computer simulations by Nesvorný and colleagues attributed 85 percent of the zodiacal-light dust to fragmentations of Jupiter-family comets, rather than to comets and collisions between asteroids in the asteroid belt. At most 10 percent of the dust is attributed to the asteroid belt.>>[/quote][quote=https://en.wikipedia.org/wiki/Martian_meteorite#Shergottites]
[float=left][img3=NWA 6963, a shergottite found in Morocco, September 2011.]https://upload.wikimedia.org/wikipedia/commons/thumb/c/cf/NWA_6963_full_slice.jpg/330px-NWA_6963_full_slice.jpg[/img3][/float]
<<Roughly three-quarters of all Martian meteorites can be classified as shergottites. They are named after the Shergotty meteorite, which fell at Sherghati, India in 1865. Shergottites are igneous rocks of mafic to ultramafic lithology. They fall into three main groups, the basaltic, olivine-phyric (such as the [b][u][color=#FF0000]Tissint[/color][/u][/b] group found in Morocco in 2011) and Lherzolitic shergottites, based on their crystal size and mineral content. They can be categorised alternatively into three or four groups based on their rare-earth element content. These two classification systems do not line up with each other, hinting at complex relationships between the various source rocks and magmas from which the shergottites formed.>>[/quote][quote=https://en.wikipedia.org/wiki/Tissint_meteorite]
[float=left][img3=Piece of the Tissint meteorite with glossy black fusion crust & light gray matrix]https://upload.wikimedia.org/wikipedia/commons/thumb/5/5b/Tissint_meteorite.jpg/398px-Tissint_meteorite.jpg[/img3][img3=Number of asteroids in the asteroid belt as a function of their semi-major axis. The dashed lines indicate the Kirkwood gaps, where orbital resonances with Jupiter destabilize orbits. The color gives a possible division into three zones]https://upload.wikimedia.org/wikipedia/commons/d/d3/Kirkwood_Gaps.svg[/img3][/float]
<<On July 18, 2011, around 2 AM local time, a bright fireball was observed by several people in the Oued Drâa valley, east of Tata, Morocco. One observer reported that the fireball was initially yellow in color, then turned green, illuminating the entire area before it appeared to break into two pieces; two sonic booms were heard over the valley. In October 2011, nomads began to find very fresh, fusion-crusted stones in a remote area of the Oued Drâa intermittent watershed. The Tissint meteorite was named after the town of Tissint, 48 kilometres away from the fall site. Dozens of fragments with masses ranging from 0.2 to 1,282 grams were collected, totaling roughly 12–15 kilograms.
[size=125][b][u][color=#0000FF]The meteorite was ejected from the surface of Mars between 700,000 and 1.1 million years ago[/color][/u][/b]. [/size]Tissint appears to be derived from a deep mantle source region that was unlike any of the other known Martian shergottite meteorites. The material is highly shocked and indicates it was ejected during the largest impact excavation in record. Given the widely dispersed shock melting observed in [b][u][color=#FF0000]Tissint[/color][/u][/b], alteration of other soft minerals (carbonates, halides, sulfates and even organics), especially along grain boundaries, might have occurred. This may in part explain the lack of such minerals in [b][u][color=#FF0000]Tissint[/color][/u][/b], but it is unknown if it is of biotic origin.
The meteorite fragments were recovered within days after the fall, so it is considered an "uncontaminated" meteorite. The meteorite displays evidence of water weathering, and there are signs of elements being carried into cracks in the rocks by water or fluid, which is something never seen before in a Martian meteorite. Specifically, scientists found carbon and nitrogen-containing compounds associated with hydrothermal mineral inclusions. One team reported measuring an elevated carbon-13 ratio, while another team reported a low [sup]13[/sup]C ratio as compared to the content in Mars' atmosphere and crust, and suggested that it may be of biological origin, but the researchers also noted that there are several geological processes that could explain that without invoking complex life-processes; for example, it could be of meteoritic origin and would have been mixed with Martian soil when meteorites and comets impact the surface of Mars, or of volcanic origin.
The data on refractory trace elements, sulfur and fluorine as well as the data on the isotopic composition of nitrogen, argon and carbon released upon heating from the matrix and glass veins in the meteorite unambiguously indicate the presence of a Martian surface component including trapped atmospheric gases. So, the influence of in situ Martian weathering can be distinguished from terrestrial contamination in the meteorite. The Martian weathering features in Tissint are compatible with the results of spacecraft observations of Mars, and [b][u][color=#0000FF]Tissint has a cosmic ray dating exposure age of 0.7 ± 0.3 Ma—consistent with the reading of many other shergottites, notably EETA79001, suggesting that they were ejected from Mars during the same event.[/color][/u][/b]
The overall composition of the Tissint meteorite corresponds to that of aluminium-poor ferroan basaltic rock, which likely originated as a result of magmatic activity at the surface of Mars. These basalt then underwent weathering by fluids, which deposited minerals enriched in incompatible elements in fissures and cracks. A later impact on the surface of Mars melted the leached material forming black glassy veins. [size=125][b][u][color=#0000FF]Finally shergottites were ejected from Mars about 0.7 million years ago.[/color][/u][/b][/size]>>[/quote]