Skip to main content

Sumarian salt burn

 


From Wikipedia, the free encyclopedia
  (Redirected from Lunar science)
Jump to navigationJump to search

Topography of the Moon measured from the Lunar Orbiter Laser Altimeter on the mission Lunar Reconnaissance Orbiter, referenced to a sphere of radius 1737.4 km
Topography of the Moon.
STL 3D model of the Moon with 10× elevation exaggeration rendered with data from the Lunar Orbiter Laser Altimeter of the Lunar Reconnaissance Orbiter

The topography of the Moon (also known as geography of the Mooncartography of the Moonselenography, or selenodesy[1]) is the mapping of the Moon's surface and the study of its shape. It has been measured by the methods of laser altimetry and stereo image analysis, including data obtained during several missions. The most visible topographical feature is the giant far side South Pole-Aitken basin, which possesses the lowest elevations of the Moon. The highest elevations are found just to the northeast of this basin, and it has been suggested that this area might represent thick ejecta deposits that were emplaced during an oblique South Pole-Aitken basin impact event. Other large impact basins, such as the maria ImbriumSerenitatisCrisiumSmythii, and Orientale, also possess regionally low elevations and elevated rims.

Another distinguishing feature of the Moon's shape is that the elevations are on average about 1.9 km higher on the far side than the near side. If it is assumed that the crust is in isostatic equilibrium, and that the density of the crust is everywhere the same, then the higher elevations would be associated with a thicker crust. Using gravity, topography and seismic data, the crust is thought to be on average about 50 ± 15 km thick, with the far-side crust being on average thicker than the near side by about 15 km.[2][obsolete source]

Moons of Saturn

From Wikipedia, the free encyclopedia
Jump to navigationJump to search
Artist's concepts of the Saturnian ring–moon system
A spherical yellow-brownish body (Saturn) can be seen on the left. It is viewed at an oblique angle with respect to its equatorial plane. Around Saturn there are rings and small ring moons. Further to the right large round moons are shown in order of their distance.
Saturn, its rings and major icy moons—from Mimas to Rhea
In the foreground there are six round fully illuminated bodies and some small irregular objects. A large half-illuminated body is shown in the background with circular cloud bands around the partially darkened north pole visible.
Images of several moons of Saturn. From left to right: Mimas, Enceladus, Tethys, Dione, Rhea; Titan in the background; Iapetus (top right) and irregularly shaped Hyperion (bottom right). Some small moons are also shown. All to scale.

The moons of Saturn are numerous and diverse, ranging from tiny moonlets only tens of meters across to enormous Titan, which is larger than the planet MercurySaturn has 83 moons with confirmed orbits that are not embedded in its rings[1]—of which only 13 have diameters greater than 50 kilometers—as well as dense rings that contain millions of embedded moonlets and innumerable smaller ring particles.[2][3][4] Seven Saturnian moons are large enough to have collapsed into a relaxed, ellipsoidal shape, though only one or two of those, Titan and possibly Rhea, are currently in hydrostatic equilibrium. Particularly notable among Saturn's moons are Titan, the second-largest moon in the Solar System (after Jupiter's Ganymede), with a nitrogen-rich Earth-like atmosphere and a landscape featuring dry river networks and hydrocarbon lakes,[5] Enceladus, which emits jets of gas and dust from its south-polar region,[6] and Iapetus, with its contrasting black and white hemispheres.

Twenty-four of Saturn's moons are regular satellites; they have prograde orbits not greatly inclined to Saturn's equatorial plane.[7] They include the seven major satellites, four small moons that exist in a trojan orbit with larger moons, two mutually co-orbital moons and two moons that act as shepherds of Saturn's F Ring. Two other known regular satellites orbit within gaps in Saturn's rings. The relatively large Hyperion is locked in a resonance with Titan. The remaining regular moons orbit near the outer edge of the A Ring, within the G Ring and between the major moons Mimas and Enceladus. The regular satellites are traditionally named after Titans and Titanesses or other figures associated with the mythological Saturn.

The remaining fifty-nine, with mean diameters ranging from 4 to 213 km, are irregular satellites, whose orbits are much farther from Saturn, have high inclinations, and are mixed between prograde and retrograde. These moons are probably captured minor planets, or debris from the breakup of such bodies after they were captured, creating collisional families. The irregular satellites have been classified by their orbital characteristics into the InuitNorse, and Gallic groups, and their names are chosen from the corresponding mythologies, with two exceptions. One of these is Phoebe (part of the Norse group but named for a Greek Titaness), the ninth moon of Saturn and largest irregular, discovered at the end of the 19th century; the other is Bebhionn, which, though in the Gallic group, is named after an Irish goddess.

The rings of Saturn are made up of objects ranging in size from microscopic to moonlets hundreds of meters across, each in its own orbit around Saturn.[8] Thus a precise number of Saturnian moons cannot be given, because there is no objective boundary between the countless small anonymous objects that form Saturn's ring system and the larger objects that have been named as moons. Over 150 moonlets embedded in the rings have been detected by the disturbance they create in the surrounding ring material, though this is thought to be only a small sample of the total population of such objects.[9]

There are still 30 unnamed moons (as of November 2021), of which all but one is irregular. If named, they will receive names from Gallic, Norse and Inuit mythology based on the orbital groups of the moons.[10][11]Selenography[edit source]

Topography[edit source]

High resolution topographic map of Mars based on the Mars Global Surveyor laser altimeter research led by Maria Zuber and David Smith. North is at the top. Notable features include the Tharsis volcanoes in the west (including Olympus Mons), Valles Marineris to the east of Tharsis, and Hellas basin in the southern hemisphere.
STL 3D model of Mars with 20× elevation exaggeration using data from the Mars Global Surveyor Mars Orbiter Laser Altimeter.
Mars, 2001, with the southern polar ice cap visible on the bottom.
North Polar region with icecap.

Across a whole planet, generalisation is not possible, and the geography of Mars varies considerably. However, 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 ErythraeumMare Sirenum and Aurorae Sinus. The largest dark feature seen from Earth is Syrtis Major Planum.

The shield volcanoOlympus Mons (Mount Olympus), rises 22 km above the surrounding volcanic plains, and is the highest known mountain on any planet in the solar system.[8] It is in a vast upland region called Tharsis, which contains several large volcanos. See list of mountains on Mars. The Tharsis region of Mars also has the solar system's largest canyon system, Valles Marineris or the Mariner Valley, which is 4,000 km long and 7 km deep. Mars is also scarred by countless impact craters. The largest of these is the Hellas impact basin. See list of craters on Mars.

Mars has two permanent polar ice caps, the northern one located at Planum Boreum and the southern one at Planum Australe.

The difference between Mars's highest and lowest points is nearly 30 km (from the top of Olympus Mons at an altitude of 21.2 km to the bottom of the Hellas impact basin at an altitude of 8.2 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.

Martian dichotomy[edit source]

Observers of Martian topography will notice a dichotomy between the northern and southern hemispheres. Most of the northern hemisphere is flat, with few impact craters, and lies below the conventional 'zero elevation' level. In contrast, the southern hemisphere is mountains and highlands, mostly well above zero elevation. The two hemispheres differ in elevation by 1 to 3 km. The border separating the two areas is very interesting to geologists.

One distinctive feature is the fretted terrain.[14] It contains mesas, knobs, and flat-floored valleys having walls about a mile high. Around many of the mesas and knobs are lobate debris aprons that have been shown to be rock-covered glaciers.[15]

Other interesting features are the large river valleys and outflow channels that cut through the dichotomy.[16][17][18]

The northern lowlands comprise about one-third of the surface of Mars and are relatively flat, with occasional impact craters. The other two-thirds of the Martian surface are the southern highlands. The difference in elevation between the hemispheres is dramatic. Because of the density of impact craters, scientists believe the southern hemisphere to be far older than the northern plains.[19] Much of heavily cratered southern highlands date back to the period of heavy bombardment, the Noachian.

Multiple hypotheses have been proposed to explain the differences. The three most commonly accepted are a single mega-impact, multiple impacts, and endogenic processes such as mantle convection.[16] Both impact-related hypotheses involve processes that could have occurred before the end of the primordial bombardment, implying that the crustal dichotomy has its origins early in the history of Mars.

The giant impact hypothesis, originally proposed in the early 1980s, was met with skepticism due to the impact area's non-radial (elliptical) shape, where a circular pattern would be stronger support for impact by larger object(s). But a 2008 study[20] provided additional research that supports a single giant impact. Using geologic data, researchers found support for the single impact of a large object hitting Mars at approximately a 45-degree angle. Additional evidence analyzing Martian rock chemistry for post-impact upwelling of mantle material would further support the giant impact theory.

Human geography

From Wikipedia, the free encyclopedia
Jump to navigationJump to search
Original mapping by John Snow showing the clusters of cholera cases in the London epidemic of 1854, which is a classical case of using human geography

Human geography or anthropogeography is the branch of geography that is associated and deals with humans and their relationships with communities, cultures, economies, and interactions with the environment by studying their relations with and across locations.[1] It analyzes patterns of human social interaction, their interactions with the environment, and their spatial interdependencies by application of qualitative and quantitative research methods.[2][3]

Selenography is the study of the surface and physical features of the Moon. Historically, the principal concern of selenographists was the mapping and naming of the lunar maria, craters, mountain ranges, and other various features. This task was largely finished when high resolution images of the near and far sides of the Moon were obtained by orbiting spacecraft during the early space era. Nevertheless, some regions of the Moon remain poorly imaged (especially near the poles) and the exact locations of many features (like crater depths) are uncertain by several kilometers. Today, selenography is considered to be a subdiscipline of selenology, which itself is most often referred to as simply "lunar science." The word selenography is derived from the Greek lunar deity Σελήνη Selene and γράφω graphō, "I write".Geology of the Moon

From Wikipedia, the free encyclopedia
Jump to navigationJump to search
The geologic map of the Moon at 1-2.5M scale by Chinese Academy of Sciences.[1] See the original file for higher resolution.

The geology of the Moon (sometimes called selenology, although the latter term can refer more generally to "lunar science") is quite different from that of Earth. The Moon lacks a true atmosphere, which eliminates erosion due to weather. It does not have any known form of plate tectonics, it has a lower gravity, and because of its small size, it cooled faster. The complex geomorphology of the lunar surface has been formed by a combination of processes, especially impact cratering and volcanism. The Moon is a differentiated body, with a crustmantle, and core.

2:10
Smithsonian Institution Senior Scientist Tom Watters talks about the Moon's recent geological activity.
False-color image of the Moon taken by the Galileo orbiter showing geological features. NASA photo
The same image using different color filters

Geological studies of the Moon are based on a combination of Earth-based telescope observations, measurements from orbiting spacecraftlunar samples, and geophysical data. Six locations were sampled directly during the crewed Apollo program landings from 1969 to 1972, which returned 380.96 kilograms (839.9 lb) of lunar rock and lunar soil to Earth.[citation needed] In addition, three robotic Soviet Luna spacecraft returned another 326 grams (11.5 oz) from 1970 to 1976, and the Chinese robotic Chang'e 5 returned a sample of 1,731 g (61.1 oz) in 2020.[citation needed]

The Moon is the only extraterrestrial body for which we have samples with a known geologic context. A handful of lunar meteorites have been recognized on Earth, though their source craters on the Moon are unknown. A substantial portion of the lunar surface has not been explored, and a number of geological questions remain unanswered.

Elemental composition[edit source]

Elements known to be present on the lunar surface include, among others, oxygen (O), silicon (Si), iron (Fe), magnesium (Mg), calcium (Ca), aluminium (Al), manganese (Mn) and titanium (Ti). Among the more abundant are oxygen, iron and silicon. The oxygen content is estimated at 45% (by weight). Carbon (C) and nitrogen (N) appear to be present only in trace quantities from deposition by solar wind.

Lunar surface chemical composition[2]
CompoundFormulaComposition
MariaHighlands
silicaSiO245.4%45.5%
aluminaAl2O314.9%24.0%
limeCaO11.8%15.9%
iron(II) oxideFeO14.1%5.9%
magnesiaMgO9.2%7.5%
titanium dioxideTiO23.9%0.6%
sodium oxideNa2O0.6%0.6%
 99.9%100.0%
Neutron spectrometry data from Lunar Prospector indicate the presence of hydrogen (H) concentrated at the poles.[3]
Relative concentration of various elements on the lunar surface (in weight %)
Relative concentration (in weight %) of various elements on lunar highlands, lunar lowlands, and Earth

Formation[edit source]

For a long period of time, the fundamental question regarding the history of the Moon was of its origin. Early hypotheses included fission from Earth, capture, and co-accretion. Today, the giant-impact hypothesis is widely accepted by the scientific community.[4]

Transcript


Comments

Popular posts from this blog

Order up

The only book ever written by itself