South Pole-Aitken basin: Facts, Discussion Forum, and Encyclopedia Article

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South Pole-Aitken basin

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	Topics South Pole-Aitken basin Topic Home The South Pole-Aitken basin is an impact craterImpact crater Summary An impact crater is a circular or oval depression on a surface, usually referring to a planet, moon, asteroid, or other cel... on EarthEarth Earth is the third planet in the solar system in terms of distance from the Sun, and the fifth largest.... 's MoonMoon The Moon is Earth's only natural satellite.... . Roughly 2500 kilometers in diameter and 13 kilometers deep, it is the largest known impact crater in the entire solar system. The only impact basin close to it in size is the 2100 kilometer Hellas PlanitiaHellas Planitia Hellas Planitia, also known as the Hellas Impact Basin, is a roughly circular impact crater located in the southern he... on Mars. This basin was named for two features on opposing sides; the Aitken craterAitken (crater) Aitken is a large lunar impact crater that lies on the far side of the Moon.... on the northern end and the southern lunar pole at the other end. The outer rim of this basin can be seen from Earth as a huge chain of mountains located on the lunar southern limb, sometimes called "Leibnitz mountains", although this name has not been considered official by the International Astronomical UnionInternational Astronomical Union The International Astronomical Union unites national astronomical societies from around the world.... . Discovery The existence of a giant far side basin was suspected as early as 1962 based on early probe images (namely Luna 3Luna 3 The dramatic first pictures of the unseen far side of the moon were sent to earth by the Soviet Union spacecraft, Luna 3, in... and Zond 3Zond 3 Zond 3, a member of the Soviet Zond program, was the first Zond spacecraft to successfully complete its mission and took a n... ), but it was not until the acquisition of global photography by the Lunar Orbiter programLunar Orbiter program The Lunar Orbiter program was a series of five unmanned Lunar orbiter missions launched by the United States in 1966 through... in the mid-1960s that geologists recognized its true size. Laser altimeter data obtained during the Apollo 15 and 16 missions showed that the northern portion of this basin was very deep, but since these data were only available along the near-equatorial ground trackGround track A ground track or ground trace is the projection of a satellite's orbit onto the surface of the Earth .... s of the orbting Command and Service Modules, the topography of the rest of the basin remained unknown. The first complete geologic map showing the confines of this basin was published in 1978 by the United States Geological SurveyUnited States Geological Survey border="1" cellpadding="2" cellspacing="0">... . Little was known about the basin until the 1990s, when the spacecraft Galileo and ClementineClementine mission Clementine was a joint space project between the Ballistic Missile Defense Organization and NASA.... visited the Moon. Multispectral images obtained from these missions showed that this basin contains more FeO and TiO₂Titanium dioxide Titanium dioxide, also known as titanium oxide or titania, is the naturally occurring oxide of titanium, chemica... than typical lunar highlands, and hence has a darker appearance. The topography of the basin was mapped in its entirety for the first time using altimeter data and the analysis of stereo image pairs taken during the Clementine missionFacts About Clementine mission Clementine was a joint space project between the Ballistic Missile Defense Organization and NASA.... . Most recently, the composition of this basin has been further constrained by the analysis of data obtained from a gamma-ray spectrometer that was onboard the Lunar ProspectorLunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery P... mission. Physical characteristics The lowest elevations of the Moon (about -6 km) are located within the South Pole-Aitken basin, and the highest elevations (about +8 km) are found on this basin's north-eastern rim. Because of this basin's great size, the crust at this locale is expected to be thinner than typical as a result of the large amount of material that would have been excavated during this impact event. Crustal thickness maps constructed using the Moon's topography and gravity field imply a thickness of about 15 km beneath the floor of this basin, in comparison to the global average of about 50 km. The composition of this basin, as estimated from the Galileo, ClementineClementine mission Overview Clementine was a joint space project between the Ballistic Missile Defense Organization and NASA.... and Lunar ProspectorFacts About Lunar Prospector The Lunar Prospector mission was the third selected by NASA for full development and construction as part of the Discovery P... missions, show that it is different than typical highland regions. Most importantly, none of the samples obtained from the American ApolloProject Apollo Project Apollo was a series of human spaceflight missions undertaken by the United States of America using the Apollo space... and Russian LunaLuna programme The Luna programme was a series of unmanned space missions sent to the Moon by the Soviet Union between 1959 and 1976.... missions, nor the handful of identified lunar meteorites, have a composition that is comparable. The orbital data indicate that the floor of this basin has slightly elevated abundances of iron, titanium, and thorium. In terms of mineralogy, the basin floor is much richer in clinopyroxene and orthopyroxene than the surrounding highlands that are largely anorthositic. Several possibilities exist for this distinctive chemical signature. One is that this composition might simply represent lower crustal materials that are somewhat more rich in iron, titanium and thorium than the upper crust. Another possibility is that this composition reflects the widespread distribution of ponds of iron-rich basaltBasalt Basalt is a common gray to black volcanic rock.... s, similar to those that make up the lunar mariaLunar mare The Lunar maria are large, dark, basaltic plains on Earth's Moon, formed by ancient basaltic flood eruptions caused by extre... . Alternatively, the rocks here could contain a component from the lunar mantle if the basin excavated all the way through the crust. The origin of the anomalous composition of this basin is not known with certainty at this time, however, and a sample return mission will most likely be required to settle this debate. Complicating matters is the fact that all three of the above hypotheses could contribute to the anomalous geochemical signature of this giant crater. Furthermore, it is possible that a large portion of the lunar surface in the vicinity of this basin was melted during the impact event, and differentiation of this impact melt sheet could have given rise to additional geochemical anomalies. Origin Simulations of near vertical impacts show that this basin should have dug up vast amounts of mantle materials from depths as great as 200 km below the surface. However, observations thus far do not favor a mantle composition for this basin, and crustal thickness maps seem to indicate the presence of about 10 kilometers of crustal materials beneath this basin's floor. This has suggested to some that the basin was not formed by a typical high-velocity impact, but may instead have been formed by a low-velocity projectile that hit at a low angle (about 30 degrees or less), and hence did not dig very deeply into the Moon. Putative evidence for this comes from the high elevations north-east of the rim of the South Pole-Aitken basin that might represent ejecta from such an oblique impact. External links