Mascons or gravitational anomalies of the Moon

Mass concentrations of the Moon

The Moon is the only celestial body on which the man is gone, and yet it is not so friendly as you might think. There is absolutely no air, so you need a pressure suit any leakiness of the combination exposes astronauts to deadly empty. It is also a world of silence, the sound can not be transported unless the use of radio transmitters and headphones. As there is no atmosphere, sunlight is filtered and then the sky is always black. In addition there is no color, the landscape is sad, it is the same everywhere in a more or less monotonous gray tone. Temperatures are extremely inhospitable, the transition from hot to cold is especially brutal, 132 ° C during the day to -151 ° C at night. And finally the absence of a magnetic field passes deadly solar radiation. Many meteorites collide with the lunar surface at high speed without being slowed down, for 4 billion years, they spray the moon rock, creating over a layer of fine dust, regolith. The dust is so fine that it presents a danger, it sticks on the combinations of instruments and would be a big problem if we had to live on the moon.
The Moon, like all celestial bodies, is not a perfectly spherical object and its internal structure is not formed of homogeneous layers of equal thickness. As on Earth, gravity varies from the place where it is measured. By measuring variations in gravity around the Moon, we can determine the density variations and deduce its internal structure. Gravitational anomalies of the Moon are caused by concentrations of huge masses called "mascons".

NB: The regolith means the layer of dust produced by the impact of meteorites on the surface of a planet or a satellite without atmosphere.

The mascons are irregularly distributed in the subsoil especially in the lunar maria. These local density increases or mascons, discovered around 1970, disrupt the trajectories of probes in orbit around the Moon. GRAIL both probes have shared the same orbit, separated from each other by a distance determined by scientific measurement according to their needs. This distance once determined (between 75 and 225 km) depends on the gravitational field. Continuously measuring the spacing, the two probes detect with high accuracy deficiencies lunar gravity field. With this density measurement, the average thickness of the lunar crust has been estimated between 34 and 43 km, thinner 10 to 20 km than what was expected. This feature shows that the composition of the Moon resembles Earth. Thus, the most accepted hypothesis for the formation of the Moon, that a giant impact between the young Earth and an object the size of Mars, is strengthened. This episode date of 4.2 billion years, in 2009 this is the age that a team of researchers has given to the Moon.

NB: In general, the word "mascon" can be used as a substantive to refer to excessive mass distribution on or under the surface of a planet. Examples of types of MASCON basins on the Moon are the impact basins, Mare Imbrium, Mare Serenitatis, Mare Crisium and Mare Orientale, which have significant topographic depressions and positive gravitational anomalies. Examples of types of basins on Mars are MASCON basins, Argyre Planitia, Isidis Planitia and Utopia Planitia.

Image: Lunar mapping, this graph shows the apparent density of the lunar mountains generated from gravity data of the GRAIL mission and topographic data Lunar Reconnaissance Orbiter from NASA. Red corresponds to higher than average densities and the blue is lower than the average densities, white denotes regions that have not been analyzed. The average bulk density is 2550 kg per cubic meter. Filled circles correspond to major impact basins. The largest basin on the hemisphere of the dark side of the moon, the Pole-Aitken South Basin, has a density greater than the average reflecting its iron-rich composition. Each image covers 75 percent of the lunar surface. Credit image: NASA / JPL-Caltech / IPGP

The mystery of gravitational anomalies

The GRAIL mission NASA has discovered the origin of the invisible regions which explains the massive gravitational anomalies of the moon. Concentrations of unequal masses affect operations lunar spacecraft navigating in orbit around the Moon. The findings of GRAIL will in the future allow satellite mission to navigate more accurately. The twin GRAIL satellites studying the internal structure and composition of the Moon with unprecedented detail, since August 2012. They identified the locations of large dense regions called mass concentrations or mascons, which are characterized by a stronger gravitational attraction. The mascons are hidden beneath the lunar surface and can not be seen by normal optical cameras. Scientists from the GRAIL mission found the mascons combining gravity data GRAIL with sophisticated computer models concerning large asteroid impacts and the known details of the geological evolution of impact craters.
The results are published in the May 30, 2013 edition of the journal Science.
"The data confirm that the lunar mascons occurred when asteroids or comets hit the old Moon, when the interior was much warmer than today," said Jay Melosh, a co-investigator on the GRAIL Purdue University in West Lafayette, Indiana, and lead author of the article. The origin of lunar mascons is a mystery in planetary science, since their discovery in 1968 by a team from the Jet Propulsion Laboratory of NASA in Pasadena, California.

The model shows that the gravitational surplus is a natural consequence of the shock that produced the crater excavation, collapse and cooling due to the impact. The increase in density and thus the center of gravity of the target mascon is caused by lunar material melted by the heat of an asteroid impact, a long time ago. Our planet has suffered similar impacts in the distant past, and understanding mascons we can learn more about the ancient Earth, perhaps how plate tectonics began and what created the first ore.
The GRAIL A and GRAIL B probes, renamed Ebb and Flow, were launched on 10 September 2011. They analyzed on the same nearly circular orbit near the poles of the Moon at an altitude of about 55 km, the lunar surface until the end of their mission. Driven by teams of NASA, they crashed on the moon, near the crater Goldschmidt, December 17, 2012. There was no picture of the impact because the impact area was located in a dark area. The distance between the twin spacecraft has changed slightly during their mission as they flew over areas of greater or lesser gravity caused by visible features such as mountains and craters and by masses hidden concentrations in the lunar surface.

Image: The twin spacecraft Ebb and Flow of GRAIL Mission (Gravity Recovery And Interior Laboratory). The main objectives of the mission were to know the internal structure of the Moon from the heart to the crust, and get a detailed understanding of the thermal evolution of the Moon. Ebb and Flow took more than 115,000 pictures of the Moon and collected a lot of data on its gravitational field. These data will nourish analyzes scientists for many years. Credit image: NASA / JPL-Caltech / MIT

Mare Orientale

This huge crater drawn on the surface of the moon is called Mare Orientale is one of the most impressive basins lunar crater, with its large size. It is located in the extreme west of the visible face, it is therefore difficult to see from Earth.
This mosaic of images of the ringed structure of large lunar impact basin reveals startling details. This mosaic is made up of images taken by the Wide Angle Camera of the lunar probe LRO (Lunar Reconnaissance Orbiter).
These images do not overlap all completely, which explains the visible black lines primarily on the right side of the image. Partially submerged by lava flows, Mare Orientale is older than 3 billion years old and has about 950 km in diameter.
Its formation is due to the fall of a large asteroid that was undulate the lunar crust concentrically like a stone falling into water. Although the Moon is barren and devoid of atmosphere, the dark regions on the surface of the Moon were called mare, i.e. "sea" in Latin. Early astronomers believed that these regions could indeed be large expanses of water.

Plutarch (46-125) thought that the moon was a heavenly Earth, and the dark areas were regular and plains filled with water, called Maria (Latin word meaning seas plural). Highlands, clear color were baptized, Terrae.

Image: mosaic images of the ringed structure of large lunar Mare Orientale impact basin.
Credit: NASA / GSFC / Arizona State Univ. / Lunar Reconnaissance Orbiter