Mass concentration (astronomy)

Mascons are large scale areas of increased density rock below the surface of the moon. The most massive of them are in the range of the big round moon seas in the northern hemisphere. The name was derived from the English word for mass concentration (mass concentration).

The density within a mascons is 3.3 g / cm ³ for the surrounding rock, however, at 3.0 g / cm ³. The mass of all mascons makes about 0.01 to 0.03 percent of the total mass of the moon. As negative mascons areas are referred to that have a lower density than the surroundings.

The largest mascons

The five most important mascons below the big round moon seas on the near side ( in the picture above, the red areas). Smaller mascons there on the moon back negative (blue areas) under some very large impact craters.

The places on the extent of mascons ranked:

Negative mascons ( mass deficits) characterize many Wall plains and large craters:

  • In the southern highlands Wall levels Bailly, Schickard, Clavius ​​and adjacent large crater as Longomontanus and Maginus
  • äquatornah on the highlands of the Moon back & a Hertzsprung and Mendeleev
  • And in the southern highlands of the Moon back & a Tsiolkovskiy and - within the South Pole - Aitken basin - the large crater Apollo and Schrödinger

Discovery history

Already with the first lunar probes orbiting the moon ( Lunar Orbiter ) perturbations were discovered in the form of regionally stronger path curvature, indicating the astronomers to disturbances in the distribution of mass of the moon. Only a spherically symmetric mass distribution orbiting a satellite the celestial body in an elliptical orbit, the irregular rounds of the probes could thus only be explained with gravity anomalies. Later, the Lunar Prospector mission - charted these areas and created a detailed map of mascons.

Formation theories

Since mascons below of impact craters and Mary, their origin goes back to the time of the Last Great bombardment before about 4 to 3.8 billion years back. Huge meteorite fell in this era to the moon and broke through the rocky crust. The rising magma spilled out onto the lunar surface, thus shaping the Mary, below the mascons emerged. Some believe that the mascons are remnants of the iron cores of these meteorites, others go from lava bubbles from that arose as a result of the strikes.

Measurements of the Apollo missions suggest, however, that the circular basin were first partially filled with magma. These masses of basalt ( rock density 3.3 g / cm ³ ) decreased in the surrounding crustal rocks ( 2.9 to 3.4 g / cc) in until isostatic equilibrium was reached. The layer package then froze, so later basalt effusions, which filled up the Mary to the present level, no longer came to isostasy and now represent mass surpluses. In the center of the round Maria the basalt layer is about 25 km thick, the edges takes them off.

The irregularly shaped moon seas, however, have no mascons and are less deep. You are probably arose simultaneously with the uppermost lava flows round Mary, overflowing there.

Mascons on Earth

Below the large impact craters on Earth, such as under the Ries no mass concentrations have been detected. It is believed that the heated core on impact vaporized by air in the atmosphere or the debris at impact distributed over a large area. The earth's crust ranges much lower than the earlier lunar crust and was not hit as in the genesis of Mare basin. In Antarctica in Wilke country has a large gravity anomaly was discovered in 2006, which could be a Mascon.