Saturday, June 13, 2009

The different gravity anomalies of the lunar Near and Far Sides

The nearside on the left, and the farside on the right. Red
indicates strong gravity (positive gravity anomalies), and
blue indicates weak gravity (negative gravity anomalies).
Anomalies differ on the near and far sides.

Prof. Manabu Kato
Science Manager of Kaguya

"On the nearside they are made up of heavy materials, and contain mascons (mass concentrations) that are positive gravity anomalies - i.e., the local gravity is stronger than average. Hypothetically, when a celestial body hit the Moon's surface, the temperature and pressure of the lunar interior increased, and the softened and easily distorted interior material pushed up the mantle, causing the eruption of high-density lava and producing a mascon. On the farside, on the other hand, there are few lunar maria. The farside has no mascons - positive gravity anomalies - but rather a number of negative gravity anomalies in craters and basins, which are all topographically round-shaped. Scientists believe that on the farside, the interior of the Moon was at lower temperatures and thus more firm. As a result, when large celestial objects impacted the Moon and impact basins were formed, there was less crustal uplift and lava eruption, and thus no density anomalies."

"KAGUYA's gravity measurements suggest that approximately 4 billion years ago, when most of the Moon's impact topography (craters, basins and maria) was formed, its interior was hot on the nearside but cold on the farside, resulting in the variation in the firmness of the crust on the near and far sides."

Read the JAXA feature story HERE.