What if the moon is hollowed out

astronomy: The moon's crust is more battered than expected

The lunar crust is up to 43 kilometers thick and criss-crossed by deep invisible magma channels. This is shown by observations of the Grail lunar mission of the US space agency NASA. The total of at least 5,300 kilometers long frozen inclusions are believed to have arisen when the young moon expanded, write researchers working with Jeffrey Andrews-Hanna from Colorado's University of Mining in Golden (USA) in the magazine Science .

The underground channels made themselves felt in the measurement data due to their greater gravity. Grail (Gravity Recovery and Interior Laboratory) has been measuring the gravitation of the earth's satellite in detail since last year. The mission consists of two probes orbiting the moon. The twin probes measure fluctuations in the distance between them, which are triggered by the slightly different gravity of the lunar regions overflown. In this way, different surface features such as craters or mountains can be made visible as well as fluctuations in mass below the surface of the moon.

The probes have now discovered a total of 22 dead straight channels of solidified magma under the crust. They have a greater density than the surrounding lunar soil and ensure that where they run, there is a higher force of gravity. The inclusions are believed to be over four billion years old. For the first time they allow a glimpse into the early phase of the moon's development.

The kilometer-deep formations are the first evidence for the theory that the radius of the young moon initially expanded thermally by 0.6 to 4.9 kilometers before it later contracted moderately. The traces of the development of the young moon were wiped from the surface by countless cosmic impacts, so this phase has not yet been accessible to observation.

The lunar crust itself is significantly less massive than expected, as the Grail data also show. The upper lunar crust weighs around 2.5 tons per cubic meter, which is 300 to 400 kilograms less than assumed.

Probably the crust of the earth's satellite is twelve percent more porous than expected, researchers around Mark Wieczorek from the Paris Sorbonne also write in Science . According to the measurements, the lunar crust is 34 to 43 kilometers thick. This corresponds roughly to the thickness of the continental crust. However, the scientists had expected it to be much wider. Now it is clear that under many deep craters on the surface there is hardly any solid rock left. Early asteroid impacts practically hollowed out the outer rock shell of the earth's satellite in these places.