杏吧原创

FOR thousands of years, people gazing at the lunar surface have seen a 鈥渕an in the moon鈥�. Now we know how he got there.

Some 4 billion years ago, when the moon was still geologically active, the far side of the moon was battered by asteroids, says Ralph von Frese of Ohio State University. The resulting shock waves were so strong that they triggered volcanic eruptions on the side we can see by opening up cracks in the crust through which magma flooded onto the surface. This solidified to form what we now see as the eyes, nose and mouth of the man in the moon (Physics of the Earth and Planetary Interiors, vol 153, p 165).

Von Frese and colleague Laramie Potts created a topographical model of the moon and mapped the gravity signatures of rocks all the way to the core, using measurements taken by NASA鈥檚 Clementine and Lunar Prospector satellites.

Their findings show that the impacts of the ancient collisions raised a bulge on the near side that was further tugged by Earth鈥檚 gravity. That gravity anomaly is still measurable today. 鈥淭he impacts were huge enough to disrupt the moon to its core,鈥� says von Frese.

Cross-sectional images of the interior show that part of the mantle, the zone beneath the crust, has been pushed into the core, 1100 kilometres beneath the impacts on the surface.