The Moon’s biggest scar may be hiding something even stranger than the impact that made it. Deep beneath the South Pole-Aitken basin on the lunar far side, scientists have identified a huge mass of unusually dense material, preserved far below the surface and still weighing down the basin floor.
That finding points to a violent chapter from the solar system’s early history, and to a lunar interior that may have stayed more stable than many researchers expected.
The South Pole-Aitken basin is enormous, the largest preserved impact basin on the Moon and one of the oldest. It stretches roughly 2,000 kilometers across, sits on the far side, and records a collision from about 3.9 to 4.3 billion years ago, when impacts were still reshaping the inner solar system. Unlike Earth, whose surface has been reworked by plate tectonics, erosion, and volcanism, the Moon has kept many of those ancient scars intact.
Now one of those scars appears to hold a clue buried in the mantle below.
Hellbound and Down 