News A Volcano on the Moon — Where None Should Be

jason

Seanchaí
Staff member
Human beings have been staring at the moon since long before we were human beings at all. Far back in biological history, some light-sensitive eyespot on some prehuman thing must have first registered the shimmer of moonlight, and the lunar love affair began.
For most of the eons that have passed since then, we only looked at part of the moon — the half that is eternally pointed toward Earth. It wasn't until 1968, during the flight of Apollo 8, that the first modern human eyes got an in-person look at the mysterious far side. (See TIME's special report on the 40th anniversary of the moon landing.)
The differences between the two hemispheres could not be clearer. While the facing side of the moon features vast, dark plains of cooled lava — which the ancients assumed were seas — the far side is mostly an expanse of tens of thousands of impact craters. It is the tug of the Earth, astronomers believe, that is responsible for the different topography. Earthly gravity pulls with greater force on the dense, iron-and-magnesium interior of the moon than on the lighter upper layers. This causes the core to shift slightly earthward, thinning out the crust on that half of the moon. Volcanoes or meteor impacts on the near side could thus cause more copious lava bleeds, which spread out across the surface and form plains. The far side had a tougher hide and was thus less easily damaged.
 
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