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Moon, Saturn, and Antares

March 12, 2015

A bright triangle adorns the early morning sky tomorrow: the Moon, the planet Saturn, and the star Antares. Saturn is to the right or upper right of the Moon at first light, with fainter Antares about the same distance to the lower right of the Moon.

Like Earth, the Moon is made of a series of layers: a dense core made of iron and nickel, a surrounding mantle of lighter-weight rock, and a thin crust of even lighter materials. But some of the details have been the subject of debate. In particular, scientists haven’t been quite sure whether any part of the interior is still molten.

A recent study suggests that the inner part of the mantle is still hot and molten — a result of Earth’s gravitational pull.

An international team reached that conclusion after studying observations from several spacecraft in lunar orbit, as well as other experiments. A spacecraft’s orbit is changed by tiny variations in the Moon’s gravitational field, which can reveal details about the interior.

The study concluded that the part of the mantle that surrounds the core is still at least partially molten. It’s heated by Earth’s gravitational pull, which creates tides in the solid Moon just as lunar gravity causes ocean tides here on Earth. The tides cause the Moon’s interior to stretch and twist. That motion is converted to heat, which melts some of the rock hundreds of miles below the surface — and keeps the Moon from being a completely dead world.


Script by Damond Benningfield, Copyright 2015

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