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(47,953 posts) Fri May 31, 2013, 08:17 PM May 2013

Revealed: The Awesome Explanation for the Moon’s Extra Gravity

By Michael Lemonick

In 1968, just a year before the historic Apollo 11 Moon landing, NASA scientists discovered something that could have sent astronauts Neil Armstrong, Buzz Aldrin and Michael Collins plunging to their deaths: an unexpected gravitational force—one so strong it caused the unmanned Lunar Orbiter spacecraft to violently shake up and down as it orbited Earth’s neighbor.

The cause, NASA determined, was the presence of “mascons,” or mass concentrations of especially dense rock just below the surface of the Moon, with much stronger pulls than the rock that surrounds them. Scientists adjusted accordingly to land the Apollo. But for decades, a pressing question lingered: how could these mascons—not found anywhere on Earth—even exist in the first place?

Today, as published in Science, we finally have an answer. In short: blame the asteroids—and the make-up of the Moon itself.

Mascons are always found within impact basins, the huge, roughly circular depressions created when asteroids smashed into the Moon billions of years ago. Since the depressions are lower than the surrounding surface, and therefore hold less rock, you’d naturally expect less gravity in these locations. But there’s actually more.

That’s because the Moon is made like lemon-meringue pie. No, really. As Science paper co-author and planetary scientist Jay Melosh explains, the crustal rock on the surface has a relatively low density, like meringue. And the mantle underneath is like lemon filling—it’s denser than what’s on top, and warm enough to flow under pressure (even though it’s technically solid). When asteroids strike, they blast through the Moon meringue and drill deep into its lemon filling.

Read more: http://science.time.com/2013/05/30/revealed-the-awesome-explanation-for-the-moons-extra-gravity/