Is the “Giant Impact Hypothesis” still considered to be the best explanation for how the moon came into being?

Yes.  The current experiments and modeling efforts predominantly use the giant impact hypothesis as the basis of their studies.  In other words, approximately 4.5 billion years ago, a collision of the early Earth with a Mars-sized object resulted in the formation of the Earth/Moon system.  This model provides answers to the reasons behind the Earth/Moon high-spin system, the low density of the Moon, and lunar composition.  Other hypothesis on lunar formation are that a planetoid (the Moon) was captures in the Earth’s gravity well, or that the Earth and Moon co-formed together through accretion.  Neither of these explanations provide quite the full picture that the giant impact does, however.

Brad Bailey

NLSI Staff Scientist

January 20, 2009

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Only about 59 percent of the moon's surface is visible to us here on earth.

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