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Oct 13th
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The Lunar Lowdown


moonSLUG REPORT > UCSC researchers unveil new theory about the moon

Pink Floyd may have sung about the dark side of the moon, but UC Santa Cruz planetary scientists have made an important new insight into the far side of the moon.

The lunar hemisphere that is permanently turned away from Earth is dramatically different from the part facing the planet. Its crust is much thicker than the near side’s, and the terrain is more jagged and varied. UCSC professor of Earth and planetary sciences Erik Asphaug explained that the new study theorizes that the moon was at some point struck by a smaller piece of matter that created the upset in the far side’s surface.

This goes along with the “giant impact” model, which puts forth the idea that the moon was originally created by the debris of a Mars-sized object striking Earth. The smaller body that later struck the moon may have been another piece of debris from the first collision.

"Our model works well with models of the moon-forming giant impact, which predict there should be massive debris left in orbit about the Earth, besides the moon itself,” said Asphaug in an Aug. 1 press release from UCSC. “It agrees with what is known about the dynamical stability of such a system, the timing of the cooling of the moon, and the ages of lunar rocks."

Ausphaug coauthored a paper with UCSC postdoctoral researcher Martin Jutzi that will appear in the Aug. 4 issue of Nature. Jutzi said in the press release that it’s no coincidence that the far side is the part with craters, but that it has to do with balance.

"The collision could have happened anywhere on the moon," he said. "The final body is lopsided and would reorient so that one side faces Earth."

The new study challenges a theory, previously put out by UCSC colleagues Ian Garrick-Bethell and Francis Nimmo, that the surface of the moon has more to do with tidal forces than anything else. In the press release, Nimmo said he still wasn’t sure what to believe, but praised Asphaug and Jutzi’s “elegant” article. He also stressed that the absolute truth is still a mystery.

"The fact that the near side of the moon looks so different to the far side has been a puzzle since the dawn of the space age, perhaps second only to the origin of the moon itself," he said. "As further spacecraft data (and, hopefully, lunar samples) are obtained, which of these two hypotheses is more nearly correct will become clear.”


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