Has the mystery of the Moon's dark side been solved? Scientists say face was formed by impact of massive asteroid

  • Japanese team say the giant cosmic impact created a magma sea more than a thousand miles wide and several hundred miles deep
  • Theory explains why moon's near and far sides are so different
  • Asteroid an estimated 180 miles in diameter; impact nearly 4bn years ago

The largest lunar dark spot, a massive 1,800 mile wide (3,000 kilometres) crater known as the 'Ocean of Storms', may be a scar from a giant cosmic impact, researchers believe.


These findings could help explain why the moon's near and far sides are so very different from one another, the team say.

The two sides of the moon: Researchers now believe Procellarum, the largest of the three massive impact basins shown here, was formed by a massive cosmic collision

'Our discovery provides the first compositional evidence of this idea, which could be confirmed by future lunar sample return missions, such as Moonrise, a proposed NASA mission that would send an unmanned probe to collect lunar dirt and return it to Earth,' lead study author Ryosuke Nakamura, a planetary scientist at the National Institute of Advanced Industrial Science and Technology in Tsukuba, Japan, told SPACE.com.

'The neighboring Earth likely experienced similar-sized impacts around the same period,' Nakamura added.

'It would have had a great effect on the onset of Earth's continental crust formation and the beginning of life.'

Scientists analyzed Oceanus Procellarum, or the Ocean of Storms, a dark spot on the near side of the moon more than 1,800 miles (3,000 kilometers) wide.

Researcher already know the near side of the moon, the side that always faces Earth, is quite different from the far side (which is often called the dark side, even though it does get sunlight).

Previous studies have found widespread plains of volcanic rock called 'maria' cover nearly a third of the near side, but only a few maria are seen on the far one.

Now scientists in Japan say that a giant collision may also explain the moon's two-faced nature, one that gave rise to the Ocean of Storms.

The size of the asteroid involved is estimated at 180 miles in diameter, and it is believed it hit the moon's surface 3.9billion years ago.

Researchers analyzed the composition of the moon's surface using data from the Japanese lunar orbiter Kaguya/Selene. 

These data revealed that a low-calcium variety of the mineral pyroxene is concentrated around Oceanus Procellarum, the Ocean of Storms, and large impact craters such as the South Pole-Aitkenand Imbriumbasins.

This type of pyroxene is linked with the melting and excavation of material from the lunar mantle, and suggests the Ocean of Storms is a leftover from a cataclysmic impact.

This collision would have generated 'a 3,000-kilometer (1,800-mile) wide magma sea several hundred kilometers in depth,'

The red points show high low-calcium pyroxene concentrations, discovered through data mining of Kaguya's spectral data archive, and are signs of a cosmic impact.

The researchers believe collisions large enough to create Oceanus Procellarum and the moon's other giant impact basins would have completely stripped the original crust on the near side of the moon.

The crust that later formed there from the molten rock left after these impacts would differ dramatically from that on the far side, explaining why these halves are so distinct.

The scientists detailed their findings online Oct. 28 in the journal Nature Geoscience.

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