Images of the near (left) and far side of the moon from NASA’s Clementine mission. Credit: NASA
A sample of lunar rock returned from a crater on the far side of the Moon by China’s Chang’e 6 spacecraft is helping astronomers understand why the 2 faces of our closest celestial neighbour are so different.
The far side of the Moon, most of which can never be seen from Earth, doesn’t look like the face which illuminates the night sky.
It has a thicker crust, more mountains and craters and fewer dark basalt patches formed by volcanic activity.
Professor Yang Li from the UK’s University College London and China’s Peking University, says, “The near side and far side of the moon are very different at the surface and potentially in the interior.”
“It is one of the great mysteries of the Moon. We call it the 2-faced Moon. A dramatic difference in temperature between the near and far side of the mantle has long been hypothesised, but our study provides the first evidence using real samples.”
The new study presents an analysis of 300g of the first ever sample taken from the far side of the Moon. It confirms previous findings which indicate the rocks are about 2.8 billion years old.
The researchers analysed the sample’s mineral composition and compared this to computer simulations to estimate how hot it was when it crystallised from molten lava to basalt billions of years ago.
They estimate the process occurred at about 1,000°C, about 100°C colder than estimated for samples collected from the near side of the Moon by the Apollo missions.
The ‘parent rock’, which initially melted into magma to later solidify into the rock sample collected by Chang’, also did so with a difference of 100°C compared to near-side rocks.
This temperature difference between the Moon’s faces may have been caused by an uneven distribution of elements such as uranium, thorium and potassium, which release heat due to radioactive decay, in the mantle.
The research has been published in Nature Geoscience.