Nasa's Grail mission has uncovered the origins of massive invisible regions with a strong gravitational pull that make the Moon's gravitational field so uneven.

The regions which were first discovered in 1968 are known as mass concentrations, or mascons, and are invisible to the naked eye. However, Grail (Gravity Recovery and Interior Laboratory) was able to monitor them using a combination of computer modelling and gravitational data collected by twin probes, Ebb and Flow.

"Grail data confirms that lunar mascons were generated when large asteroids or comets impacted the ancient Moon, when its interior was much hotter than it is now," said Jay Melosh, a Grail co-investigator and lead author of a paper on the subject published in the journal Science.

"We believe the data from Grail shows how the Moon's light crust and dense mantle combined with the shock of a large impact to create the distinctive pattern of density anomalies that we recognise as mascons."

At the centre of the impact site is a "gravity surplus" caused by lava filling the crater or an upswell from the iron-rich mantle layer. Around the gravity surplus area is a ring with a gravity deficit.

By understanding the effects of these ancient impacts on the Moon, scientists hope to discover more about plate tectonics and ore deposits on Earth as well as finding out how impacts might affect the formation of other planetary crusts in the solar system, such as those on Mars and Mercury.

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