The Moon was once covered in an ocean of magma

Data from India’s Pragyan lunar rover points to the existence of an ancient ocean of magma on our Moon.

Pragyan emerged from the Vikram lander which touched down in August last year near the Moon’s south pole as part of the Indian Space Research Organisation’s Chandrayaan-3 mission. It gives lunar researchers a new perspective as other samples of Moon soil have come from equatorial to mid-latitudes.

Analysis of Pragyan’s 23 measurements taken over a 103-metre distance is published in a paper appearing in Nature.

Pragyan used its on-board alpha particle X-ray spectrometer to assess the composition of the Moon’s regolith – the layer of loose stone and dust which sits on top of the bedrock.

The analysis shows the lunar regolith is fairly uniform, primarily made up of the rock ferroan anorthosite. The amount of this rock found by Pragyan sits somewhere between the amounts found at the equator by the Apollo 16 and Luna-20 missions.

Similar chemical composition across wide areas, the authors argue, suggests that the Moon was once covered by an ocean of magma.

This “lunar magma ocean” hypothesis suggests that the Moon started off very hot billions of years ago – hot enough to have liquid rock on its surface. Then, as it cooled, less dense ferroan anorthosite rocks floated to the surface, while heavier minerals sank to form the Moon’s mantle.

One roadblock for this theory is the fact that Pragyan also found heavier magnesium minerals which can’t be explained by the lunar magma ocean.

But the authors suggest that these minerals could have been brought to the surface by the event which created the nearby South Pole-Aitken basin.

This is a massive impact crater 6.2–8.2km deep and about 2,500km wide, meaning it covers about 13% of the Moon’s total surface area. It is one of the largest impact craters in the solar system and is believed to have been formed 4.2 to 4.3 billion years ago by an object about 200km across.