Earlier this week, a group of scientists working at the VU Amsterdam University in the Netherlands conducted an experiment in which they learned how the Moon’s interior is truly structured: below the thin rocky surface (otherwise known as a lithosphere) churns a thick mantle of liquid magma.

The team was led by Mirjam van Parker and Wim van Westrenen and consisted of scientists from the Universities of Paris 6/CNRS, Lyon 1/CNRS, Edinburgh, and the European Synchrotron Radiation Facility (ESRF) in Grenoble, France. Using copies of 380 kilograms worth of lunar rock samples that were collected by the astronauts from the Apollo missions, the scientists melted them with a high electric current at a temperature of 1,500˚F, then compressed them at a pressure of 4,500 bar. The aforementioned temperature and pressure are thought to be at the same intensity as the ones underneath the Moon’s surface.

After this, the team measured the samples’ density with powerful x-ray beams emitted from a synchrotron, provided by the ESRF. They learned that the molten rock (the magma) was quite dense – much denser than they had assumed – and that it was liquid, filled with titanium.

These results have disproven a commonly referenced hypothesized cross-section that scientists constructed in the past: first is the thin crust, which is not uniform in thickness around the surface; below is a thick, solid mantle; following is a thinner mantle known as the moonquake zone, which is slightly less solid than the upper mantle, so that seismic waves can travel; and, finally, a solid iron-rich core lies in the center.

The Moon lacks current volcanic activity because the magma is too dense, or just a bit too firm; lighter liquid tends to be pushed up more, similar to the magma under the Earth, and there must be a difference in density between the magma and the surrounding solid material for any eruptions.

“Today, the Moon is still cooling down, as are the melts in its interior,” Wim van Westrenen, the chair of the Netherlands Platform for Planetary Science, states in the ESRF’s news release. “In the distant future, the cooler and therefore solidifying melt will change in composition, likely making it less dense than its surroundings.

This lighter magma could make its way again up to the surface forming an active volcano on the Moon – what a sight that would be! – but for the time being, this is just a hypothesis to stimulate more experiments.” He and Mirjam van Parker have published the findings of their experiment in the journal, ‘Nature Geosciences’, on February 19.

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