Research led by the VU University Amsterdam suggests much of the hot, molten rock in the moon's deep interior is so dense it is simply too heavy to rise to the surface, scientists said.
The scientists produced microscopic copies of moon rock collected by the Apollo missions, melted them at the extremely high pressures and temperatures found inside the moon, and then measured their densities with powerful X-rays, a release from the European Synchrotron Radiation Facility reported Sunday.
Vertical movement of magma is driven by the density difference between the magma and the surrounding solid material, researchers said, making the liquid magma move slowly upward like a bubble.
The lighter the liquid magma the faster the upward movement, they said, but much of the moon's magma is a titanium-rich type as dense as the rocks found in the deepest parts of the lunar mantle today.
This magma would not move toward the surface, they said, although that could change in the future.
"In the distant future, the cooler and therefore solidifying melt will change in composition, likely making it less dense than its surroundings," researcher Win van Westrenen said. "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."