A large block of granite that was slowly releasing heat has been discovered buried under a crater on the Moon. This isn’t science fiction, it’s an ancient volcano. The moon had lava fields and volcanic eruptions, but astronomers didn’t actually find a more typical Earth-like volcano–until they looked at what was beneath the Compton and Belkowitz craters on the far side of the moon.
Granite is not very common outside of Earth, so finding it on the Moon is very exciting. On our planet, they form deep below the surface, usually under a volcano where magma can cool and crystallize. To make granite, the presence of water and plate tectonics helps a lot. The team used a combination of data from Chinese and US lunar orbiters to detect this heat-emitting mass beneath the surface, identifying an unprecedented volcanic process on the Moon.
“Using an instrument that looks at microwave wavelengths — longer than infrared — sent to the moon on both the Chinese orbiters Chang’E 1 and 2, we were able to map subsurface temperatures. What we found is that one of these suspected volcanoes, known named Compton-Belkowitz, it was just as glowing at microwave wavelengths, said lead researcher Matt Siegler, of the Planetary Science Institute, in statement.
“What this means is that it’s hot, not necessarily on the surface, as you can see in the infrared, but below the surface. The only way to explain that is from the extra heat coming from somewhere below the feature within the deep lunar crust. So Compton Belkowitz, who It is believed to be a volcano, which also hides a large source of heat beneath it.
Evidence of a new volcanic process has been discovered on the moon.
Image credit: Siegler at al, Nature July 2023
The data shows a 20-kilometre (12-mile) wide silicon-rich surface that they believe is the caldera of this ancient volcano. The temperature there is 10 degrees Celsius (18 degrees Fahrenheit) warmer than the surrounding areas, but it’s not from magma below the surface – the last time the volcano erupted was 3.5 billion years ago – it’s from radioactive elements that were stuck in the rock.
“We interpret this convective flow as being caused by a granite body rich in radioactive material below the caldera,” Dr. Siegler said. He said. “To tell the truth, we were a little baffled when we found it: Fortunately, my wife, Dr. Rita Economos, is a geochemist in the family, so with her guidance, we were able to piece together a possible geological cause of the thermal anomaly.”
As Dr. Economos explains: “This discovery is a 50 km wide bath chamber; Batholith is a type of volcanic rock that forms when lava rises into the Earth’s crust but does not erupt at the surface. El Capitan and Half Dome, in Yosemite, California, are examples On similar granite boulders that have risen to the surface.
The presence of such a large granitic deposit that you would not expect indicates that there may be other regions on the Moon where granite can be found. Maybe elsewhere in the solar system, too.
The results are reported in the journal nature.