Senior Scientist at PSI and primary author of the research paper "Remote Detection of a Lunar Granitic Batholith at Compton-Belkovich," published in Nature, Matthew Siegler, explains the historical progression of lunar understanding: "Before the 1950s, most scientists believed the Moon's craters resulted from volcanic activity. However, subsequent studies in conjunction with the Apollo missions revealed that these craters were predominantly the product of impact events."

The Moon does have a history of volcanic activity, with flood basalts, or thin flowing lavas, enveloping about 16% of its surface. Yet, the presence of thicker, silicic lavas that could form a distinct volcano is relatively scarce, according to Siegler.

The Chinese Chang'E 1 and 2 lunar orbiters were key in the discovery. Siegler noted, "Using a microwave wavelength instrument, we have been able to map temperatures below the Moon's surface. We found that one of the suspected volcanoes, known as Compton-Belkovich, was incredibly radiant at microwave wavelengths."

These findings hint at the existence of a heat source beneath the volcano, not on its surface, as infrared technology might suggest. This discovery implies that Compton-Belkovich hides a larger heat source beneath its visible structure.

Given the last known eruption of this volcano occurred approximately 3.5 billion years ago, the heat detected is unlikely to originate from molten lava. Rather, scientists believe it stems from the radioactive elements present within the now solidified rock. They concluded that only granite would contain sufficient quantities of these radioactive elements.

The evidence, collated using this groundbreaking microwave instrument, suggests that this lunar volcano was once fueled by a larger granite magma chamber beneath it, representing the most Earth-like volcanism found on the Moon to date.

Granitic batholiths are massive bodies, exceeding 20 kilometers, of once subsurface lava that never erupted. These batholiths, akin to those beneath Earth's volcanic chains such as the Andes or the Cascade mountain ranges, essentially serve as the plumbing system for these volcanoes. The cooling of these systems leads to the formation of granite, a type of rock that is essentially cooled-off lava that failed to reach the surface. This type of rock is nearly absent outside of Earth in the Solar System.

The international collaboration was a vital aspect of the project, with PSI's Jianqing Fang, a co-lead author, and PSI-funded students Katelyn Lehman and Mackenzie White, serving as co-authors. The project was funded by a grant to PSI from NASA's Lunar Data Analysis program and Lunar Reconnaissance Orbiter mission.

Siegler praised the collaborative efforts, "It was a neat project in that China made their data public - as does NASA- and we were able to work with this unique data set to figure out something really interesting about the Moon." He also credited Jianqing's ability to navigate the data and existing literature on the topic, as a testament to the power of scientific and political cooperation.

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