Really! Compared to planets our moon is quite small.
Interesting that they say it still has 'hot spots'.

from
https://www.seattletimes.com/nation-world/scientists-have-found-a-hot-spot-on-the-moons-far-side/
(Go to the citation to see the photos and maps.)

Scientists have found a hot spot on the moon’s far side
July 18, 2023 at 5:05 pm
A small portion of the Compton-Belkovich volcanic complex on the moon.
The upper two-thirds of the scene shows the volcanic complex; the lower
third of the image is outside of the complex. (NASA/GSFC/Arizona State
University via The New York Times)
In an undated image provided by Jolliff et al, 2011, a composite image
shows the presence of thorium in the Compton-Belkovich volcanic complex
made with data from the Lunar Prospector, a space mission launched in
1998. (Jolliff et al, 2011 via The New York Times)

1 of 4 | A small portion of the Compton-Belkovich volcanic complex on
the moon. The upper two-thirds of the scene shows the volcanic complex;
the lower third... More
By KENNETH CHANG
The New York Times
The rocks beneath an ancient volcano on the moon’s far side remain
surprisingly warm, scientists have revealed using data from orbiting
Chinese spacecraft.

They point to a large slab of granite that solidified from magma in the
geological plumbing beneath what is known as the Compton-Belkovich
Volcanic Complex.

“I would say we’re putting the nail in the coffin of this really is a
volcanic feature,” said Matthew Siegler, a scientist at the Planetary
Science Institute, headquartered in Tucson, Arizona, and who led the
research. “But then what’s interesting is, it’s a very Earth-like
volcanic feature.”

The findings, which appeared early this month in the journal Nature,
help explain what happened long ago beneath an odd part of the moon. The
study also highlights the scientific potential of data gathered by
China’s space program, and how researchers in the United States have to
circumvent obstacles to use that data.

For this study, Siegler and his colleagues analyzed data from microwave
instruments on Chang’e-1, launched in 2007, and Chang’e-2, launched in
2010, two early Chinese spacecraft no longer in operation. Because
Congress currently prohibits direct collaboration between NASA and China
and the research was financed by a NASA grant, Siegler could not work
with scientists and engineers who collected the data.

“That was a limitation, that we couldn’t just call up the engineers that
had built the instrument in China and say, ‘Hey, how should we be
interpreting this data?’” he said. “It would be really great if we could
just have been working on this with the Chinese scientists the whole
time. But we’re not allowed to. But, luckily, they made some of their
databases public.”

Siegler was able to tap into the expertise of a Chinese scientist,
Jianqing Feng, whom he had met at a conference. Feng was working on a
lunar exploration project at the Chinese Academy of Sciences.

This image shows the Compton-Belkovich volcanic complex on the moon’s
far side, with the boxed area indicating a large granite zone, which
could not be picked up by topography. (Matthew Siegler/Planetary Science
Institute/Nature via The New York Times)

This image shows the Compton-Belkovich volcanic complex on the moon’s
far side, with the boxed area indicating a large granite zone, which
could not be picked up by topography. (Matthew Siegler/Planetary Science
Institute/Nature... More
“I realized that combining the lunar exploration data from different
countries would deepen our understanding of lunar geology and make
exciting findings,” Feng said in an email. “Therefore, I quit my job in
China, moved to the United States, and joined Planetary Science Institute.”

The Chinese orbiters both had microwave instruments, common on many
Earth-orbiting weather satellites but rare on interplanetary spacecraft.

The data from Chang’e-1 and Chang’e-2 thus provided a different view of
the moon, measuring the flow of heat as far as 15 feet below the surface
— and proved ideal for investigating the oddity of Compton-Belkovich.

Visually, the region looks unremarkable. (It does not even have a name
of its own; the hyphenated designation is derived from two adjoining
impact craters, Compton and Belkovich.) The region has nonetheless
fascinated scientists for a couple of decades.

In the late 1990s, David Lawrence, then a scientist at Los Alamos
National Laboratory, was working on data collected by NASA’s Lunar
Prospector mission and noticed a bright spot of gamma-rays shooting from
this location on the moon’s far side. The energy of the gamma-rays, the
highest energy form of light, corresponded to thorium, a radioactive
element.

“It was one of these oddball places that just stood out like a sore
thumb in terms of the thorium abundance,” said Lawrence, now a planetary
scientist at the Johns Hopkins Applied Physics Laboratory in Maryland.
“I’m a physicist. I’m not an expert in lunar geology. But even as a
physicist, I saw that stand out and said, ‘OK, this is something worth
further study.’”

In an undated image provided by Jolliff et al, 2011, a composite image
shows the presence of thorium in the Compton-Belkovich volcanic complex
made with data from the Lunar Prospector, a space mission launched in
1998. (Jolliff et al, 2011 via The New York Times)

In an undated image provided by Jolliff et al, 2011, a composite image
shows the presence of thorium in the Compton-Belkovich volcanic complex
made with data from the Lunar Prospector, a space... (Jolliff et al,
2011 via The New York Times)More
The next revelations came after the arrival of NASA’s Lunar
Reconnaissance Orbiter in 2009. Brad Jolliff, a professor of earth and
planetary sciences at Washington University of St. Louis, led a team
that examined high-resolution images of Compton-Belkovich.

What they saw “looked suspiciously like a caldera,” Jolliff said
referring to the remnants of a volcano’s rim. “If you consider these
features are billions of years old, they are remarkably well preserved.”

A more recent analysis led by Katherine Shirley, now at the University
of Oxford in England, estimated the age of the volcano at 3.5 billion
years old.

Because the lunar soil acts as a good insulator, dampening the
temperature variations between day and night, the microwave emissions
largely reflect the flow of heat from the moon’s interior. “You only
need to go about two meters below the surface to stop seeing the heat
from the sun,” Siegler said.

At Compton-Belkovich, the heat flow was as high as 180 milliwatts per
square meter, or about 20 times the average for the highlands of the
moon’s far side. That measure corresponds to a temperature of minus 10
degrees Fahrenheit about six feet below the surface, or about 90 degrees
warmer than elsewhere.

“This one stuck out, as it was just glowing hot compared to anywhere
else on the moon,” Siegler said.

To produce that much heat and the thorium gamma-rays, Siegler, Feng and
the other researchers concluded that granite, which contains radioactive
elements like thorium, was the most likely source and that there had to
be a lot of it.

“It seems to nail down more particularly what kind of material is really
underneath,” said Lawrence, who was one of the reviewers of the paper
for Nature.

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“It’s sort of a tip-of-the-iceberg type of thing,” he said of the
original gamma-ray emissions. “What you see at Compton-Belkovich is sort
of a surface expression of something a lot bigger underneath.”

Volcanism is evident elsewhere on the moon. Plains of hardened lava —
the mare, or seas, of basalt — cover vast swaths of the surface, mostly
on the near side. But Compton-Belkovich is different, resembling certain
volcanoes on Earth, like Mount Fuji and Mount St. Helens, that spew more
viscous lava.

A small portion of the Compton-Belkovich volcanic complex on the moon.
The upper two-thirds of the scene shows the volcanic complex; the lower
third of the image is outside of the complex. (NASA/GSFC/Arizona State
University via The New York Times)

A small portion of the Compton-Belkovich volcanic complex on the moon.
The upper two-thirds of the scene shows the volcanic complex; the lower
third of the image is outside of the complex. (NASA/GSFC/Arizona State
University via The New... More
Granite appears to be scarce elsewhere in the solar system. On Earth,
granite forms in volcanic regions where oceanic crust is pushed down
beneath a continent by plate tectonics, the geological forces that are
pushing around pieces of the Earth’s outer crust. Water is also a key
ingredient for granite.