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Most people who know anything about rocks and minerals are aware of granite. It’s a fairly common mineral rock that is commonly found beneath extinct volcanos (as well as, recently, in finer kitchens as countertops). While granite is fairly common on Earth, it in only rarely found elsewhere in the Solar System. For example, only a few grains of granite were found in rocks and sand brought back from the Moon. However, analyzing data from the Chinese Chang’e lunar probes has revealed evidence for an underground granite formation 50 kilometers in diameter on the far side of the Moon. This formation lies under a feature called the Compton-Belkovich Volcanic Complex. The Chang’e data revealed a much higher heat flux from this region than anywhere else on the Moon, by a large margin. Granite incorporates radioactive isotopes within it, such as thorium; the radioactive decay of these isotopes is what causes granite to be warmer than other minerals.
The discovery of a large amount of granite on he Moon is a surprise to scientists. On Earth, the formation of granite requires plate tectonics and water. While there is a very small amount of water on the Moon, there have never been lunar plate tectonics. Plate tectonics require a geologically active body driven by a molten core. While a portion of the Moon’s core is thought to be molten, it’s not sufficiently large or hot to drive the sorts of geological phenomena we observe on Earth credited to tectonic plate activity, that is, earthquakes and volcanism. This raises a big question: if the Moon lacks the sort of environment associated with the formation of granite on Earth, then just how did the lunar granite form? The paper proposes a few possibile mechanisms, though they require water being present in amounts that are not found on the present-day Moon.
One thought that occurred to me was that the granite might have been produced here on Earth and then transferred to the Moon during the hypothesized giant impact of the two proto-planetary bodies that eventually formed the Earth-Moon system. However, that impact, if it occurred, would have happened 4.5 billion years ago, and the Compton-Belkovich Volcanic Complex only dates to 3.5 billion years ago. So much for that idea.
Finally, the researchers point out that this study is the first to use passive microwave radiometry to a produce thermal map for a celestial body that is not the Earth. This method can be applied to lost of other satellites and a few planets elsewhere in the Solar System.
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From annieli's diary, wherein complaints are lodged by Republicans about woke poetry-writing in the Navy: a fine example of maritime poetry is spontaneously composed in a thread started by McGovern78 and continued by Ex Nox Stellarum and dnr3114.
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