Melting down the Moon

Think about it on a full moon day: if the attack in Space Battleship Yamato really happened, the moon would “always be full”!

Zordar: “This is my power!”
Commander: “The moon…we have no choice but to surrender!!”
Kodai: “While we’re on Jupiter…!?”

Published on, February 6, 2023. See the original article here.

Illustration by Yutaka Kondo

Hello, I am Rikao Yanagita of the Dream-Science Laboratory. I enjoy discussing manga, anime, tokusatsu programs, etc. from the viewpoint of fantasy science. Now, here is this research report…

On February 6, there will be a full moon. Among the full moons in 2023, it will be the farthest full moon from Earth and will appear the smallest. Compared to the largest full moon (supermoon on August 31), the apparent diameter is 12% smaller. It is also called a micro moon.

When I look at the moon with such thoughts in my mind, I remember that it has been the victim of many terrible things in manga and anime. Assassination Classroom started with an incident in which 70% of the moon was vaporized. In Symphogear, there was a person who tried to destroy the moon and drop debris on Earth. In Dragonball, the moon was made to disappear because Goku and Gohan started to go berserk due to the full moon!

Because it is a celestial body close to us, the moon has caused us a lot of trouble. Among them, the one I can’t forget is from the 1970s anime Yamato 2. This is the second in the series that began on TV in 1974 and became a big hit when it was made into a movie in 1977 (a compilation of all 26 TV episodes).

A new invader, the Comet Empire, bombards the moon to show its power to the people of Earth, and melts it into mush. This is a big nuisance for the moon, but from a fantasy science point of view, it is a bit disturbing. How powerful does an attack have to be to melt the moon?

What is the temperature of the moon?

The invader at this time was the Gatlantis Empire led by Emperor Zordar. They overran solar systems with their mobile fortress, the Comet Empire, and finally approached the Earth. He said, “Surrender unconditionally or we will immediately obliterate your planet.” When the people of Earth were upset, Zordar said, “Let us show you just how powerful we are.”

Beams of light were fired from the Comet Empire toward the moon and explosions occurred on the surface until the whole thing was engulfed in a fireball. Eventually, it turned orange…! Regarding this astonishing situation, a presidential official said, “The entire area (of the moon) is now incandescent under the concentrated fire of the enemy fortress.”

When an object is heated and its temperature increases, the color changes from dark red to bright red → orange → yellow → white → blue-white. In the story, the color appeared to be orange, but from the fact that he says “incandescent,” it may be that the object was heated further after that.

The basalt covering the moon melts at 1100 degrees Celsius, and becomes incandescent at 1300 degrees Celsius or higher, so the moon must have reached that temperature. The energy required for this depends on the depth of the melting. Observing this scene in Yamato 2, it is clear that the Comet Empire was irradiating the moon from only one direction, but it was melted to the opposite side. This means that the entire moon was melted down! This must have taken a lot of energy.

The surface of the moon is 110 degrees during the daytime and -170 degrees during the nighttime. At a depth of more than 1 meter, the temperature is -30 degrees Celsius, the same during the day and night.

Let us assume that the temperature of the Moon is -30 degrees Celsius. The Moon weighs 7,400 kilotons (Kyo is 10,000 times a trillion), and the energy required to raise the temperature of such a large rock from -30°C to 1300°C, or 1330°C, is 9 J. (a trillion times greater than Kyo). If written in numbers, it is 90000000000000000000000000000J!

The moon is always full!

How much energy is this? If we compare, for example, the hydrogen bomb test at Bikini Atoll, the energy released by the Comet Empire is equivalent to 1.43 trillion hydrogen bombs used in the test. The nuclear weapons on the earth today are said to be equivalent to 200 Bikini H-bombs. The Comet Empire unleashed a beam 7.2 billion times more powerful.

If such a beam were to be fired at the Earth with a population of 8 billion human beings, each one of us would suffer the equivalent of 180 Bikini H-bombs. That’s insane!

But the story does not end there. If heated to 1,300 degrees Celsius, the moon would begin to glow on its own. The moon changes its shape from crescent moon to half moon to full moon because it reflects the light of the sun. If it were to shine with its own light, it would always be a full moon!

The brightness of the light reaching the earth from a 1300-degree full moon would be 520 lux. This is brighter than 300-500 lux, which is just right for reading and studying. I could save money on my electricity bill, but this would not be something to be happy about.

There would be no night, so animals and plants would lose their rhythm of life. The ecosystem would be ruined. However, it would actually be worse for the members of the Comet Empire. The scene depicts them as being only about 1,000 km away from the moon. At this close range, the surface temperature would soar to 980 degrees Celsius! What aliens could withstand this?

This sort of showmanship also means that if you overdo it, you’ll be the one who gets hurt. I hope Zordar and others will take this as a good lesson.

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