Science of Anime: Destroying the Moon

Another one from Dragon Ball. Goku’s transformation into a Great Ape is triggered by the light of the full moon, so “Jackie Chun’s” method of changing him back is to use his Kamehameha to blow up the moon. For how much of a task it is to do that, see “Destroying a planet”. This post is going to be about what would happen to Earth if the moon was destroyed.

In Dragon Ball, it seems like it has almost no effect, with the most serious consequence being the fantasy-based one that Manwolf can’t turn into a man anymore. (Manwolf should not be confused with a wolfman.) But there are other consequences that don’t come up. (Including the fact that Roshi “Jackie” killed that rabbit boss guy that Goku stranded on the moon in an earlier episode.)

First of all, if the moon exploded, pieces of it would hit the Earth at high speed. Depending on the size of the pieces, this could kill everyone near land impacts, cause giant tsunamis if they hit in the ocean, and fill the air with so much dust that the sun isn’t visible for years. If the Moon were reduced to very small pieces, we’d witness the biggest meteor shower in history and the weather would probably still be significantly effected.

Okay, but besides that. The moon did blow up in Dragon Ball (and then a second time in Dragon Ball Z), but it was able to be restored by just magically making it appear, so let’s suppose it just magically disappeared.

It would still be kind of a disaster.

The biggest issue is the tides; the moon is the primary cause of them. The way it works is that the strength of gravity decreases with distance (specifically, it falls off equal to the square of the distance), so the moon’s gravity pulls more strongly on the near side of the Earth than the far side. The solid part of the earth is stretched a little, but of course the ocean’s shape is changed much more easily changed. So there are two bulges of water, one on the side facing the moon and one on the side opposite it. If the moon and its gravity suddenly vanished, the phrase “tidal wave” would actually be correct for once as those bulges collapsed.

After that, a lot of plants and animals living on coasts, that depend on the tides, would suffer, and beaches would shrink, but since Earth would still have some tides due to the sun, I’m not sure it would lead to a mass extinction.

Additionally, the gradual slowing of the Earth’s rotation that is being caused by the moon’s tidal forces would cease, but that wouldn’t really be noticeable to anyone except scientists making precise measurements. (However, if the Earth had never had a moon, the day would be far shorter, and it’s possible that life would have been slower to spread to the land.)

It would also be bad news for people who like moonlit walks, which is something that the tournament announcer in Dragon Ball did mention.

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