2019-04-17 - Kinetic Energy in Seven Eves

I've been reading Seven Eves by Neal Stephenson, and in it there is an event referred to as the "White Sky" in which a significant portion of the Moon will fall to Earth. The event is predicted and named within the first 5% of the book, and talked about on the cover jacket, so there is no spoiler here.

The reason for this event is that the Moon has (for some unknown reason) broken into several very large pieces. These pieces are not flying apart from eachother in some huge explosion, and so they remain gravitationally bound, which means that they will bash into each other and break up more. This is an exponential process that will eventually pulverize most of the moon into small chunks of rock.

Most of the pieces remain in orbit, and even after bashing into each other, only some will end up heading in towards the Earth. But, since the process is an exponential one, the vast majority of rock sent towards Earth will end up being from near the end of this process, and hence will be fairly small, less than a few meters in size. Also, they will all strike within a fairly small window that's a few days to a month long.

So, lets calculate this... The total kinetic energy of the Moon is about 7.35 * 10^28 joules. Let's say that 1% (most of the moon won't fall down, and not all of it will fall down in the small window) of this kinetic energy ends up being deposited within the small window. It takes 4.186 joules of energy to heat one gram of water one degree C. That's enough energy to heat 1.755 * 10^23 kilograms of water by 100 degree C. There's approximately 1.4 * 10^21 kg of water in the oceans.

That's easily enough energy to boil all of the oceans. Even if it takes a month, there is no way enough energy is going to be radiated away to keep that from happening.

It's kind of awe inspiring to realize just how much energy is locked up there. The extermination of almost all life on Earth would be extremely sad. But, also awe inspiring at the same time. The name given to the event by the people in the book is quite apt.