Spoilers... but not many.
When reading science fiction, there is always the need to suspend your belief. For Hard science fiction the need to disbelieve is much less.
After I sent my copy of Seveneves to my brother, we had a chance to discuss the book a little bit. I agree with most of his critique; the one thing that totally annoyed him, which I ignored, was the initial cataclysmic event that starts the whole story.
If some high energy event occurred, whether a collision from some object travelling at high velocity or planted alien bomb, one would expect some major changes. In the story, everyone sort of ignores the Agent, the name for the thing that blows up the moon, and focuses on survival. As my brother pointed out, surely someone who wasn’t part of the exodus or supporting the exodus would have the skills, equipment and curiosity to investigate what happened. What if more of these things were headed at the earth, like a near light speed meteor shower? So it was all glossed over and there really isn’t enough information to figure out why the moon partially disintegrates and turns into the white rain that cooks the earth.
How do we model this? Experience and tons of slow motion Youtube videos give us some context when something travelling at a high rate temporarily occupies the same point in space as a watermelon, water balloon, etc. But regolith and lava? And how does it scale? Whatever shatters the moon transfers enough energy to liquefy some of it and distribute the rest. But the book points out two facts on the first page: “…a blur flourishing in the vicinity of the Reiner Gamma formation.” And the moon fragments were described as “…objects still gravitationally bound.”
The angle of impact matters because if it passes tangentially relative to the lunar orbit, the orbital velocity will increase or decrease depending on the vector. Perpendicularly the velocity vector will perturb the orbit so the moon oscillates between the poles as it orbited the earth. If an object impacted the moon and exited near Reiner Gamma, I'm (get a towel because I use no hard science here, all spit balling) seems like it would accelerate the moon out of orbit. If it was a planted bomb, then the eye witness account suggests it would decelerated the moon. Given the enormous energy involved, one would expect the chunks not transferring to other orbital altitudes would keep intersecting the original center of gravity, grinding away until entropy and friction turns everything into a dusty orbital ring.
So two ways to move a significant chunk of the moon into an orbit that would degrade in 4 to 5 years. The first is to decelerate the moon with tons of energy in a sustained burn. The other way is to use a shaped charge to blow a chunk into a slower orbit (I chose 1,000 km so atmospheric drag could do some of the work). This would require (spit balling plus some rough numbers in an orbital calculator) gives us about 800 m/s delta-v. The energy to accelerate 1 kg to that speed is 320000 Joules, which is roughly 1/4000 a gallon of gasoline. Dynamite is has a density of 5.0 MJ/kg. So a 100% efficient shaped charge of a kg of dynamite could move 15.6 kg into a decaying orbit.
How big a chunk do we need? One chunk that keeps getting cited is Apophis at 40 billion kg, a requiring a mere 2.5 million kg of dynamite. According to one Wikipedia article, the entire nuclear arsenal is currently equivalent to about 6.3 trillion kg of dynamite which should be plenty. However if some alien wanted to kill us there would be cheaper and easier ways to do this.
So if the Agent was a high energy beam or collision, I'm not sure the white rain scenario makes sense. A bomb of some sort planted inside the moon might be able to create the desired effect, but again, doesn't really add up. If some alien intelligence really wanted to kill us in such a bizarrely dramatic, complicated and inefficient way, their motivation wouldn't be to kill us all but cull the population and force us to emigrate to space. And the only possible hint at that is towards the end of the book, there's mention of a higher "Purpose", a movement or goal being guided by a nameless, powerful and wealthy cabal.
There's one way this makes sense, but I really have to reach deep inside myself to my inner uber nerd: The Star Trek Hypothesis. To create that much energy one would need to convert less than 1/4 kg of mass into pure energy. So Spock and Kirk sling shot around the sun to go back in time and beam down to the moon near Reiner Gamma to prevent the Agent from ever occurring. Unfortunately due to a transporter malfunction they beam inside the moon and some of their atoms (estimated to be about 1/4 kg using the R.O.M.A* method) fuse with the moon creating a massive explosion. This changes the history of the Federation, pushing it out 5,000 years farther, but hey, we already know the ST universe is a multi-verse.
When reading science fiction, there is always the need to suspend your belief. For Hard science fiction the need to disbelieve is much less.
After I sent my copy of Seveneves to my brother, we had a chance to discuss the book a little bit. I agree with most of his critique; the one thing that totally annoyed him, which I ignored, was the initial cataclysmic event that starts the whole story.
If some high energy event occurred, whether a collision from some object travelling at high velocity or planted alien bomb, one would expect some major changes. In the story, everyone sort of ignores the Agent, the name for the thing that blows up the moon, and focuses on survival. As my brother pointed out, surely someone who wasn’t part of the exodus or supporting the exodus would have the skills, equipment and curiosity to investigate what happened. What if more of these things were headed at the earth, like a near light speed meteor shower? So it was all glossed over and there really isn’t enough information to figure out why the moon partially disintegrates and turns into the white rain that cooks the earth.
How do we model this? Experience and tons of slow motion Youtube videos give us some context when something travelling at a high rate temporarily occupies the same point in space as a watermelon, water balloon, etc. But regolith and lava? And how does it scale? Whatever shatters the moon transfers enough energy to liquefy some of it and distribute the rest. But the book points out two facts on the first page: “…a blur flourishing in the vicinity of the Reiner Gamma formation.” And the moon fragments were described as “…objects still gravitationally bound.”
The angle of impact matters because if it passes tangentially relative to the lunar orbit, the orbital velocity will increase or decrease depending on the vector. Perpendicularly the velocity vector will perturb the orbit so the moon oscillates between the poles as it orbited the earth. If an object impacted the moon and exited near Reiner Gamma, I'm (get a towel because I use no hard science here, all spit balling) seems like it would accelerate the moon out of orbit. If it was a planted bomb, then the eye witness account suggests it would decelerated the moon. Given the enormous energy involved, one would expect the chunks not transferring to other orbital altitudes would keep intersecting the original center of gravity, grinding away until entropy and friction turns everything into a dusty orbital ring.
So two ways to move a significant chunk of the moon into an orbit that would degrade in 4 to 5 years. The first is to decelerate the moon with tons of energy in a sustained burn. The other way is to use a shaped charge to blow a chunk into a slower orbit (I chose 1,000 km so atmospheric drag could do some of the work). This would require (spit balling plus some rough numbers in an orbital calculator) gives us about 800 m/s delta-v. The energy to accelerate 1 kg to that speed is 320000 Joules, which is roughly 1/4000 a gallon of gasoline. Dynamite is has a density of 5.0 MJ/kg. So a 100% efficient shaped charge of a kg of dynamite could move 15.6 kg into a decaying orbit.
How big a chunk do we need? One chunk that keeps getting cited is Apophis at 40 billion kg, a requiring a mere 2.5 million kg of dynamite. According to one Wikipedia article, the entire nuclear arsenal is currently equivalent to about 6.3 trillion kg of dynamite which should be plenty. However if some alien wanted to kill us there would be cheaper and easier ways to do this.
So if the Agent was a high energy beam or collision, I'm not sure the white rain scenario makes sense. A bomb of some sort planted inside the moon might be able to create the desired effect, but again, doesn't really add up. If some alien intelligence really wanted to kill us in such a bizarrely dramatic, complicated and inefficient way, their motivation wouldn't be to kill us all but cull the population and force us to emigrate to space. And the only possible hint at that is towards the end of the book, there's mention of a higher "Purpose", a movement or goal being guided by a nameless, powerful and wealthy cabal.
There's one way this makes sense, but I really have to reach deep inside myself to my inner uber nerd: The Star Trek Hypothesis. To create that much energy one would need to convert less than 1/4 kg of mass into pure energy. So Spock and Kirk sling shot around the sun to go back in time and beam down to the moon near Reiner Gamma to prevent the Agent from ever occurring. Unfortunately due to a transporter malfunction they beam inside the moon and some of their atoms (estimated to be about 1/4 kg using the R.O.M.A* method) fuse with the moon creating a massive explosion. This changes the history of the Federation, pushing it out 5,000 years farther, but hey, we already know the ST universe is a multi-verse.
* R.O.M.A. - Right Outta My Ass