What would happen if the moon suddenly blew up
The moon is no small object, something that the solar eclipse of August 21 illustrates in stunning detail.
And though it's implausible, the destruction of that object would be devastating.
It's no spoiler to say that in Neal Stephenson's 2015 novel "Seveneves" - a fictional exploration of this very idea - the moon is destroyed.
That's because the opening line reads: "The moon blew up with no warning and with no apparent reason."
We don't how the moon would suddenly explode in the real world - it's unlikely. But the way Stephenson describes the events that would happen next carries a surprising amount of truth.
Business Insider spoke to several physicists who have considered this nightmare scenario. What they had to say did not bring us comfort.
Warning: Mild spoilers follow that for the situation that sets up Stephenson's science fiction novel "Seveneves."
What if the moon blew up?
"Seveneves" falls into what's sometimes known as the "hard sci-fi" category. The classification can be broadly interpreted, but it tends to include stories that strive to keep things within the realm of scientific plausibility.
That plausibility gives authors a lot to work with: In our world we can already rewrite the genetic code for life, are planning missions to land on Mars, and even working on sending fleets of tiny spacecraft to investigate star systems that are light-years away.
So what would happen if the moon were to be mysteriously blown up - perhaps the hardest thing to explain in the book?
In short, a fiery rain of moon debris that could last for thousands of years, wiping out almost all life on the surface of Earth.
But here's how physicists say that could play out.
The explosion
The cause of the moon's destruction matters a great deal, since it could tell you how fast the pieces of the moon are moving, how big they are, and which direction they're headed.
But as that opening line of "Seveneves" explains, there's no identifiable agent - just a sudden breakup of our natural satellite into seven major chunks, plus countless other minor fragments that gravity would hold together in roughly the same region of the moon formerly known as Luna.
It would be difficult to actually blow up the moon, to say the least. Depending on the way that the force needed was applied, you could expect wildly different results.
Still, there's at least one possible explanation for a theoretical moon explosion, according to Daniel Freeman, a graduate student in physics at UC Berkeley who wrote about "Seveneves" for the Berkeley Science Review.
Freeman told Tech Insider that a "rogue planet," which is a world "not gravitationally bound to any particular solar systems - planets that essentially are just hurtling through space," could collide with and annihilate the moon. (We'll take this moment to note that rogue planets may outnumber stars 100,000 to 1.)
However the moon dies, its breakup would set loose massive fragments of space rock and iron near Earth. And it's what happens next that's terrifying.
In the book, the moon breaks up into seven major and countless minor fragments. There's a brief and global sigh of relief as it seems those major moon fragments are spinning and moving, but generally being held in the region of what was formerly known as our moon.
However, one massive fragment (referred to as Scoop) smashes into another (Kidney Bean), splitting it into smaller parts. Along with scientists around the world, one of the story's protagonists - a science-popularizing astrophysicist named Dubois Jerome Xavier Harris, Ph.D., or "Doc Dubois" - realizes the significance of this collision.
The White Sky
Dubois realizes that as each large moon fragment crashes into another, more and more moon fragments will be created, increasing the probabilities of further collisions.
This runaway scenario is what real-world physicists call the Kessler effect or Kessler syndrome. It's the reason some scientists fear the buildup of space junk in orbit around Earth could become so severe that it eventually becomes impossible to launch satellites or rockets through the chaos, wiping out satellites and cutting us off from the universe beyond our planet.
Dubois calculates that approximately two years after the moon's breakup, the skies will become inaccessible, with the material that comprised the former moon becoming a massive cloud or ring around the planet. He calls this the "white sky."
Planetary physicist Erik Asphaug, who studies giant impacts with moons and planets, told Tech Insider that - depending on the conditions of the moon's initial breakup - it's indeed possible that "the Moon's debris would form a torus [like a doughnut-shaped ring] around the Earth, and large chunks could be forced inwards by tides and dragged gravitationally by resonances with torus material."
In other words, some debris would impact and parts would actually build up in the skies in a ring around our world.
Freeman used computers to simulate how plausible Stephenson's scenario might be. He said the white sky might occur much faster than Stephenson suggests, but notes the author's scenario is definitely "theoretically plausible."
After that things come crashing down.
The Hard Rain
Two years of buildup of moon debris, Stephenson's tale gets very dark.
"It is going to be a meteorite bombardment such as the Earth has not seen since the primordial age, when the solar system was formed," the book's character Dubois explains. And that constant fiery bombardment from the sky is going to last somewhere between 5,000 and 10,000 years, laying waste to all land and generating enough heat to potentially evaporate oceans.
Ouch. And, scarily enough, this is all feasible.
Freeman's simulation of the moon's explosion is below, with Earth represented as a big blue dot and the moon as smaller multi-color dots. He said to take it with a large grain of salt, since it's a rough approximation, but it's nonetheless discomforting:
Not all the moon needs to hit the Earth to cause a rain of destruction. But enough of it would strike that Freeman says he's "not at all surprised by a 10,000-year timescale for the moonchunk barrage."
Asphaug's response agreed, though he didn't estimate the timescale.
"I think the end game would be some initial [random] impacts on the Earth, by stuff that just happened to be heading the right (or wrong) way," Asphaug wrote, "followed by massive bands of impacts for some longer time, perhaps by a flattened ring with impacts concentrated equatorially, but maybe not flattened in which case impacts on Earth would be everywhere."
That massive band of impacts could be the hard rain described by the novel.
The only glimmer of hope in Stephenson's novel comes from a plan to try to create space colonies where humanity can survive for thousands of years.
The idea that we have to colonize space might sound crazy, but many think it could be essential.
Real-world proponents of space colonization, including Elon Musk and Stephen Hawking, argue that we need to create ways for humans to live off this planet in case we somehow make it uninhabitable for life. And projects like the NASA- and DARPA-funded 100-Year Starship program are trying to figure out how to build a spaceship that a group of people could live on for centuries during an interstellar voyage.
So while "Seveneves" may be a grand work of fiction, the physics involved - and the implications - don't stray far from the truth.
And in case anyone was considering blowing up the moon just to see if they could, please don't.