Roland Emmerich’s latest effort to find new and cataclysmic ways to mount an attack on Earth is finally here. And it answers to the name of Moonfall. Having explored on the big screen, via big bangs (small ‘b’), bigger effects, and the biggest of liberties taken with science, the likes of a new Ice Age in The Day After Tomorrow, the Earth’s core heating up in 2012, and aliens attacking in Independence Day, director Emmerich now threatens our existence in Moonfall with the prospect of the moon… er… falling into the planet.
Coming hot on the comet tail of Adam McKay’s satire about a planet-killing body hurtling towards Earth, Don’t Look Up, and the very real fear of imminent climate change poised to irreversibly destabilise the conditions under which we live and, indeed, destroy all life on this rock, Emmerich’s Moonfall taps into real-life concerns – and then cranks them up to 11 beyond the realms of plausibility in a big-screen spectacle. But wait, is what happens in the movie that far-fetched?
Moonfall’s Insane Premise
If you haven’t seen Moonfall yet, look away now as we are about to majorly spoil things with a summary of the plot.
When the moon’s orbit is found to be getting closer to Earth, it sets off tidal waves, upsets gravity, and interferes with the atmosphere. The moon is discovered to be an artificial megastructure, rather than an organic body, that is hollow inside, with the Apollo 11 mission having discovered its abnormalities and kept it secret. It transpires that a hostile artificially intelligent nano swarm has been drawing energy from the megastructure’s energy source – a captured white dwarf at its centre – which is the cause of the moon’s destabilization.
A small team made up of John Bradley’s conspiracy theorist, Halle Berry’s NASA executive, and Patrick Wilson’s disgraced former astronaut, heads inside the moon with the intention of destroying the nano swarm using an EMP device. While there, they discover that the megastructure was built by humanity’s technologically advanced ancestors as a way of conserving life and repopulating. This, after their AI became sentient and intent on destroying them. The trio learns that the moon – and other megastructures like it – was constructed and seeded with their ancestors’ genetic code as a kind of ark designed to seek out new hospitable parts of the universe in which to rebuild life. The nano swarm, we are told, is programmed to seek out organic matter in electronic environments, its primary purpose to seek out humanity and destroy it.
Sounds kind of far-fetched, right? Well, we spoke to an actual astrophysicist – Professor Kathy Romer from the UK’s University of Sussex – in an attempt to cut the wheat from the chaff and dive into the science of the movie, and the possibility of any of the events playing out like they do on screen in real life.
Could the Moon Leave Its Orbit?
First things first, could the moon actually leave its orbit? If it could, how could that happen; and would it play out the way it does in the film if it did?
“The only way [in real life] is if there’s another large object — or objects; you could do it with multiple — to disrupt its orbit,” says Professor Romer. “Because although the moon is attracted to the Earth by a strong gravitational force, it can’t fall into the Earth because it’s got angular momentum. It’s the same reason all the planets go around the sun, and all the moons go around their respective planets, it’s because you can’t fall in due to the angular momentum.
“The only way to change the angular momentum is to apply a force that’s in basically the opposite direction of travel. To get rid of the angular momentum, which essentially would make the moon into a pebble that you’d thrown up into the sky, you’d have to have something that’s the same mass as the moon traveling at the same speed in the exact opposite direction. Or you can have something that is much more massive, not even traveling in the same direction and not traveling as fast.”
A Large Body
Okay, so maybe something like the comet from Don’t Look Up? Well, maybe not because that was much smaller than the moon.
“As for where you’re going to get this thing from… well, there are large bodies in space, there are large asteroids and things like that,” says Romer. “But they’re all piddly compared to the size of the moon. You could have something less massive, but traveling much faster. However, the solar system’s been around for about 5 billion years, and all of those sort of erratically flying objects have been cleared out. They basically get cleared out by the gravitational pull of either the sun or of Jupiter. So, there isn’t anything natural out there that could do this.”
Perhaps a huge alien ship could do it. The ships in Independence Day were pretty big. Although Emmerich didn’t introduce these guys into the plot of Moonfall, thereby electing not to set up a shared universe (and some of us might be a bit sore about that), surely a big alien ship colliding with the moon could theoretically knock it out of orbit?
“Well, the alien ship to be the same as the mass of the moon is just bonkers,” says Romer. As bonkers as the actual plot of Moonfall, you might say. “You could have a naked black hole. Now, there are models where Dark Matter is actually made up of black holes that were generated very early in the universe, what are called primordial black holes, and they could have any mass; they could be tiny. They can’t be more massive than the mass of the Sun for astrophysical reasons. If one of those happened to come — and they would have been floating around in space since the Big Bang — you could imagine that one of them might be on a trajectory that took it inside the solar system and then come close enough to the moon to knock the moon off course.”
Could the Moon be Hollow?
As we know now that the film is out, it’s none of these things that actually causes the moon’s shift in orbit in Moonfall but it’s good to know that there’s a slim chance it could happen in real life and what could cause it. It’s good to be prepared. So the next question is, could the moon actually be hollow?
Says Romer, “Well, there are lots of seismic detectors; there are mirrors on the moon; there’s laser pointing. So, if you shake a solid body, you get wobbles. It’s a bit like having seismic meters for volcanoes and eruptions. So we know what the properties of the interior of the moon are, and it’s not hollow. That’s just nonsense. We know its orbit very well; we know its distance [from the Earth] very well because we have these lasers. You fire a laser at the moon and it comes back and we know the speed of light so we know exactly how far away it is. And therefore we know how long it takes to orbit the Earth. So, it’s very simple physics to figure out how massive the moon is. Most of the density of the moon is in the middle, like most of the Earth’s mass is in the middle. The only way for [a hollow moon] to work is if you could mimic extra mass. It’s basically all just mind-boggling nonsense. No, it can’t be hollow.”
Roche Lobes
So let’s move back to the idea that the moon is on a collision course for Earth as it travels out of its orbit. The effect on Earth caused by its closeness to the planet results in tidal waves, a strong gravitational pull, and the dissipation of the atmosphere. There’s also mention of gravity waves. How accurate are these knock-on effects?
“I mean, a tidal wave fine,” says Romer. “But gravity wave is a stretching of time and space. It’s not a great big wave. And the sort of floating up into the sky of stuff is not really plausible, because the gravity from the Earth is still stronger than the gravity from the moon, if the moon is the mass that we think it is now. But of course, if it was the mass of the sun, then yes, of course, everything would have flown off. One thing they did do well was talking about Roche lobes, which is about the fact that once two objects get close enough, then they’ll start breaking each other apart. Now, that was a tick.”
Nice one, Emmerich. Wait, could this thing – this megastructure — with its white dwarf inside, actually be the mass of the sun in real life?
“There are just so many things wrong with [the idea of a white dwarf inside the moon],” says Romer. “Now, a white dwarf is a very compact object. But, you know — people have heard of neutron stars — neutron stars are ultra-compact objects, they’re a few tens of kilometres across. White dwarfs are actually about the size of a normal star.”
Our sun is considered an average star at around 1.4 million kilometres across. Our moon, meanwhile, is about a third the size of the Earth, at around 3,500km in diameter.
White Dwarf Science
“White dwarfs only get smaller if they’re heavier, because of the way that they’re contracting under their own gravity. So the heavier they are, the smaller they are. So, I did a bit of back-of-the-envelope calculation, and the only way to get one small enough to fit inside the radius of the moon, it would have to be the mass of the Sun. So then you’ve got something the mass of the Sun orbiting the Earth. Well, then the Earth would be orbiting the moon because obviously it’s the heaviest thing nearby. There was this sort of hint in the film that somehow they were able to mask the fact that it had a white dwarf in the centre by some massive gyroscope. Well, you can’t, the mass is there.
“Gravitational attraction between the two bodies exists, there’s no way to fake it unless… the benign AI was pumping energy in the opposite direction to push it away from the Earth. So the Earth didn’t feel the full gravitational force. But then you would know because you could see all of this force coming towards you.”
But there’s another issue with the white dwarf and what happens in the movie.
“White dwarfs are really quite unpleasant objects,” explains Romer. “They’re extremely hot. They’re formed after the death of a star. And they cool down really slowly — to the point that there are no stars in the universe that have cooled down to the point they’ve lost all their energy. And a lot of this energy comes off as gamma rays and X-rays. That would mean that you’ve got this enormous source of gamma rays and X-rays really close to the Earth.”
Ah. This is a problem.
“Now, of course, they’ve encased the megastructure in rock,” continues Romer. “As a plot device, I just couldn’t get my head around this.” Romer suggests that perhaps they had to encase it in the rock to stop the toxic radiation from the white dwarf killing off all life on Earth – though points out that they wouldn’t necessarily had to have used rock, they had other materials at their disposal that could have been more effective.
“What would happen is that the emission from this star would be evaporating the rock from the inside. And certainly, once the astronauts got into that place, they basically would just die from radiation poisoning. As soon as they got to the point that they were that close to the white dwarf, they would be dead.”
Oh dear.
Gravity Schmavity
Let’s return to this idea that the atmosphere of the Earth is affected. What’s going on there? Professor Romer has an issue with why the atmosphere came back at all at the end of the movie.
“There’s no reason for the atmosphere to come back,” she laments. “And why did they all go to Aspen? If you’re going to go somewhere safe, don’t go into the mountains…”.
She also has an issue with the way gravity behaved on Earth.
“They had to wait for the moon to rise for the gravity to kick in. Well, that’s nonsense,” she says. “Gravity doesn’t care. It only cares about distance. And in fact, if the moon was on the other side of the Earth, then things would stick more to the Earth because there’s more gravity.”
Anything else that was okay, physics-wise?
“They were all right on the precessing of the orbit,” says Romer. “So they talked about the fact that the moon had gone out of orbit, and it had gone into an elliptical orbit, and it was going to have to go around a few times before it made an impact. That was okay. It’s just the precession, that sort of decay of the orbit, would have taken… I haven’t done a calculation, but my sense is millions of years.”
So there we have it. The science of Moonfall is pretty much complete and utter nonsense.
Moonfall is out now.
Professor Kathy Romer is originally from Tyneside. Kathy was awarded her BSc in Physics with Astrophysics from the University of Manchester in 1990 and her PhD in Astrophysics from the University of Edinburgh in 1995. She then moved to the USA and was a postdoctoral researcher at Northwestern University and at Carnegie Mellon University (CMU). After a short time as a research professor at CMU, she secured a tenure track position there. She moved back to the UK in 2004 to take up a lectureship at the University of Sussex. She is still at Sussex and is now Professor of Astrophysics and the Director of Student Experience for the School of Mathematical and Physical Sciences. Kathy is a world expert in the discovery and exploitation of X-ray clusters of galaxies. She is principal investigator of the XMM Cluster Survey collaboration and is senior member of the Dark Energy Survey collaboration.
For more Moonfall-related goodness, check out our round-up of Roland Emmerich’s best ways of destroying the Earth in the article below.