As an astrophysicist and a film critic, I’ve been waiting my whole life for a big-budget adventure film that spans the whole solar system. There are some stunning sequences in Ad Astra, and many of the details about astronaut life and space travel are spot-on. But some of the themes and ideas that drive the plot are based on astronomical misconceptions.
Ad Astra touts itself as having help from NASA, so presumably someone somewhere gave them some advice. Still, there are plenty of ways science advising can go wrong— miscommunication, script conflicts, misconceptions, and outright mistakes. In Ad Astra, those mistakes range from wrong ideas about space travel to inaccuracies about basic astronomy.
In Ad Astra, astronaut Roy McBride (Brad Pitt) is serving on a communications tower that extends above the atmosphere when an explosion from space causes a catastrophe. Space Command informs him that his father, Clifford McBride (Tommy Lee Jones), thought dead for 16 years, may still be alive out at Neptune and may have something to do with the explosion. Roy must travel to the Moon and then Mars to send a message to his father. Along the way he has to do battle with Moon pirates, space monkeys, incompetent astronauts, the secretive Space Command, and his own personal demons.
The core of the Ad Astra story is that there’s a massive push to look for life outside of Earth. Looking for alien life is great, but everyone in this universe takes exceedingly bad approaches.
Looking for life in all the wrong places
The movie: Years ago, Clifford McBride and crew set out on a decades-long journey to Neptune to search for life around other star systems. They say they are going “to the edge of the heliosphere so that the Sun’s magnetic field won’t affect our instruments.”
Reality: This makes no sense at all. The heliosphere is a real thing—it’s the region of influence of the solar wind—but Neptune is hardly the edge of it. We have actually sent probes past that edge: Voyager 1 exited the heliosphere in 2012, and Voyager 2 did the same in 2018. Voyager 2 left Earth in 1977, and took 12 years to travel the 3 billion miles to Neptune. It took another 29 years to travel the additional eight billion miles to leave the heliosphere. So even if it were true that the magnetic field of the Sun affected the future instruments in Ad Astra, venturing out to Neptune is nowhere near leaving the influence of the Sun.
The best way to look for life is to just stay on Earth and look for signals from another civilization or to find other extrasolar planets and analyze their atmospheres. We’re already doing both today. Two groups of astronomers recently announced that they found water vapor in the atmosphere of a “super Earth”—a planet eight times the mass of the Earth (probably a gas giant) around the red M-dwarf star K2-18, which is about 110 lightyears from Earth.
All along the watchtower
The movie: Roy McBride appears to be an astronaut, but then he steps outside to reveal he is on a giant tower extending into space. Then a series of explosions and accidents happen, and our hero goes tumbling to Earth.
First, let me say, bravo! This is a spectacular sequence that subverts your expectations of what an astronaut should be and is a great way to open a movie. Just as portrayed in the film, at that altitude there is not enough atmosphere to provide friction, and when falling, you can go into an uncontrolled spin that can make you black out.
Reality: Joseph Kittinger, the man who held the high altitude parachute record for more than 50 years, had a similar experience. On his first attempt jumping from a high altitude balloon, in 1959, he went into an uncontrolled spin of around 120 revolutions per minute, pulled 20+ g’s, blacked out, and was only saved because his parachute was set to open automatically. The movie does a phenomenal job of illustrating what a fall from that height might be like, and it is an amazing stunt.
Still, there are a few problems with the sequence. First, the stated reason for the space tower is that it helps us to search for life in the universe. What wavelength does it use? If it is an antenna, it would have to be radio, but almost all radio waves penetrate the Earth’s atmosphere, so there’s no need to extend the tower into space. That’s in contrast to gamma rays, x-rays, or infrared light, which can be blocked by the atmosphere so must be studied via satellite. That’s another thing—it is much cheaper to launch a satellite than to build a space tower.
The only use for a big antenna is to sense very long wavelength radio waves. Both U.S. and Russian militaries use Extremely Low Frequency radio waves to communicate with submarines, involving using either Earth itself or its ionosphere as an antenna. But very little information can be sent this way. These techniques are really used to send a command to surface or to send up a signal buoy so that more efficient communications can be used. But low-frequency radio waves would be ridiculously inefficient for alien communication, since you can only send a few characters per minute. If you are old enough to remember how slow 2400 baud modems were, well, this is more like a 0.1 baud modem. Your cell phone can send signals 100 million times faster.
Chain of fools
The movie: Clifford McBride’s ship had a matter-antimatter engine that is malfunctioning out at Neptune, causing energy pulses that kill tens of thousands of people throughout the solar system, including on Mars and Earth. They say it sends out cosmic rays that “grow stronger as they radiate towards Earth.” They also say the faulty engine could cause a “chain reaction” that would destroy all life in the solar system.
Reality: Cosmic rays do not “grow stronger” as they travel. In general, sources of any kinds of particles or radiation decrease in intensity as they radiate away from their source. They fall off in proportion to the distance squared, so in fact they get quite a bit weaker. That means that if these bursts are killing thousands at Earth, they for certain would have wiped out anyone still alive at their source.
As for the type of engine, chemical rockets probably can’t get you to Neptune, but a matter-antimatter drive is the most efficient form of propulsion conceived that seems plausible. The problem is that matter-antimatter annihilation won’t cause a chain reaction. The filmmakers are confusing it with what happens in nuclear reactors. In fission, when you break one atomic nucleus apart, it produces neutrons, which basically act like shrapnel, and break other nuclei apart. That doesn’t happen in matter-antimatter reactions. When matter hits antimatter, both are destroyed, converting matter to energy via E=mc2. But antimatter is rare in the universe—you’d have to manufacture it for the trip. Once it is used up in an annihilation, no more would be created in a chain reaction. The solar system would not be at risk.
Fun fact: a giant matter-antimatter reaction took place at the beginning of the universe. For an unknown reason, there were a billion and one particles of matter for every billion particles of antimatter. Everything but one part in a billion wiped itself out, leaving just the matter we see today. We can tell because the reaction produces photons and we can count the photons relative to the number of atoms in existence today. We also see no bulk quantities of antimatter left in the universe today, though it is produced in certain particle physics interactions. To produce it, you’d need a particle accelerator and a way to store it.
The movie: The Moon is lawless. Roy has to get from the commercial landing center to a military launch facility on the far side by going through an unsafe area where he is attacked by mining pirates in a buggy chase. The pirates shoot energy weapons at people and a buggy flies into a crater.
Reality: This is probably the coolest sequence in the movie, so I’ll give it a lot of leeway. There’s nothing wrong with constructing a universe in which pirates chase you.
Would guns work in the vacuum of space? Actually, you can shoot a regular gun with bullets in space, because gunpowder has its own oxidizer. As for the plasma weapons or whatever they are in the film, we don’t really know how they work, so sure, that’s plausible.
The Moon rovers are very similar to the ones used on Apollo 15, 16, and 17, which you can see in this amazing footage.
The Soviet Union also sent remote-controlled Lunokhod rovers to the Moon in the 1970s, and China has a Yutu rover exploring the far side of the Moon right now. In the movie, the buggy flying into the crater with ludicrous hang time is great. The Moon only has one-sixth the gravity of Earth, so it would stay in the air for a long time.
The movie: The ship going from the Moon to Mars, the Cepheus, gets a distress call from a research ship studying Comet 17P/Holmes. Roy and company stop to help, but when they board the derelict vessel, they are attacked by what appears to be a baboon. Roy fights the primate and finally depressurizes the area it is in, causing it to explode.
Reality: With normal chemical rockets, you can’t just stop and start up again. It will take you a ton of fuel to stop, then a ton more to start again, and because of the rocket equation, you need lots more fuel to accelerate all the extra fuel. Ion engines do allow lighter spacecraft like NASA’s Dawn to stop and go into orbit around an asteroid (Vesta) and then to travel to a different asteroid (Ceres) and orbit it.
After the launch of Cepheus, the first stage holding the big chemical rocket engines fall away. They later say they are switching to “long-range engines,” and indeed, the engine color switches to blue, like in ion engines. They also seem to be providing constant thrust like an ion engine, in contrast to a chemical rocket, which only fires until the fuel runs out.
The problem with ion engines is that they aren’t effective with big payloads—shooting little ionized particles out of the back of a spacecraft isn’t going to move a big ship. Also, the thrust is ridiculously low, equivalent to the weight of a sheet of paper. It would take them weeks to slow down after getting the distress call, so basically they could not stop in time.
And yes, people really do take animals to space to research what they’d do in zero-g. My favorite real space-animals are mice, who quickly adapt and start pushing themselves off to fly from one side of the cage to the other. Then they learn “race-tracking” where they zoom around the sides of the cage generating centrifugal force mimicking gravity. Seriously, watch the video.
Ad Astra’s sequence is actually pretty cool for showing how the monkeys have adapted to zero-g. And for a movie that is paying so much homage to 2001, I’m glad to see the primates finally got to space.
Still, I can’t for the life of me figure out why you’d take a monkey to a comet. It is much cheaper, easier, and safer to do the same research in low Earth orbit.
Also, neither monkeys nor people explode in space. You can survive a minute or two in the vacuum, maybe even three or four. You might puff up a bit—Kittinger, the man who set the skydiving altitude record, had his glove malfunction on one jump, and his hand swelled up to twice its normal size. He recovered fine though.
The movie: Cepheus, the same ship Roy took between the Moon and Mars, is ordered to go to Neptune without him. Roy sneaks on board the ship after swimming through an underground lake.
Reality: It took the Cepheus 19 days to get to Mars from the Moon. But Neptune is between 10 and 60 times the Moon-Mars distance (depending on where each is in its orbit). So it should take between 190 and 1,140 days to get to Neptune, though the film says it only takes 79. Between running the ship faster and the much greater distance, you’d have to take maybe 100 times the fuel you had on the Mars trips, possibly more. It just defies belief that a ship that goes to Mars could all of a sudden go to Neptune.
Also, on any voyage like that, you have to carefully account for how much weight, food, and air you’ll need. If you’ve accounted for three passengers, adding a fourth can doom everyone, since you may not have enough food or fuel to get back. As it happens, everyone other than Roy dies, which solves the problem, but he wouldn’t have known that when he snuck on board. So he is either stupid or he planned on killing someone. Neither fits the character.
Roy swimming through an underground lake is an amazing sequence. We think there really are underground lakes on Mars, but they would not be pleasant to swim in (or pull yourself through with a rope, as Roy does), even in a spacesuit. The one we know about is near freezing, below a mile of ice, and is probably kept liquid by being extremely salty. It may be full of perchlorates, which are toxic.
The movie: After Roy sneaks onto the rocket, some asshole tries to shoot him and hits a canister that may or may not be a fire extinguisher. The outgassing kills the entire crew except Roy, because he’s wearing a spacesuit.
Reality: Only an idiot would shoot a gun on a vessel where a hole would cause depressurization and kill everyone. You may ask why he’d have a gun in the first place, but no joke, Russian astronauts really do pack heat on Soyuz capsules. These are there in case you happen to land in Siberia and are attacked by wolves or bears. But since there’s a Soyuz always docked to the International Space Station, that means there’s always a gun in space.
It isn’t clear if the canister that gets hit is a fire extinguisher, but it is about the size of one. On Earth, there are lots of kinds of fire extinguishers designed for different kinds of fires. One of the most common fire extinguishers shoots carbon dioxide, which displaces oxygen since it is heavier than air. Is the extinguisher in the film supposed to be carbon dioxide? It seems that you would need more than what’s in the container to kill everyone and it would take longer, but who knows? In reality, people already realized this danger on the ISS, so they developed a water mist fire extinguisher.
There have been fires in space, notably a 1997 fire aboard Mir. A lithium perchlorate canister burned, and since it was designed to produce oxygen in the first place, it was nearly impossible to put out. The astronauts almost died and lost the station. It resulted in the only photo of a celebratory drunken astronaut party, which only came to light after a Freedom of Information Act request.
Don’t go there
The movie: After passing Saturn, a spaceship passes a space telescope.
Reality: One of the biggest misconceptions in astronomy is that people think the Hubble Space Telescope actually goes to the places it photographs. It doesn’t—it just orbits the Earth, only about 340 miles up, and images things that are extremely far away. We put it in space to get it above the Earth’s atmosphere. I can see how this misconception arises, since we do send probes to the planets in the solar system. But traveling through the solar system doesn’t get you any closer to the vast majority of the things Hubble is photographing, considering the light-year distances involved. That would be like crossing the room to get closer to the Moon.
Jumping Jack Flash Gordon
The movie: After Roy reaches Neptune, he’s in the wrong orbit, and he takes the spaceship equivalent of a dinghy to his dad’s ship. It fails to dock properly, so he just lets it float away. Then, to get back, he stands on what looks like a spinning radar, uses a panel to deflect the ring debris of Neptune, and lands back at his ship.
Reality: It makes no sense that having a ship that could get you all the way to Neptune and slow down could not get you in the right orbit or adjust if you’re in the wrong one. Roy claims this is because of ring debris, but that’s nonsense. We have robotic spaceships now that have navigated the rings of Saturn, which are much more extensive.
It takes a lot of energy to change orbits. Just jumping off a spinning thing won’t do it. Plus, just the innermost ring of Neptune is more than 1,000 miles wide, and there are at least five main rings.
Also, ring particles in orbit around Neptune are moving at ludicrous speeds. Even if you are co-moving with some of them, that can’t be true for all of them, since the inner ones will be moving faster. The relative velocities could be hundreds of feet per second, so it is almost like getting shot with bullets. A piece of metal won’t help you.
The Slim Pickens Express
The movie: To get back home, Roy decides to ride the “shock wave” of the nuclear bomb to propel him from Neptune to Earth.
Reality: The U.S. really did think through using nuclear bombs as spacecraft propulsion in the 1950s in Project Orion. But (and it is a big but), that would have depended on using specially shaped bombs and a special damping mass that provides something to push against, can protect the crew, and damp out the effects of instantaneous acceleration.
We’re used to seeing shock waves in nuclear explosions, but these arise because the explosion sends a shock (pressure discontinuity) through the air. With no air in space, you just get whatever shock you can from the air in the exploding ship (not much) and a ton of shrapnel. That would just fly right through the ship you are supposed to accelerate, killing everyone.
Ever heard of a phrase called “nuking the fridge?” That’s the Indiana Jones equivalent of “jumping the shark,” coined after Indy got in a lead-lined fridge to escape a nuclear blast in Indiana Jones and the Kingdom of the Crystal Skull. Believe it or not that was a lot more plausible than this scene in Ad Astra, but fans hated it. This scene makes Roy look reckless, ill-prepared, and it just isn’t satisfying to the audience. His ship really needs to be an antimatter drive to satisfy other problems anyway—just get him home that way.
Ad Astra had plenty of wonders: space towers, a pirate battle on the Moon, a base on Mars, and gorgeous shots of planets. The problem is that the thing that sets the whole plot in motion, that you need to go to Neptune to the search for extraterrestrial life, just isn’t true. There could have been solid science reasons to motivate nearly all of the film’s more far-fetched plot points. They could have had the towers be space elevators, the monkeys could have been on a transport ship moving along the same route, and a fire could have actually killed the crew. And Clifford didn’t have to be looking for extraterrestrial life at all—he could have just been exploring the solar system. What’s wrong with that?
In the end we have to settle for Ad Astra being almost amazing.
Andy Howell is an astronomer at Las Cumbres Observatory, professor of physics at the University of California, Santa Barbara, film critic at Film Threat, science advisor for movies, and host and co-creator of Science Vs. Cinema.
Correction: We’ve updated the distance between the Hubble Space Telescope and the Earth. Gizmodo regrets the error.