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Review: Red Planet

Red Planet logo As I said in the intro, I was expecting a really bad movie, both plot-wise and astronomy-wise. What I got was an enjoyable movie. It is not very fast paced, which may be why the critics didn't like it. The plot was not great, but good, and I thought the pacing was just fine. I expected Val Kilmer to chew up the scenery, but his character was actually a rather modest, likable fellow, and Kilmer played him very well. The special effects were also really good.

The basic plotline is that Earth is dying. Mars is humanity's last hope, so a terraforming project is initiated to make Mars habitable. Low grade nuclear weapons are detonated a the north pole of Mars to release the frozen carbon dioxide there into the air (which is actually plausible), which in turn will warm the planet through the greenhouse effect. Then, years later, probes loaded with algae are dropped on the planet, which will hopefully turn the CO2 into breathable oxygen.

For reasons unknown, the oxygen levels drop, so a team is sent to Mars to investigate. Then things start falling apart.

First: a brief look at the premise. The idea is that we need to make Mars more Earthlike. It is true that there is quite a bit of carbon dioxide locked up in the martian south polar cap (note that in the movie, they melted the north cap, which has less CO2). One study, done by Mars Society founder Robert Zubrin, estimates that by heating the south polar cap (using mirrors, not nukes!), it is possible to release enough CO2 to generate an atmospheric pressure of about 1/3 to 1/2 that of sea level here on Earth, and it may only take a few decades to do it ( the study is available online, but is a bit technical). There would also be a temperature increase as well, and it may be enough to exceed the freezing point of water. If this were done, it would warm enough and the air pressure high enough that a person on the surface would only need an oxygen mask, and not a full body pressure suit.

So, assuming dropping nukes on the martian pole accomplishes this, the basic premise of the movie is indeed realistic, assuming that oxygen were substituted for CO2 (and that is explained in the movie). It would be colder than depicted in the movie, however, and exercise (like walking 100 kilometers, say) would be very difficult, since the air pressure would be low. Given these caveats, let's continue.

As the spaceship is inserting itself into Mars orbit, a ``gamma burst'' from the Sun fries almost all the main electronic equipment. Sparks and shorts erupt as Commander Bowman tries to correct the problem.

Gamma rays are high energy photons emitted by the Sun. Sometimes, during in an intense flare, there can be a large amount of gamma rays produced. These photons can indeed damage equipment, but the size of the burst would have to be unprecedented to do as much damage as shown in the movie. Remember too, the ship was designed to go to Mars, and the design engineers would know that the Sun can be unpredictable. They would use radiation resistant equipment.

The situation in real life is complicated. Usually, a large flare from the Sun is accompanied by a burst of high energy particles like protons. These impact spacecraft, building up a static charge, like when you shuffle your feet along a carpet on a dry day. Enough charge builds up, and zap! It discharges, shocking you. That discharge on a spacecraft can damage its computers. The particles from the Sun can travel as fast as 1/3 the speed of light, so you might have a few minutes warning after seeing the flash of light from the flare before the particles hit. This doesn't matter, really, since in the movie they said it was the gamma rays that did the damage. Anyway, the usual amount of damage from such flares is minor, amounting to local, not global, damage on a spacecraft.

Also, for a burst to do that much damage to the ship means it would have more than enough energy to provide a lethal dose of radiation to the astronauts. Crashing on the planet would be the least of their worries!

Incidentally, the commander's name, Bowman, is a clear tip of the hat to the movie ``2001: A Space Odyssey'', which also had a commander named Bowman.

When Bowman sees a fire, she uses a fire extinguisher to put it out. The force of the spray sends her flying backwards.

Actually, I like this. It's accurate, since the force of the spray would send her flying in weightlessness. Moreover, they flew the whole way to Mars under artificial gravity, so she wasn't accustomed to being weightless. I think that was an honest mistake on the character's part during a moment of stress, and very believable.

image of spaceship with wheel Incidentally, they used spinning wheels on the ship to simulate gravity, which would work. I was amazed to see two wheels, spinning in opposite directions. This is exactly what you want to do! If you have only one wheel spinning, the ship itself will try to spin in the other direction (this is called ``conservation of angular momentum'', for those of you that love jargon). Having a second wheel spinning in the opposite sense counteracts that. Also, a single spinning wheel makes it very difficult to steer the ship, so having a second one again counteracts that. Very well done, and fine attention to detail on the part of the crew of the movie.

When the escape pod hits the ground, it bounces around, and eventually rolls off a cliff.

The airbags deployed by the escape pod were of course patterned after the same ones used by the Mars Pathfinder mission which touched down in July 1997, and which worked perfectly.

The effects here were great, but I question the speed. Mars has a surface gravity of about 0.38 times Earth's, so the pod would bounce higher and fall slower (a reference to this is made later in the movie when the astronauts, um, vent some human liquid waste). Knowing the pod is about 4 or so meters across and using that to judge their speed on the movie screen, it looked like the pod fell too quickly.

Also, the lower gravity may not have helped them much when the pod rolled off the cliff. Let's say the cliff was 100 meters high (and it looked higher than that to me). By the time they hit the bottom, they would be falling at a speed of about 30 meters per second, or as fast as a car drives on a highway. Even with the airbags, it's hard to believe they could survive that sort of beating. People do survive car crashes at that speed, of course, but they usually don't walk away from them!

Our Hero and the red sky of
Mars Bad:
As they leave the pod, we see the astronauts silhouetted against Mars' pinkish-orange sky.

Well, this is close. There has been much argument over the color of the martian sky, and I have seen different people claim it to blue, pink, red, orange, brown and even purple.

According to the ``official'' NASA Mars website, the sky of Mars is butterscotch. On Earth, our sky is blue due to the scattering of sunlight by nitrogen molecules in the air. On Mars, there is fine dust suspended in the air, which both scatters and absorbs sunlight. This is more complicated than what happens here on Earth, and the result is the creamy yellowish color. This was the color seen by both the older Viking probes and the more recent Pathfinder lander, as you can see from the picture of the martian landscape from Pathfinder below. true color image from Mars Pathfinder

This is just good: Commander Bowman sends a message off to Earth, and says, ``Too bad I have to wait 40 minutes for an answer''. Earlier in the movie they say they have traveled 309 million kilometers. Assuming that's the distance from Earth to Mars (since they traveled on a curved path, the actual travel distance is greater than that) then it will take light about 17 minutes at 300,000 kilometers per second to get to Earth. Then the folks at NASA answer, and it takes another 17 minutes to get back to her. So 40 minutes is a pretty good estimate of the round trip time!

When Commander Bowman gets the main power back online, the wheels start spinning up again. Everything immediately falls to the floor, including her.

In a spinning wheel, the gravity wouldn't just turn back on like a switch. The wheels would start spinning up gradually, reaching full speed after some time. Even if they could start spinning at full speed instantly, the simulated gravity wouldn't just turn on like it did in the movie. The gravity is being simulated by centripetal force, which is the same force a car applies to you pushing you to the left when you make a left hand turn. [Note added January 13, 2001: I initially had an incorrect explanation of centripetal force here, but a reader corrected me. I decided to overwrite the old explanation to lessen the confusion!]

Imagine you are inside a giant wheel floating in space. If there is no air inside the wheel, it can spin as fast as it wants and you will feel no force! As long as you don't touch the walls, the wheel cannot accelerate you. Now if you add air, the friction of the air against the walls will push on the air, spinning it along with the wheel. That air will push against the air just ``above'' it, and so on. If you are floating in the wheel, you will feel a breeze which will blow you toward the wall. Eventually, you'll hit the wall and roll along it until it spins you up to the same speed. Then you will feel something like normal gravity.

I know, I know, this is weird and hard to picture. I had to sit and think about this for a while too, and the above explanation is what I came up with. I'm pretty sure it's correct, but I might be wrong. I've never been in an accelerating wheel in space before!

[Note added December 13, 2000: a reader pointed out to me that the wheels were not just big cans, but divided into compartments. In the infamous shower scene early in the movie, Bowman and Gallagher are standing, so there was gravity: they must have been in the wheel. Yet he goes through a hatchway to get into and out of the room. This changes my imaginary experiment above. The wheel is divided into wedges like a pie, where the edges of the wedges are the walls of the rooms ( and the chalice from the palace has the brew that is true ;-). When the wheel starts spinning up after being stopped, you would see a wall coming at you, and then you would roll ``down'' it until you hit the floor. Nevertheless, in the movie when the wheel was started up everything fell instantly, which is still incorrect.]

This is just good again: when they crash on the planet, one of the astronauts talks about the ``landing ellipse''. That was a nice detail. When you are crashing on a planet, there is more uncertainty in your position along the direction of travel then perpendicular to it. That stretches out the probable footprint of your descent, making it into an ellipse. That was a very nice touch.

After crashing, they have to walk a ways to get to the habitation module. Chantilas is dying, so they leave him behind.

Well, this would be crass, but Chantilas has a suit full of oxygen that they left behind. They weren't sure they'd get to the hab with the oxygen on hand. I'm not necessarily saying they should have shot Chantilas and taken his air! But later in the movie, another astronaut gives Gallagher his air supply and kills himself. I would think that Chantilas, a realist (he knew he was dying and told them to leave him), would also do as much. This doesn't really affect anything, and you can mark this as a plot quibble.

When they get to the hab, they are shocked to see it has been destroyed.

The hab module is the single most critical piece of equipment to future colonist of Mars. It will make air and have food in it waiting for them when they arrive. I would think that NASA or whoever built it would have constant telemetry links to it. If it were destroyed, they would know pretty fast, long before the astronauts actually got there.

As Gallagher is dying of hypoxia, he decides to quicken things up and opens his helmet. To his shock, he can breathe.

The main plot of the movie was that the pressure should be low, but the oxygen had mysteriously disappeared from the atmosphere. However, the bugs that ate the algae produced prodigious amounts of oxygen, so there was O2 to spare. However, we would have known that! Even from Earth, telescopes on the ground and in orbit would be able to detect the signature of oxygen in the air. After all, they somehow knew the oxygen had disappeared; why didn't they know it was back? My thanks to Bad Reader Sean Hill who pointed out to me that the correct medical term for reduced oxygen to tissues is hypoxia; I had it written originally as anoxia, which is actually a complete lack of oxygen.

In an attempt to communicate with the orbiting mothership, they pull the modem from the Sojourner rover from Pathfinder and use it to radio for help.

Well, I liked the part where they walk up to the rover, which made such huge news in July 1997. I also thought it was funny that they didn't know its name (at one point Gallagher refers to it as ``what's-its-name''). But I don't think you can just pull the modem off the rover, point it up and hope to get a good signal. After all, the rover's batteries were dead! Also, they disconnected it from the antenna. It looked like there were solar cells and an antenna on the radio, but later he tries to use it at night, so if those really were solar cells, they wouldn't have worked anyway.

And it's actually worse than that. The rover radio had a very limited range, about 10-20 meters. It was only designed to communicate with the lander, which was why the rover never strayed far from the landing site. The original Pathfinder mission ended because the lander's battery finally failed; so even if the rover's radio worked, the lander wouldn't be able to relay the signal to Bowman in the orbiting Mars ship. Also, the rover radio wasn't designed to transmit voice; it had a limited capacity to send information. So even if Gallagher got the thing rigged up to use a microphone and found power for it, it would have stopped working when he walked more than a few meters away.

I found this technical info about Mars Pathfinder at the Microrover Radio and Antennas website, part of the larger Mars Pathfinder website, which in turn is part of the much larger NASA Mars Exploration website. My thanks to Bad Reader Jason Slovacek for pointing this out to me.

Later, at night, Gallagher tries to get ahold of Bowman in the orbiting ship, but cannot reach her. He says ``She must still be on the dark side.''

I laughed when I heard this. It's nighttime where Gallagher is, so he's on the dark side of Mars too! It's possible for the ship to be out of range, or over the horizon, but his saying that was a bit silly. I think he meant to say she was on the far side of Mars, out of range. This is a common misconception with the Earth's Moon as well.

The second-to-last survivor is attacked by the bugs. He lights a flare and sets off a huge blast of combustion, which can be seen from orbit by Bowman.

An impressive scene, with cool effects, but if Bowman can see it from orbit, I would think Gallagher would literally be toast. He was at ground zero!

But there's perhaps worse science here. It is a very common misconception that pure oxygen will burn very fast. That is not true. Something that normally burns will burn much better in the presence of a lot of O2. Pure O2 won't burn at all. So if the bugs themselves were flammable, then they would certainly burn a lot better as they release the oxygen inside them. However, I don't know how well a bug would really burn. I doubt they would burn well enough to cause such a huge conflagration. However, they are science fiction bugs, so maybe they make methane too. Still, that scene is pretty unlikely.

Bad: Our Hero in front of the Russian Kosmos probe After Gallagher treks 100 kilometers to the Kosmos craft, Bowman tells him to connect the Sojourner modem to the Kosmos.

This isn't astronomy, but have you ever installed a modem? Even when they are designed to be used for a certain type of computer they're impossible to get working. Yet he gets it hooked up to a decades old Russian probe in seconds. I know he's a good engineer, but modems are really just evil that way.

Gallagher is able to reprogram the Kosmos probe using its display console.

Why would an unmanned probe have a display console? Who's going to use it? Probes are programmed via radio, and no human contact is needed. Note that the display has an audio speaker too.

After Gallagher blasts off the planet in Kosmos, Bowman grapples him. She orders the computer to reel her back in, and instantly they start back.

Bowman is holding onto the Kosmos structure with her hands. That structure along with Gallagher must have massed about a ton. Although it's weightless, it still has mass, which means that she never would have been able to hold on when the reel snapped her back. It would be just the same as if she were on Earth trying to perform the same task. The structure still has a huge amount of inertia, and would have to be moved slowly back to the ship, or else she wouldn't be able to retain her grip.

Last but not least: after performing CPR on Gallagher, the computer tells Bowman to "stand him up."

This scene was in microgravity. Standing him up would make no difference, because there is no "up" in that environment! Actually, it might be easier to resuscitate someone in microgravity, since their heart doesn't have to work against gravity to pump blood. Incidentally, she didn't do the CPR correctly either. You start by giving a few puffs of mouth to mouth, then pump 15 times, then give two breaths again. After that you repeat the pumps and breaths. She pumped too slowly too.

Incidentally, it would have been hard for her to compress his chest in microgravity, of course. I made a note of this when I first saw the scene, then decided she must have braced herself with her feet and the director simply didn't show it. After all, they made a big point of this in the fire extinguisher scene... but the fact is, they didn't show it, so technically (and tentatively) I'll label it Bad Astronomy here too.


As I said before, all these problems notwithstanding, I did like this movie. While not action packed, I liked the pacing and the thoughtfulness of it. There were a few plot devices: (1) the gamma flare (2) why didn't the military disable AMEE's military mode before giving it to civilians? and (3) the bugs making oxygen. However, this is a factor of ten fewer plot devices than in most movies.


There are a few other websites about the movie.
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