Before I go any further I should say I enjoyed the film – it was hokum but entertaining hokum. Howewver, the pedant in me can’t let the bad science in it go.
First off there is the fact that Mars is inhabitable at all – we now know that has a thin wisp of an atmosphere containing carbon dioxide and not much else. Not to mention the average surface temperature makes Antarctica seem tropical. But that is what we know now. The novel on which it was based, Edgar Rice Burroughs’ “A Princess of Mars” was first published as a magazine serial one hundred years ago. At that time Percival Lowell was producing maps of Mars showing an extensive canal network and advancing as a serious hypothesis the notion that they were carrying water from the ice-caps to the cities and farms of a dying civilisation. Let’s give the film a pass on that – call it an alternative reality, and move on.
Next was how John Carter got to Mars, or Barsoom as the natives call it. In the novels he was able to teleport backwards and forwards. No explanation as to how Carter got this ability was advanced. It was just a means for Burroughs to get his hero to Mars and into the adventure. In the film the teleportation was achieved by means of an artifact belonging to the “therns”. These beings appeared as human but could change their appearance and would appear to be some alien species parasitising on the Martians. One of them hinted quite strongly to Carter that they intended to move on to Earth when Mars was used up. These beings could travel quite freely between worlds using these artifacts which worked by means of a “Ninth Ray”. This is just pseudoscientific arm waving. (Yes I know the ninth ray was in the books.) One final problem with teleportation – the velocity difference between Earth and Mars would result in Carter being splatted on impact.
Carter has problems with the lower Martian gravity initially but then makes use of his greater strength by leaping and bounding all over the place. Plausible – to an extent. However, Olympic high jumpers jump about 2 metres – which raises their centre of gravity a little over one metre. In the lower Martian gravity they would manage to elevate it 2.5 to 3 metres – giving a maximum jump of 4 metres. Carter, however manages to jump twenty or thirty metres, sometimes from a standing start. The long jumping is even sillier – the world record is under 9 metres so on Mars one might plausibly say that such an athlete could leap tweny five metres or so. An encumbererd Carter manages to leap about half a mile across a city.
Carter also manages to break chains and pull boulders apart even though gravity has no effect on intermolecular bonds and such feats would be just as difficult on Mars as they are on Earth. He al;so whirls a boulder and chain around his head in an arena fight. Judging by its size, it would mass something like three tons and would have the same inertia on Mars as on Earth and thus would be just as difficult to accelerate. Even in the Martian gravity it would weigh over a ton and thus be impossible to lift.
The Martian moons appear as large objects in the sky. In reality they are so small that Phobos would appear about a third of the size as the Moon appears on Earth and Deimos would be little more than a bright star. In the film they always appear as a close pair whereas in reality they have independant orbits.
Finally, Barsoomian vertebrates – including the Green Men – are six limbed. One exception is the Red Men who are caucasian Homo Sapiens in appearence. It is not revealed whether or not they are oviporous like the Green Men (in the novels they are – which means that their internal biology is so alien that it would be impossible for an Earth human to have a child with a Barsoomian.) I do wonder whether future films will suggest that the Red Men are descended from Earth humans brought to Mars by the therns.