Goofs

When the spaceship first lands, the interior set is cocked at a 20° angle. But each time the astronauts exit into the snow landscape the ship is sitting straight up.

The camera shot of the clearing seen through the binoculars at the films beginning is the same one used to watch Mories run away from the underground entrance.

From inside the spacecraft the windows are clear, but seen from the outside they are opaque.

During the ambush of Borden, two mutants fall off the rocks after being shot, but there is no sound of gunfire.

When the astronauts first descend the mountain below the snowline they spot a clearing in front of them through their binoculars, and claim that it is several miles away. There are no binoculars in the world that can produce the view shown, which is no more than 100 to 200 yards away.

When the astronauts walk through the cemetery the headstones are clean and unblemished, and the engravings on them are perfect and unworn after 500 years have past. There are also spotless wooden crosses which would have long since decayed or been eaten away by insects.

When the men encounter the giant spider, it lands on Herb Ellis, and John Borden fires three rounds at it. Herb kicks it off and Borden then assists Dr. Galbraithe in cutting Henry Jaffe out of the web. Another spider appears and Borden fires five more shots at it, for a total of eight shots in all. Yet the revolver he used, a Smith & Wesson Military & Police, only held six rounds and there was not enough time to reload.

A crew member of the spacecraft says if they had landed on Mars, the atmospheric pressure would be only 10% that of Earth's. In fact, it is less than 1%.

The spacecraft crew are seen reclining to compensate for the high acceleration when they leave Mars orbit. This is scientifically valid and widely implemented in real-world spacecraft, but the crew would need to lie perpendicular to the acceleration forces, i.e. the cabin would have to be accelerating upwards relative to the camera position. Shots of the men leaving the crashed spacecraft reveal that the cabin was oriented upright and must have been accelerating forwards, so the acceleration should have slid the men out of their seats backwards towards the camera.

A revolver is shown that has a blown barrel due to what was said to be lack of strength in the metal as well as too strong a propellant powder. If the metal in the gun was weak, the part to fail would have been in the cylinder and frame area, not the barrel. The most likely cause of the damage that was shown would have been an obstruction in the barrel.

In the early scenes of the spaceship in orbit around Mars, and then blasting away from the planet, there is a bright blue sky visible through the portholes at all times, instead of the blackness of outer space.

Leather "bomber" jackets with fur collars and camping gear would not have been standard issue for a reconnaissance mission to Mars in a ship that was not expected to land.

Although the underground civilization is 500 years in the future they still use conventional glass lab equipment.

When John Borden (Hugh Marlowe) challenges the mutate leader, Naga, to hand to hand combat, he mistakenly calls his partner Herbert Ellis (Rod Taylor) Hank.