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In the first sequence of Total Recall (1990) we see a shot of the two Mars moons (Phobos and Deimos) in the horizon.

Is this the correct moon sizes for an observer in the surface of Mars? Shouldn't both moons be much smaller than this?

Here is a snapshot:

Phobos and Deimos in Total Recall (1990)

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  • 1
    But I thought the names of the moons were Cluros and Thuria!
    – Tango
    Nov 1, 2012 at 3:19
  • 1
    Is that seriously your main complaint about the science of Total Recall? Nothing about poor air causing triple-breastedness or psychic siamese twins, for example? Nov 1, 2012 at 9:37
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    @DanielRoseman The mutants are a result of the radiation both coming through the domes and also from this magical "Tribidium" stuff, not of the poor air quality. The psychics, that's a different matter. Actually, I just re watched this last weekend and I'm surprised how accurate they got a lot of the technology. Right down to the vertical ad panels you see in malls and the back-scatter-like X-ray machines.
    – DampeS8N
    Nov 1, 2012 at 13:19
  • Total Recall isn't the only movie that makes this error. I can't recall any movie set on mars that didn't.
    – matt_black
    Nov 2, 2012 at 0:32

4 Answers 4

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Yes, they should be much smaller. From that shot, it looks like the moons are roughly the size of our moon seen the surface of Earth. This simply isn't right. Although Phobos and Deimos both orbit Mars closer than the Moon orbits the Earth, they are much smaller and less bright:

  • Earth's Moon: 3,474 km in diameter; average distance from Earth is 384,400 km

  • Phobos: 22.2 km in diameter (156x smaller); average distance from Mars is 9,378 km (40x closer)

  • Deimos: 12.6 km in diameter (276x smaller); average distance from Mars is 23,459 km (16x closer)

The closer distance can't compensate for their tiny size. What's more, both of them reflect less light (about 5%) than the Moon, making them even less visible. Here's a time-lapsed picture from the Mars Exploration Rover Spirit (from NASA) of the moons:

enter image description here

They would be brighter than any star, but nowhere near what the moon looks like from here. So no, they wouldn't look anything like they do in the movie.

Sources:
http://earthsky.org/space/phobos-and-deimos
http://en.wikipedia.org/wiki/Moons_of_Mars

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Yes, the view is not to proper scale. This animated image from Wikipedia as recorded by the Martian rover Spirit shows Phobos and Deimos in motion against a starry background. Only Phobos would show a visible disc to the keen naked eye and both moons would appear much smaller than in the movie.

phobos and deimos against a starfield

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It's impossible to tell from the snapshot.

Certainly the moons wouldn't look like that to a human observer, but the photograph could have been taken with a long telephoto lens from some distance behind the two spacesuited figures.

(Though I admit it's more likely that the movie portrays the moons inaccurately -- or that the inaccurate size is part of the simulation.)

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  • That last sentence is like explaining away inaccuracies in the Matrix movie as glitches in the system. Very dubious. Nov 2, 2012 at 0:32
  • @RoyalFlush: The point of the simulation in Total Recall is to give the customer a good experience -- and making the moons look more dramatic could well be part of that. Still, that point was pure speculation on my part. Nov 2, 2012 at 0:35
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I'd say they should most definitely be smaller.

Take a look at this photo from Opportunity

photo

(Wiki article to context)

That smudge on the bottom left of the sun? That's Deimos.

Deimos is also the smaller and more distant of the two moons, so its size (assuming the top left moon in your screenshot is it), at least, is way off.

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