In the film Moon (2009), we see Sam Bell becoming ill towards the end. The symptoms are reminiscent of radiation sickness.

Was the source of the illness explained?

Since he was a clone, did he inherently start off with a shortened lifespan due to the cloning process?

Of course, answer would be spoilers.

  • 8
    Isn't this question a major spoiler? Feb 13, 2012 at 21:03

7 Answers 7


According to the TV Tropes page about the movie:

The DVD commentary states Lunar Industries figured three years was the longest they could expect someone to "want" to work on an isolated moon base, so they designed the clones to last just that long.

(Emphasis mine.) It's never made clear in the movie as far as I recall. This reminds me of the failsafe built into the dinosaurs in Jurassic Park (the novel, at least). They were all engineered to be lysine-deficient, so that if any escaped, they'd only live a short time in nature -- i.e. without the lysine-enriched food of the Park. Likewise, it seems that the Sams were built with some sort of slowly-accumulating illness to prevent some sort of escape at the end of their time.

  • 6
    That also could be a callback to Blade Runner which had the designed limited life-spans of Replicants as a major issue.
    – K-H-W
    Jul 25, 2012 at 15:09
  • 1
    I have to re-watch the movie but I think somewhere in there it's clear that the clones only live as long as the work was supposed to take, then they awake a new clone.
    – jsedano
    Aug 21, 2013 at 15:16
  • @KHW — Yep, the limited life span of the replicants made me think of Moon. ;-) In Blade Runner, the replicants are designed to live only 4 years because after 4 years they start feeling emotions. Feb 23, 2014 at 21:47
  • 1
    We can't exclude the "deliberately shortened lifespan" possibility, but I think radiation sickness is more plausible -- see my answer below. Jun 11, 2014 at 9:18

The source of Sam's illness is never explained in the movie, but it could be radiation sickness.

XKCD has produced a very useful infographic on radiation doses.

This source estimates the radiation dose from simply living on the Moon at about 300 mSv/year. That is well above what is normally considered a safe limit of 50mSv/year, and would elevate the risk of cancer and the like, but it would not produce the symptoms of acute radiation sickness which we see in Sam.

However, this source estimates the radiation dose from being on the lunar surface during a solar flare at up to 10 Sv. That dose would be rapidly fatal, even with the best medical treatment. The article points out that long-term residents on the moon could monitor solar activity and stay in underground shelters when there was an elevated risk of solar flares.

It appears the corporation which put Sam and hundreds of other replacement clones on the Moon considers him to be expendable. So, they might expect him to keep working even in periods of high solar activity. It is plausible that Sam was caught outside during one or more solar flares, with little or no protective shielding. This would produce the symptoms we see in the movie.

(Incidentally, it would also demonstrate Sam's "employers" were cold-hearted and evil even by the standards of science fiction corporations.)

This doesn't exclude the possibility that, as a clone, Sam would have a shortened lifespan anyway. However, the famous Dolly the sheep had about half the normal lifespan for her species. All else being equal, we could expect Sam to survive for at least 30 or 40 years. It would also be rather odd if the shortened lifespan for a clone manifested as symptoms similar to radiation sickness, rather than cancer, a heart attack or the like. So I think the filmmakers are strongly suggesting Sam's illness is caused by radiation.

  • If you're going to put something in a spoiler, don't put something else that's the same thing out of the spoiler. But really, don't bother because this page mentions the spoiler topic about a dozen times. Making it spoiler-free is hopeless. Jun 12, 2014 at 4:28
  • Fair enough, de-spoilering. My intention was to reveal "Sam is a clone" but not "there are also many other clones", but I agree it's rather pointless. Jun 12, 2014 at 8:22

I assumed that the clones had a shortened lifespan, of the roughly three years that Sam thought was his shift. We don't know how human clones would age, but Dolly the sheep, cloned by the Roslin Institute, died early. While this could have simply been misadventures (she died of a known sheep disease), on post-mortem she was found to have short telomeres - a region of the chromosome that tends to shorten at each cell division, and so becomes shorter with age. I believe there was some speculation that this was due to the age of the parent cell used in the cloning process, which obviously was older than the usual egg/sperm cells involved in reproduction.


Moon director Duncan Jones covered this in a series of interview and the director's commentary. In short, the clones are expected to start breaking down around the three year mark. What's not clear is whether this is a designed behaviour or simply a holdover of the process used to clone them but the clear implication is that it's fully deliberate on the part of EvilCorp.

Whatever's causing the breakdown, it's not down to the radiation on the moon since it would affect him on Earth too

The small canister that Sam 2 carries under his arm as he prepares for his escape is meant to contain Helium 3, the resource being mined on the moon, and valued at roughly $15 million. “The idea was that when Sam got back to Earth he may only have three years to go but he’ll be three years with a lot of cash.”

31 Things We Learned from Duncan Jones’ Moon Commentary

Sam has a three year "lifespan"

DUNCAN JONES: That was an opportunity to give Sam a physical prop to explain his degeneration as a character. The idea is that he has this three-year lifespan and he starts to break down; the molar was a way to show that. We were talking about wanting to avoid exposition. There was a case of I could have either done that with a dialogue scene between the Sams, or I could just show him losing a tooth. That was the way we tried to get around those exposition moments.

Director Duncan Jones takes viewers to the far side of the “Moon” – Interview, Part 2

Evidently the key was that Sam's motivation (his wife and family) would start to wane dramatically if his stint went on longer than three years.

In my mind, he was a test pilot who became an astronaut but gradually he became a kind of miner; a working class guy. It wasn’t as specific as you’d think but it left room for your imagination. We did talk about how long he hadn’t seen his wife… I thought it was that he thought he was going to [the moon] for only two months or six months and it became three years. I thought, `Why would anybody go up there for three years? That’s crazy,’ but Duncan said he knew it was three years and that’s when it became about the money..”

Jones also talked about Bell’s back story, saying, “His relationship with his wife was a driving factor to why he took this job at the beginning… Yes, he was going to go up there to get the money to buy a house.”

Moon Interview: Director Duncan Jones and Star Sam Rockwell!

Out of universe, Sam's lifespan (and contract length) both reflect the director's own life experiences.

Duncan Jones: Absolutely. Yeah, I’m gonna start off with a fairly pat joke, you’ll have to forgive me. It’s no coincidence that Sam’s contract is three years cause that’s how long I spent in Vanderbilt at graduate school. That is seriously where I got the idea. 'Cause I was very isolated there. I was working in graduate school, I was staying in a flat on my own, I had broken up with my girlfriend, and then I felt incredibly alienated. So that was a good inspiration to how Sam was feeling.

Duncan Jones - Moon Interview


Cellular degradation or a compromised immune system is a suspected side effect of cloning. A cloned genome would rapidly divide to the state the original individual was duplicated from, but wouldn't necessarily have the innate ability to age as a proper organism would from birth. Just speculation, but the multi-celled organisms that have been cloned thus far have all had significantly decreased life spans compared to their originals.


Gerty did say, "Genetic abnormalities and minor duplication errors in the DNA can have considerable impact." Alluding to the impacts of cloning rather than radiation.

  • And that would give symptoms similar to radiation sickness? And limit lifespan to 3 years?
    – DavidW
    May 11, 2022 at 22:29
  • Who really knows... Both are definitely plausible. Probably a combination of both. I think we might be digging too deep, haha. May 11, 2022 at 22:34
  • The radioactive tampon bit, is another clue pointing to radiation poisoning. May 11, 2022 at 22:49
  • It has to be a combination of both. Final answer. May 11, 2022 at 22:51
  • This seems to be a comment on another post rather than a complete answer in itself. You'll be able to leave those on other's posts when you've sufficient reputation. 'Till then please just ask and answer as appropriate. May 11, 2022 at 23:22

I think is more radiation poisoning than anything there would be no desire for the other clone to leave if they figured out they only had 3 years to live he would just stay or let the "rescue" team do what ever they was gonna do to him

  • 1) It would be best to explain why you think it's radiation poisoning specifically. 2) The whole point was that the clones were never supposed to figure out that they only had three years. It was only because of a malfunction that anyone ever noticed anything amiss.
    – phantom42
    Jan 23, 2018 at 23:56

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