PostHeaderIcon What If We Had No Moon? (Oblivion Spoilers)

I was alerted last week to the possibility that people might be asking questions about the scientific possibilities suggested in the movie Oblivion, released today. May I point out that ripping apart the science in movies like this is a form of entertainment for me? If you aren’t interested, go read someone else’s blog.

Shameless plug: You should go see Oblivion at Pacific Science Center in IMAX.

In order to address these issues, I have to talk about the movie, but I’m going to do my best not to spoil the whole thing since you might want to see it.













In Oblivion the year is 2077, and the Moon has been destroyed by robot aliens. This caused widespread destruction due to earthquakes and tsunamis. The tectonic activity has stabilized, but humanity has migrated to Titan. A few people are still on earth guarding the Hydro Rigs that convert seawater into energy for the Titan colony. The Moon is depicted as being half there, half a debris ring around the Earth.



Yes, and the movies doesn’t have any.

The method of the Moon’s destruction isn’t dwelled upon in the movie, but I get the impression it was a nuclear war. Let’s just assume the alien race has enough power to blow up the Moon, and they do so.

The first effect is going to be a huge number of meteorites slamming into the Earth. These aren’t going to be just a few that make some pretty craters, that’s a lot of mass up there in the Moon and a lot of it is going to come raining down on the Earth. I think this is going to be the most devastating effect. I’ll have to run some hypothetical math (or maybe Phil Plait or XKCD What-If will do it before me), but it seems like this rain of debris would be significantly more destructive than the meteor that probably killed off the dinosaurs. There will be more mass than that single meteor (a LOT more mass), and it will rain down over more of the planet. I suspect it will be moving more slowly though, so that may mitigate the effect a bit.

Last I heard the dinos died out either because of the ensuing nuclear winter (too much ash and dust in the atmosphere, cooling the climate) or a nearly instantaneous ignition/superheating of most of our atmosphere, which would have broiled everything aboveground leaving burrowing animals and sea-life alone. Whoo-ee. Someone check my references on that. (Jonas? Jonas? Why are you in New Zealand when I need you?). So, the Moon debris falling down would be very bad.

But somehow no meteorites from the lunar explosion.


Sure. There could be earthquakes if the Moon blew up. Mostly due to IMPACTS FROM METEORITES. Barring those I’m having trouble envisioning why we would get earthquakes from the Moon breaking up in orbit. So my answer is:

Not the way they are in the movie.

The Moon does pull tidally on the Earth’s crust a little bit, but the effects are not the kind that we generally notice over the span of human lifetimes. Even by spreading out the mass of the Moon into more of a ring, you’ll also lose that tidal flex. I would expect that to make fewer earthquakes, not more. In the process of the Earth settling from a shape influenced by the Moon into a shape influenced by the debris ring we will have some earthquakes, but not ones that destroy cities.

If we were Jupiter’s moon Io, and it was Jupiter that was destroyed then yes, we would feel significant tectonic stress. But we’re not.

The Moon’s tidal forces do assist in keeping the Earth’s crust heated, and possibly impact the fact that we have moving tectonic plates in the first place. Now that tectonic plates have formed though, it will take a bajillion years to slow them down and stop them.


Let’s say yes.

We all know the Moon is the major influencer on our tides here on Earth. The Moon and the Sun share the duties of causing the Earth’s tides, but the Moon does 2/3 of the work, and the Sun only does the leftover 1/3. So there’s a lot of water caught up in the tidal oval at any given time. The Earth rotates through that oval of influence, giving us two high tides per day.

Here’s a diagram of the tidal oval. It’s exaggerated a lot:



That’s a LOT of water to displace, and most of it is at the equator. So if the Moon suddenly disappears, that peak will slosh back down and (after sloshing back and forth a lot) will settle into a more even distribution. With half the Moon still in place, we’ll only be redistributing about 1/3 of that water. Also, since the Moon’s debris is staying in orbit (forming a ring), we won’t need to displace the water towards the poles, it can stay concentrated near the equator. Even though that is a significant reduction, it’s still a lot of moving water, suddenly. That’s a tsunami: a LOT of ocean water being displaced suddenly.

A caveat: it looks in the movie as if those tsunamis carried a lot of sediment with them, enough to cover all but the very top of the Empire State Building. Tsunamis from the destruction of the Moon would have no reason to dredge up sediment from the bottom of the ocean, so I don’t know where it is implied that material came from. I have no problem with the water washing that high in a significant Moon event, but not mud or sand.

A Ring around the Earth

When you first see the movie you’ll say “Alice! That ring is around the Moon, not the Earth.” Just wait, later on it becomes visible as a ring around the Earth.

Yes and no.

I guess that’s my answer for all of these. This is the case where I need to pull out my solar system dynamics textbooks and run through some equations first though.

Yes: soon after the destruction of the Moon, any debris will end up in orbit, and a lot of that will be leading or following the Moon’s own orbit, since that’s where it originated. This will give us a lumpy ring. It won’t be as bright as in the movie, because it will be mostly dust and boulders. Saturn’s ring is very visible because it is mostly very reflective ice. Dust is darker.

Over 60 years (from the Moon’s destruction around 2017 or later until the time of the movie in 2077), some of that debris will have reentered the Earth’s atmosphere, and the rest will also still be orbiting in that ring.

Over a more extended period of time I don’t think the distance of the Moon’s orbit is a stable place for a ring system. The dust will either recoalesce into one or a few Moons, drift to a different orbit, or fall down to the Earth.

I haven’t had time to sit down and calculate any of this out, but these are my reasonably-well-educated guesses.


If We Had No Moon, Bernard Foing

Sun’s Tidal Effect

365 Days of Astronomy














~ A l i c e !

17 Responses to “What If We Had No Moon? (Oblivion Spoilers)”

  • Lionel L. says:

    If most of the mass of the moon is still up there, and a large part of it is clumped around where the whole moon used to be… Wouldn’t the what was left of the moon re-coalesce into a single large body?

  • krysteen says:

    The moon thing was wrong but biggest issue I had was just like Battle Los Angeles, the aliens(robot) comes all this way to fight over and steal some of the most common elements in the universe (h2 and O)…. But I did like the movie.

    • Alice says:

      Yeah, I enjoyed it too, even though the whole way through I was naming sci fi movies to which it was paying tribute.

  • krysteen says:

    HAHA. I half expected Morgan Freeman if Tom Cruise wanted the red or blue pill. Totally did the same thing.

  • gEOFF says:


    Thanks for posting this! I saw Oblivion this weekend, and had many scientific grumblies, which you helped confirm. I will also add a couple others that bugged me.

    The alien spacecraft appears to orbit just once per day, despite appearing to be somewhere in low Earth orbit, where it should have gone around once every 90 minutes or so. Also, with space navigable drones, a smart alien race would have set up a TDRS-style satellite system to avoid comm blackouts.

    The NASA hardware uses a mix of the worm logo that they did away with in 1992 and the current blue meatball logo. While it is possible that the agency would return to a mix of the two in the future, it left me with the impression that they got all their technology from the JSC gift shop.

    The dashboard on the Odyssey spacecraft displays STS-152. This stands for Space Transportation System-152. It is a mission designator specifically used during the Shuttle program. Again, this made me snort a little derisively when I saw it permanently tattooed on a future spacecraft.

    When Tom Cruise had to explain that Titan was a moon of Saturn to his wife, THE NASA ASTRONAUT AND RESEARCHER! Apparently, NASA got into the habit of hiring folks who know nothing about space or the destination they were headed to on their final mission.

    There seemed to be an awful lot of rainy weather happening on a planet that was just two weeks away from being sucked dry. While the removal of the oceans certainly would have disrupted weather patterns, I would expect more along the lines of Martian dust storms than regular rain squalls. It also seems odd that the water suckers are positioned on the coast, next to New York City. It would seem they should be at the deepest points in the ocean, like a drinking straw at the bottom of a glass to get everything.

    Ultimately, I enjoyed watching it once, found many unintentionally funny moments, and summarize it as Tom Cruise in Sand People vs. the Matrix.

    • Geoff says:

      also, stupid caps lock.

    • Alice says:

      I’m laughing so hard! Thanks for the technical details on the spacecraft and logos! I could just see the props people for this film hitting up several gift shops as they were preparing it.

      The one thing I’m still confused by is the record that Tom Cruise chooses to play. I swear the cover of the album looks just like my Mom’s Vangelis Albedo 0.39 cover (Google search). I thought that would be a hilarious tie-in… but then the song was something else. ::sad face::

      Since we only see the cover for a second, I’m betting that I’m wrong, and the cover was correct for the song, and I was just primed to see tie-ins.

      I wasn’t under the impression that it’d be dried up in 2 weeks… I thought they were just going to “Titan” in two weeks, and that they’d be replaced by another crew. I thought the period of time to suck the planet dry was indefinite. But, I only saw it the once.

      My summary is definitely “Moon meets Top Gun, with a good-sized pinch of the Matrix, Portal II, 2001, and Star Wars.” (How could you NOT think of jawas?)


  • Jenai says:


    Is it established that they did indeed blow up the moon? That was what Jack *thought* certainly, but I thought, later on, it was implied that the moon was harvested to death for energy. [They ‘ate’ the moon]. (I would assume bits and pieces cracked off over time, even a short period of time, during this process, and were eventually pulled into earth orbit or lunar orbit – The Tev may have even pulled some larger chunks into Earth orbit itself to maintain stability or for future mining). The same process was currently underway on the earth, albeit in a much longer process.

    It is a bit hard to figure out, since all the backstory in the beginning of the movie is an outright lie. It’s not supposed to be ‘feasible’, per se, hence why Harper’s curiosity was a good thing. Things didn’t quite ‘add up’.

    Whether or not nuclear devices were really used isn’t even clear. Jack thought they were; it was part of the story to explain the ‘radiation zones’ he wasn’t to go into, and the devestation of the planet. (Which was supposed to be the changing of the climate/weather/geography due to the planet being affected by the Tev’s geothermal energy harvesting, or somesuch).

    And yes, the planet was not goign to be sucked dry in two weeks. They were likely going to be terminated and replaced; it’s unlikely the effectiveness of any team lasted more than five years due to aging.

    • Alice says:

      *More spoilers*


      I completely agree. Things don’t quite add up. The funny part is, I got the heads up about writing this because the Moon would be destroyed and the person wanted to know what to say when asked about that. I think that pretty much everything set out in the premise of the movie is possibly false. How do we know the year is still 2077? It could easily be 2562. If each set of clones only lasts 5 years, they could just tell them all a false year. A different timescale would change the effect of the Moon’s changes as well. Isn’t it possible that those cities that were destroyed by earthquakes caused by the Moon’s semi-destruction were actually killed off by the Tet? (I think it’s “Tet” short for “Tetrahedron” but I could be wrong).

      So I wrote the above “science review” based on the story presented at the beginning of the movie, partly because that’s fewer spoilers, and partly because that’s the more interesting science to debunk. :)

      And those radiation zones? Couldn’t those just be faked? Or was it obvious that they were faked? I just don’t remember.


      • krysteen says:

        Nothing that comes from tom cruises character can be trusted since his memory was “wiped for security” in case of capture. It probably isn’t super far into the future if there is a separate band of humans surviving in hiding.

        The radiation zones were fake, at least one for certain to keep each of the drone techs from interacting, for obvious reasons.

  • Lauren says:


    It had to take place in 2077. While Tom Cruise could easily have his time scale wrong, and his wife could have just been frozen for longer, Morgan Freeman’s character remembered back to the time before this was going on. And if you can’t trust Morgan Freeman on something, I don’t know what you can trust.

  • saysay says:

    i knew it i told all my teachers and they didnt beileve me so hahahah lol

  • Hugh says:

    You cannot trust anything tom cruise says because he is programmed by the tet, but the year is correct for several reasons but the exact one is they say she spent XX years in stasis in earth orbit it took them decades to crack the gps encoding signal to bring down the escape pod. I am going from memory so excuse the dates not being exact but you get the jist. It appears most of the moon is still there. Morgan Freeman def says that earthquakes and tsunamis ruined earth and that Chicago was spared cuz of bedrock. This was a tactical military decision. IMO There is no way that would have caused the type of tsunami’s Toms suggest or earthquakes absolutely ridiculous. IMO The tides would get screwed a little but a tsunami and major earthquakes very unlikely because the gravitational force is evenly distributed over the ocean the tide would just change as moons pull become different. The sun is dominating factor here not the moon. And the equation for gravitational force between two bodies is based on mass which it seems a large part still remains. Tom himself being an experienced astronaut and scientist would know this too so it is implied they wiped his science education also. There is no radiation which is obvious from what Morgan Freeman says I have been to your radiation zones and he is obvi unharmed. The only true thing we know about the war is the tet came down and out came lots of Tom Cruises and he implies a ground war that was lost and also implies no nukes. They say the teams that tom works on now came later after the war was lost phase 2 to just protect the energy the tet is harvesting. It does not say it is harvesting water as you mentioned earlier. The other thing you mention is that the Building is buried under 100 feet of sand, what if it was cut on half or just the top floors cut off by some flying aircraft and it landed like that. Do not make assumptions the Tet has mastered cloning and has obviously mapped the human brain, which is something we are at least 10-20 plus years away from. To do this you would probably need quantum computing which suggests their intelligence dwarfs ours and would detroy us in a military battle. Food for thought a quantum computer could break any password in the world in fraction of a second. Any password including nukes, powerplanst, water, gas, telecomm satt, software etc… We would not know this and not be changing passwords frequently enough to combat this and they could shut down all our nukes and entire comm, energy,etc grids after the quakes and tsunamis in minutes effectively stopping us from ruining our planet with nukes and probably crushing our ground force. Also it is definite that they were either going to kill Tom and his partner or reprogram them not that the planet was out of water. The reason the tet is near land is it would be a strategic placement. the techs can fix the drones they are using to exterminate the remaining population and threat. But if you are questioning location one of the most obvious spoilers is where they live? Above the clouds lets assume these are the lowest clouds around NYC lets say the minimum is 6000 ft but from the pic I believe the clouds looked like very high ones. It would be freezing and not pool weather! Not to mention everything else that comes with the altitude

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