Maybe it’s an alien-planted monolith!

A survey of the gravitational field on the surface of the moon to determine its makeup underneath has discovered the existence of a mass underneath one of the craters.

Publishing in Geophysical Research Letters, the Baylor scientists have two theories for the origin of the huge subterranean blob. It could be the leftovers of dense oxides created in the last years when the moon’s surface was an ocean of magma — a theory that relies on the giant-impact hypothesis, when an impactor the size of Mars may have collided into a magma-covered Earth, ejecting magma into orbit that became the surface of the moon. But speaking with National Geographic, the Baylor team appears to prefer the idea that the mass is the remainder of the iron-nickel core of an ancient impactor that created the South Pole-Aitken basin.

This discovery has generated quite a bit of interest.

But as a fan of the film 2001: A Space Odyssey, my thoughts immediately went to the possibility that the mass was deliberately planted there by an extra-terrestrial intelligent life form as a signal. In the film, the discovery of anomalous electromagnetic fields on the surface of the Moon suggests an unusual object underneath and leads to the discovery of a large buried black monolith. When the covering soil is removed, the first exposure of the monolith to sunlight causes it to emit a piercing signal that heads towards one of the moons of Jupiter. It is inferred that extra-terrestrials (who had visited Earth a long time ago before humans had evolved) had planted the monolith on the Moon to serve two purposes: Its signal would alert them to the fact that organisms on Earth had evolved to the extent that they had become advanced enough to break free of Earth’s gravitational field, and the signal’s destination would tell Earth scientists where they should go to try and make contact with the ancient visitors.

That would be an exciting possibility but alas the more prosaic explanation of a crashing meteor is likely to be the correct one. But still, maybe the scientists investigating this new blob should be alert for any signal it emits if and when it is excavated …


  1. DonDueed says

    The plot hole: there would be no way for anyone to determine where the signal was sent, unless the earth-moon system was surrounded by a mesh of detectors. There would be no reason for such a mesh to exist. The same sort of error cropped up in a couple Star Trek episodes, where some character would announce where some mysterious signal was received.

    A fun fact: in the book version of 2001, the second monolith was on Saturn’s moon Iapetus, that strange moon that’s half black and half white. But for some reason, it was spelled “Japetus”. A joke on Clarke’s part, perhaps?

  2. John Morales says


    The plot hole: there would be no way for anyone to determine where the signal was sent, unless the earth-moon system was surrounded by a mesh of detectors.

    Um, routine space travel, interplanetary ships, habitable moon bases…

    (You shouldn’t equivocate between the fictional reality and the real one)

  3. John Morales says

    PS if anything, for mine, the plot hole is the assumption of weakly-godlike aliens who uplift species. Very teleological, but subject to the usual recursive problem — the which David Brin nicely wrote about. But then, that’s the very conceit.

  4. DonDueed says

    John Morales:
    I still say it’s a plot hole. Remember that Clarke was a hard-SF guy, generally sticking to real physics. In the original short story “The Sentinel”, which was the genesis of 2001, the artifact sent a signal when disturbed but not to a specific destination. The 2001 book/movie implied that the direction of a beamed signal could be determined at the source, which simply isn’t possible.

    Within the 2001 context, the Discovery was a one-off built specially for the voyage to Jupiter (or Saturn) after the monolith did its thing. There’s no indication that there was a permanent human presence anywhere beyond the Earth-Moon system, although Mars is certainly a possibility. Even if so, there would be no need for a rather dense array of receiving stations in deep space as would be necessary to pinpoint the destination of the monolith’s signal.

    I suppose it’s possible that there were probes in the Jupiter (Saturn) system at the time just by coincidence, which might have been able to detect a signal if they happened to be designed to pick up the type and wavelength of the monolith’s beam. Even if we stipulate that, though, they couldn’t have determined that the signal only went that direction.

  5. brucegee1962 says

    I don’t get this objection. If the signal went out in a tightly-focused beam, why couldn’t you figure out where it was likely to be picked up? If you drew a line along the trajectory it was aimed at, and found that, out of all the empty space in the solar system, it just happened to hit a moon of Saturn, surely you’d assume it was aimed there?

  6. John Morales says


    There’s no indication that there was a permanent human presence anywhere beyond the Earth-Moon system […]

    Well, Pan Am spaceplanes commuted to Clavius Base, so it was clearly a commercial commonplace.

  7. says

    @brucegee1962 No. 5…

    A tight beam would work, but only if Jupiter is above the lunar horizon at that moment and Jupiter was not blocked by Earth, or the sun, and the Jovian moon targeted by the beam—I suppose a beam that tight is possible at that distance, but I have a hard time accepting that even a tight beam would indicate more than the general direction of the Jovian system—was not masked by Jupiter (or any other intervening moons or asteroids).

    That’s a lot of ifs—especially if the beam is sent the moment that sunlight strikes the monolith which mean that the monolith is facing the sun—but the beam is possible, but highly improbable.

  8. Rob Grigjanis says

    hyphenman @7: It’s been a while since I saw the movie; was the signal sent by the lunar monolith a short burst, or was the scene just cut short? It could’ve been a sustained beam, to make sure it would eventually get to its destination.

  9. Rob Grigjanis says

    John @3: I don’t see why you think that’s a plot hole. A species that advances without outside help determines that other species can be “uplifted” with a bit of a nudge. It doesn’t have to be recursive at all.

  10. flex says

    I tend to agree with DonDueed on this one. Two possibilities:

    Broad transmission -- Easy to detect the transmission occurred, but very hard to tell where it was intended to be received.
    Focused beam transmisison -- Easier to determine location of receiver, but hard to detect if you are outside the beam.

    I know, a focused beam transmission may be tens of kilometers across, but space is big. (“If you thought the walk to the chemists….”)

    My personal solution to this problem is that the movie left the response of ‘transmission received’ from the Jupiter monolith off-screen.

    In the original short story, The Sentinal, it appears to be a broad transmission. But there is no indication of where it was intended to be received. It could have been interstellar as far as the short story was concerned. Although what we know about radio wave attenuation after leaving the heliosphere suggests that simple radio frequency waves wouldn’t be sufficient. This is something a tremendous amount of SF makes a mistake about, but I’m not certain that this knowledge was available to Clarke at the time.

    I don’t recall the movie, which came out next IIRC, indicating that a response came back from Jupiter. But we do see in the movie that a tremendous amount of sensing equipment is placed around it prior to it being exposed to daylight for the first time through human action. It is possible that a focused beam transmission could have been captured. Although at that distance it may only have been a few millimeters wide. But even with sufficiently advanced technology you would want the transmitter to know that the transmission was received, that’s basic communication theory. So the Jupiter monolith could well have sent a signal back to the lunar monolith saying, “Roger”. With a dual intent of letting the lunar monolith know the message was received, and to spur the ascended apes on to Jupiter.

    Again, IIRC, the book was written while the screenplay for the movie was being written, and came out slightly after the movie. I have it down in the basement, but I can’t be sussed to look it up right now. And this is becoming a long comment anyway.

  11. Lassi Hippeläinen says

    There are two ways to create a focused beam: dish and phased array.

    The size of a dish depends on wavelength and beamwidth. The narrower the beam, the bigger the dish. A beam aimed to a small moon of any outer planet would have to be big indeed. There weren’t any big dishes in the movie.

    A phased array can be hidden inside a monolith. It can send a beam in any direction, because it only needs to control phase shifters, not physical movements like a dish. However, its nearfield can be measured, and used to compute a guess about the beam shape. The scientists digging the monolith up would have lots of instruments switched on.

    So it is “feasible” (in scifi sense) that the signal was detected.

  12. DonDueed says

    brucegee@5: A radio (or other EM) beam is invisible. Reality is not like a Star Trek phaser that shows us exactly where it’s headed. To determine where a beam of radiation goes you have to have instrumentation all around the source, so you can determine where the beam went according to which detector(s) picked it up.

    The exception would be if the transmitter was a large dish antenna and you could see where it was pointing when the signal is sent, but that wasn’t the case in 2001.

  13. DonDueed says

    flex@11: Actually my memory was a bit off. In The Sentinel there was no transmission from the device (a pyramid-shaped artifact). The first-person narrator speculates that it was sending out a signal, which humans interrupted when they destroyed the artifact. But that was just a guess — no signal was ever detected, so it must have been transmitting via some unknown technology, or perhaps at some very low duty cycle (one chirp every millennium?)

    The story may be read here:

  14. blf says

    Possibly remarkable the postulated beam — whether it was composed of EM or something else — knew precisely where the second TMA was located after many many millennia. Newton orbital mechanics could give a quite good idea, but the possibly of chaotic events — including the TMA on the Moon being exposed by one — suggests there is more going on here than is being assumed…?

  15. Steve Morrison says

    Clarke said somewhere that he picked up the spelling “Japetus” from Willy Ley, who was using the German spelling.

  16. James Stuby says

    Mass concentrations (Masscons) on the moon associated with giant impact craters have been known since 1967-68 from Doppler tracking of the Lunar Orbiter spacecraft (especially LO 4 and 5 which were in polar orbits). Others were discovered using the same technique with the Lunar Prospector spacecraft in the late 1990s, and finally GRAIL mapped them all in detail. This GRAIL map (, which is centered on the far side, shows the South Pole-Aitken basin as the blue zone near bottom center. A masscon is only faint compared to most other ones (the biggest one in upper right is in the center of Mare Imbrium). From what I have read they are caused by rebound of mantle material following the huge excavations caused by these impacts. South Pole-Aitken is bigger and older than all the other ones and its masscon may have been mostly obliterated or obsucured by subsequent impacts. Apart from being generally interesting, masscons are important because they can perturb the orbital track of spacecraft and without compensation for their effect orbiting spacecraft will crash.

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