I have some friends claiming that the moon is an artificial satellite, put in place recently. (I've already read the Is the moon young? question.)

Apart from the age, the usual "evidence" given by YouTube videos and sites includes:

  1. The Moon has a lower density than the Earth (3.3 g/cm^3 vs 5.5 g/cm^3), so it must be hollow
  2. The Moon is perfectly round; it is not flattened along the axis from pole to pole like the Earth
  3. Impact craters are convex, due to a more metallic layer just under the surface dust
  4. Given these "facts", the Moon must be a an artificial hollow metal shielding covered with dust

Has this "evidence" been debunked? Is the Moon an artificial spaceship?

A couple of articles they refer to:

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    Please don't crosspost on multiple stackexchange sites. When you changed your opinion about which stackexchange site fits best, either delete your question and repost it, or ask a moderator to migrate the question by flagging it for moderator attention. – Philipp Jan 9 '16 at 16:20
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    @AlessandroDaRugna - There will always be claims that cannot be proven wrong to the satisfaction of the claimant. For example, you can't prove that your friends don't have invisible dragons in their garage. Any evidence you provide will be challenged with some other baseless, but scientific-sounding claim. As Carl Sagan said, "extraordinary claims require extraordinary evidence," and none has been provided. You have no obligation to waste your time disproving ludicrously absurd claims. – Mark Jan 9 '16 at 17:56
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    The Earth is a bit flat at the poles due to it's spin rate. The moon spins much slower, of course there's much less flattening. – Loren Pechtel Jan 9 '16 at 20:01
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    @AlessandroDaRugna-So do you mean to say that those sites claim of a current artificial satellite moon having a hollow metal shielding covered with dust replacing the natural satellite moon viewed by the Babylonian astronomers in 5th century BC and Chinese astronomers in 4th century BC who have calculated lunar eclipses on basis of such a planetary object? – pericles316 Jan 11 '16 at 10:13
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    That's no moon; it's a space station. /ducks – Piskvor left the building Jan 12 '16 at 10:36

This slide from a University of Tennessee astronomy course discusses five "serious" theories of the moon's formation, and concludes:

At present the fifth hypothesis, that the Moon was formed from a ring of matter ejected by collision of a large object with the Earth, is the favored hypothesis; however, the question is not completely settled and many details remain to the accounted for.

In particular, it dismisses some of the other theories as conflicting with evidence collected from the moon:

A detailed comparison of the properties of Lunar and Earth rock samples has placed very strong constraints on the possible validity of these hypotheses. For example, if the Moon came from material that once made up the Earth, then Lunar and Terrestrial rocks should be much more similar in composition than if the Moon was formed somewhere else and only later was captured by the Earth.

These analyses indicate that the abundances of elements in Lunar and Terrestrial material are sufficiently different to make it unlikely that the Moon formed directly from the Earth.

Such a conclusion would also eliminate the conjecture posed in the question.

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    Wasn't there a recent article that matched the structure of moon rocks to the internal structure of really old sediment bedding and found a match? Can't find it offhand, but... – Shadur Jan 11 '16 at 13:41
  • @Shadur that would be very interesting to read! – Alessandro Da Rugna Jan 11 '16 at 20:26
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    @AlessandroDaRugna Found it: wired.com/2012/03/moon-formation-collision – Shadur Jan 11 '16 at 21:05

In addition to @hadriens good answer (+1):

(i) Many forms of rock appear to have a density of about 3g/cm^3 (see e.g. here), so a density of about 3.3 g/cm^3 certainly does not imply that the moon is hollow, it could simply be made of solid rock. I would suggest that the Earth is more dense because, unlike the moon, it has an iron core (iron has a density of about 7.8 g.cm^3).

(ii) The moon is not perfectly round, its polar radius is 1736.0 km, but its equitiorial radius is about 1738.1km. It is more closely spherical than the Earth, but that isn't surprising as its rotational period is about 27 days, which is much slower than that of the Earth, so the centrifugal force is lower (although so is the gravitational force, which would make it easier for the moon to become more oblate). The flattening of the Earth is 0.0033528 and that of the moon is 0.0012, so the Earth is three times more oblate than the moon, but then again it is spinning nearly thirty times faster.

(iii) Apparently, some very large craters have convex floors, simply because the convexity follows the curvature of the moon, so unless some clarification is provided, this argument may simply be a misunderstanding.

(iv) This is a non-sequitur from (i) to (iii) as none of those actually imply that the moon is necessarily hollow or artificial. (i) and (ii) are very weak arguments, as very basic fact checking shows that there is nothing unduly suprising in either of these "facts".

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  • It shouldn't be difficult to say roughly how much the flattening should be based on density and size (ignoring surface tension of course, that would be very difficult). – yo' Jan 13 '16 at 22:12
  • However, such calculations are not permissible on SkepticsSE. – Dikran Marsupial Jan 14 '16 at 7:54

put in place recently.

This is untrue.

Note, I am treating "put in place" as different from say "destroyed and replaced". It implies there was previously nothing similar in orbit about the Earth.

enter image description here Lunar drawing by astronomer Thomas Harriot, possibly the first recorded observation using a telescope, dated 26 July 1609. (c) Lord Egremont.

1609 is not recent (using the word as might be expected by the general public).

Also there are very old records of observations of the moon

Around 400BC, Aristotle deduced that the Earth was round from the shape of the Eath's shadow on the Moon during a lunar eclipse.

About 200BC, Hipparcos carried out a calculation of the dimensions of the Earth-Moon system.

History of moon observation

There is evidence of lunar observations many thousands of years BCE.

It is probable that there were two major megalithic lunar observatories ain the Carnac area.

Megalithic Lunar Observatories

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