Suppose we have an Earthlike planet, with a rocky moon orbiting it. Under what conditions would dark lunar maria form on its surface, and would they always be on the side facing the planet? For Earth’s Moon, it appears that the maria face the Earth due to heat radiating from the molten Earth. How universal is this phenomenon? Does it depend on, for example:

  • Whether the moon was formed in an impact, or if it was captured?

  • The size of the moon, from the smallest rocky body that forms a sphere under its own gravity, to being the equal to the size of the planet (a double planet)?

  • The presence of gas giants in the solar system? (It seems Earth’s Moon got its maria from asteroid bombardments caused by Jupiter and Saturn.)

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    $\begingroup$ There is no scientific consensus regarding the reasons for the peculiar distribution of Lunar seas. From the Wikipedia article on Lunar maria: "the reason that the mare basalts are predominantly located on the near-side hemisphere of the Moon is still being debated by the scientific community". The same article list a series of common misconceptions about Lunar seas. $\endgroup$
    – AlexP
    Commented Jan 14, 2018 at 20:47
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    $\begingroup$ This is more a question for Astronomy SE that Worldbuilding. There's no worldbuilding here. $\endgroup$ Commented Jan 14, 2018 at 21:40
  • $\begingroup$ "For Earth’s Moon, it appears that the maria face the Earth due to heat radiating from the molten Earth." As was pointed out earlier, this is nonsense. The maria and craters we see now came much later than Earth and the Moon solidified. Also Maria don't stem from bombardment. They're volcanic in origin. $\endgroup$ Commented Jan 14, 2018 at 22:24
  • $\begingroup$ @AtmosphericPrisonEscape Explaining that, with references, would likely be the correct answer, then. $\endgroup$
    – kingledion
    Commented Jan 14, 2018 at 22:59
  • $\begingroup$ @kingledion: That's also on the wiki page AlexP linked. $\endgroup$ Commented Jan 14, 2018 at 23:42

1 Answer 1


We see the maria of the Moon because the moon is tidally locked with the Earth. It is a theory that the near side and far side appear so different because the far side has taken so many more hits from space debris than the more sheltered nearside.

  • $\begingroup$ Welcome to WorldBuilding blueworld! If you have a moment please take the tour and visit the help center to learn more about the site. Have fun! $\endgroup$
    – Secespitus
    Commented Jan 29, 2018 at 8:34

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