No moon likely means no tides. Does this make a planet half water, half land, or similar divisions? Do freshwater and saltwater have separation? Or would it just be a planet like ours, with delineated seas and land, but without high and low or directional tides?

I've tried to look into the question on youtube etc and only found multiple-moon speculation, without resources for moonless worlds.

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    $\begingroup$ Sun also causes tides, though its gravitational effect is smaller. $\endgroup$
    – Alexander
    Apr 11 at 20:23
  • $\begingroup$ I never knew that freshwater-saltwater separation is caused by the moon instead of the sun (evaporation, wind, precipitation). $\endgroup$ Apr 11 at 20:42
  • $\begingroup$ "No moon likely means no tides": not true. "Does this make a planet half water, half land, or similar divisions:" there is no relationship between the Moon and how much land is above the water. *"Do freshwater and saltwater have separation": no clear what this means. "Directional tides": what? $\endgroup$
    – AlexP
    Apr 11 at 22:12
  • $\begingroup$ Is this a question about whether life could evolve there, or whether humanity could move in? $\endgroup$
    – Mary
    Apr 11 at 23:41
  • $\begingroup$ Hello Jesse, welcome to Worldbuilding. For future reference: (a) asking more than one question at a time is a reason to close your question (click on "close" and read "Needs More Focus"), (b) the help center teaches us that questions "must be specific and answerable, must include context, [and] must include restrictions/requirements." You're missing all of that, which is also a reason to close a question (see "Needs Details"). In short, you should ask a single question (one question mark), explain why you're asking, and provide the scope for respondents. $\endgroup$ Apr 12 at 1:17

3 Answers 3


There will still be solar tides, assuming your planet isn't tidally locked.

However, the tides aren't the only effect of the Earth's particularly large moon.

  1. The tidal forces also drive some tectonic activity, keeping the Earth's surface alive and dynamic.
  2. The moon shields us from some asteroids and comets, particularly those near the plane of the ecliptic.
  3. The moon's orbit keeps Earth's rotational axis stable over evolutionary/geologic time periods. Without it, or with a smaller moon in proportion to our planet, the axial tilt would likely change over time, at a minimum causing large localized environmental changes.

If your planet was tidally locked, the stability problem would be solved, but habitable space would be on a narrow strip between the scorched sunward side and the frozen spaceward side. The weather would probably be routinely intolerable there, so underground habitation would be more likely. Alternatively, you could position it somewhat further away, so the habitable ring would be closer to the sunward side and with less abrupt thermal transitions/less violent weather. Similarly, it could be assumed that the cold, uninhabited spaceward side would absorb the lion's share of meteor impacts, reducing the need for the moon's protection there.

Fresh water would still be separate from salt, given similar chemistry, since fresh water is primarily precipitation that has yet to gravitate to the sea.

  • $\begingroup$ Solar tides are responsible for roughly one-third the tides on Earth, so it is no minor deal. $\endgroup$ Apr 12 at 13:53

The moon's tides helped biochemistry to develop

There's discussions about the subject, but let's put one explanation: without moon, we would not exist, or not exist yet. Without strong tides in coastal regions, certain basic biochemical processes would slow down extremely, or not occur.

we've still got a little tide left..

Probably life would slow down, not be cancelled: there will be tides: the solar tide is about half the lunar tide. So without moon, we're left with 33% of the tidal effects. The tide would occur every day, shifting over the day during the year.

shallow water zones have max tides

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In coastal zones, shallow water, the tides have max influence. Very early shallow waters may have helped primitive life-building molecules to build self-replicating structures, that is the biochemistry of early life.. pre-DNA. Found a publication in Scientific American about this,

In the early Earth environment, Lathe notes that such fast lunar tidal oscillations would result in the highly saline low-tide environment that protonucleic acid fragments would have needed to associate and assemble complementary molecular strands.

Having bonded in pairs at low tide, these newly formed molecular strands would then dissociate at high tide, when salt concentrations were reduced, providing what Lathe terms a self-replicating system. Lathe believes that DNA would ultimately have arisen from such protonucleic acids.


There could be some kind of "goldilock size" for moons. The earth as an ideal size moon for strong (meters) water tides, but limited tectonic influence. On Mars, tides from moons and sun will have been tiny, so it is doubtful if life ever emerged on Mars, it will have been slowed down irt Earth.

second wave of new life: Cambrium

Also, later on in evolution, when the Cambrian Explosion occured, higher life forms (ca 500M years before humans) thrived in shallow water zones. The abundance of calcium available in ocean water played a role there.. and the food: plant life profiting from the tides.



No Moon? No Problem.

If the moon disappeared there would be no tides. But the planet would remain habitable. The high parts are the land and the low parts are the water.

  • $\begingroup$ There would still be (smaller) tides. $\endgroup$
    – Jon Custer
    Apr 12 at 1:18
  • $\begingroup$ @JonCuster Itty bitty Solar tides. $\endgroup$
    – Daron
    Apr 12 at 12:57
  • $\begingroup$ The tidal bulge from the sun is about half that from the moon. So, tidal heights would be constant and about 1/3 of peak (sun+moon) tides. I don't consider 1/3 to be 'itty bitty'. $\endgroup$
    – Jon Custer
    Apr 12 at 13:00
  • $\begingroup$ I was trying to check that by comparing the gravitational pull of the sun vs the moon. What a silly question. Of course the sun exerts more gravity. That's why we orbit the sun and not the moon! $\endgroup$
    – Daron
    Apr 12 at 13:10
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    $\begingroup$ See oceanservice.noaa.gov/education/tutorial_tides/… for example. Note that it is the gradient, not absolute value, of the gravitational interaction that leads to tides. $\endgroup$
    – Jon Custer
    Apr 12 at 13:15

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