Full Moon, Blue Moon, No Moon — What Would the Earth be Like if it Didn’t Have a Moon?
Last week, somebody asked me what life on Earth would be like if we didn’t have a moon.
Our moon is something we take for granted, but it’s destruction is a trope of science fiction writers. Neal Stephenson starts Seveneves by blowing up the moon. There “used” to be a moon in Richard K. Morgan’s grimdark (think gay Game of Thrones, except worse) fantasy series A Land Fit For Heroes. The Seasons in N.K. Jemisin’s award-winning The Broken Earth series were caused by the moon being put into an unstable, elliptical orbit, resulting in massive devastation each time it approached.
Of course, the destruction of the moon in A Land Fit For Heroes did nothing, but in Seveneves it results in the Earth becoming uninhabitable. The weird and very adult fantasy series The Magicians (I’ve only seen the show) has an episode where the moon is accidentally destroyed and the characters have to prevent the same event.
Destroying the moon would almost certainly end all life on Earth. But what if the Earth had never had one in the first place? Needless to say, this isn’t explored as much in science fiction, and there’s a peculiar tendency to assume inhabited planets have some kind of moon.
So, what would our planet be like if it didn’t have an unusually large moon?
Tides Would be Quite Different
No moon = no tides? Not quite.
The lunar tide is the strongest, and we are used to it, and this tends to result in the assumption that if we never had a moon, there would be no tides.
Not so fast!
We actually have two tidal influences on the Earth. One is the moon, which has the stronger influence because it’s close.
The other is, drumroll, the sun.
The sun is why we have spring tides; they happen when the sun, moon, and Earth line up and the sun and moon are both pulling in the same direction. The rest of the time, the sun and moon work at cross purposes.
Tides would probably be about a third of what they are now…less dramatic but still enough to create a tidal zone. However, the people on our hypothetical moon-less Earth would probably never have invented surfing.
Our Days Would Be Shorter
Over time, the gravitational influence of the moon has lengthened the Earth’s day. This is still happening; days are slowly, very slowly, getting longer. It’s by like 1/75000 seconds a year, so nothing we need to worry about for timekeeping.
Without the moon, days would be quite a bit shorter. Life on the planet would, of course, have evolved to that timescale. We wouldn’t really know we had shorter days.
(If you’re creating an alien world without a moon, feel free to give it whatever length of day you want).
Nights Would Be Much Darker
Even a new moon gives off a tiny bit of light. Think about the difference between a full and new moon…if you’ve been camping when the moon is full you may even have been able to leave your tent in the middle of the night without a flashlight.
Without a moon, nights would be much darker, although we might be able to see more stars.
This might have affected how our vision evolved, and it’s likely that more nocturnal animals would rely on echolocation rather than sight.
Seasons Would Be Unstable
Climate change is bad enough, but on a world with no moon, climate change would be a normal thing to which species…and civilizations…would have to adapt.
The moon stabilizes the Earth’s axial tilt. Without it, the planet would wobble more.
The axial tilt would vary over a shorter period. Instead of having ice ages and interglacials, such a world would literally have epoches where parts of it never saw daylight, and then ones where there were no seasons at all.
How fast this would happen would likely depend on how your planet was constructed. You could envision people living in a stable period, but they would likely know that things were going to change again eventually.
Folklore Would Be Different
Think about how much we include the Moon in our folklore and fairy tales. There would be no cow jumping over it, no “Man in the Moon.” No lunar deities.
No association of women’s cycles with…well…who knows. We might not even cycle on the same pattern.
Without the moon we would have to invent other things in the sky to see as important and sacred. Of course, with a much darker night sky maybe we would see other things, like nebulae, that could become the “home of the gods.”
I don’t buy the idea that intelligent life couldn’t evolve on a world without a moon. But they may well be jealous of ours, especially if their climate changes a lot.
Thankfully, our moon is here to stay, certain novels aside. Or is it?
The moon is slowly moving away from the Earth. Will the moon leave us?
It’s moving away so slowly that the sun will expand into a red giant and eat both worlds long before that. Which we don’t have to worry about for 5 billion years.
(However, in about 600 million years the moon will be far enough away that we won’t ever get another cool solar eclipse to watch. Catch them while they last!)
Our moon definitely affects our life and how we evolved, but it’s fascinating to imagine a world without it.
And a very dark sky.