If It Hadn’t Been for the Moon’s Formation, Would the Earth Have Become a Super-Earth?

Many aspects make life on our planet possible, but would Earth still be a paradise if it hadn’t been for the collision that created our Moon?

Artist's depiction of the Mars-sized planet Theia colliding with the young Earth. The collision is thought to have created the Moon; Source: Wikipedia

The Earth is the biggest of the terrestrial planets in our Solar System, and yet it’s fairly small. A look at the terrestrial exoplanets scientists have discovered so far reveals that a certain type of planet exists that we don’t have in the Solar System.

Enter Super-Earths. 

Super-Earths are terrestrial planets intermediate in size between Earth and the next biggest planet in the Solar System, Neptune—right at the verge where planets go from rocky to gaseous. Some Super-Earths that we know of can be twice as big or even bigger than our own Earth. 

About 30% of the roughly 5000 known exoplanets are Super-Earths. So why don’t we have one at home?

A look at our own planet and its moon may provide an answer. When you look at the other rocky planets—Mercury, Venus, Mars—you find that they don’t have moons, except for Mars, but Phobos and Deimos are thought to be captured asteroids from the asteroid belt. 

The Earth and its Moon are therefore unique. 

Astronomers are quite certain that the Moon is the result of a giant impact between our Earth and a Mars-sized planet early in its formation, when life hadn’t even developed yet. That collision tore part of our planet apart, forming what would become the Moon. 

This means that Earth must have been bigger before the Moon formed. So what if this collision had never happened? What if the Earth would still be its initial size, orbited by nothing but a few occasional asteroids captured in its billions of orbits around the Sun?

The Moon orbits the biggest rocky planet of the Solar System, and the Moon itself counts as one of the biggest natural satellites in the entire Solar System; Source: Wikipedia

We can truly be thankful for the Moon’s existence—being the next-closest celestial neighbor, it has influenced cultures and mythology for millennia; whether that be legends about the full moon or the fact that Earth is the only lucky planet in the Solar System to experience solar eclipses. 

The Moon affects not only life on Earth, but also the planet itself. 

The gravitational forces exerted from the Moon to Earth result in ocean tides, and thanks to the Moon we have a stable rotation speed. 

But we already see the effects of the Moon’s distance slowly increasing to Earth. Every year, the average length of day increases by 17 microseconds—that may not sound like a lot, but in thousands or millions of years, one day will last considerably longer than now. 

That said, the Moon is an important stabilizer to our planet and the life it harbors. 

If our Moon had never been formed, a lot would be different now. Quite literally, Earth would be a totally different planet. We can’t know exactly how big Earth would be if it hadn’t been for the impact; but let’s assume that Earth would be double in size, making it essentially a Super-Earth. 

With an Earth twice its size, surface gravity would significantly increase. If life were to exist, it would be small, as the increased gravity would make it impossible for larger animals or trees to stand upright. 

Or perhaps this Super-Earth would be covered in one large ocean.

Artist's depiction of a Hycean world; Source: Wikipedia

Astronomers believe that Super-Earth ocean worlds exist out there; specifically Hycean planets. These are Super-Earths with a global water ocean beneath a thick hydrogen atmosphere. 

In comparison to Earth, these oceans reach far deeper and constitute a significant part of the planet’s mass—and wherever you look from a point-of-view of the surface, you see water. 

While a global ocean may seem like a haven for life, Super-Earth oceans would come with so many side-effects that no life could ever thrive there. If this ocean sits beneath a thick atmosphere—as is hypothesized for Hycean planets—water vapor would eventually lead to a runaway greenhouse effect, causing the ocean to evaporate. 

However, a Super-Earth doesn’t have to be uninhabitable. Smaller life forms could thrive despite the intense gravity on a world that carries the ideal balance between landmass and ocean. 

And researchers have suggested that Super-Earths could hold on to warmth better at greater distances from their stars, extending the habitable zone around a star. 

A Super-Earth version of our planet would alter things forever. And we wouldn’t be here if it weren’t for the violent collision that created the Moon, to put it dramatically. 

The planet we were given is a unique world—and every month, when the full moon illuminates the night sky, remember that it is thanks to this cosmic entity that a peaceful life on Earth is possible. 

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