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No matter how advanced our civilization here on Earth becomes, there’s a sobering fact we have no choice but to reckon with: Earth’s resources are finite. That not only includes the resources we typically think of, like minerals, clean water, and breathable air, but also something even more fundamental and restrictive: land area. No matter how thoroughly we develop, there’s only a finite amount of continental land area to inhabit on our planet.
While “floating cities” on the seas and oceans may someday become a possibility, the finite surface area of planet Earth ensures that, beyond a certain point, we’ll need to leave our home planet if we want our civilization to continue to grow. Although many of us have dreamed of living on another world, we have yet to find even a hint of life on a world beyond Earth, much less a fully inhabited planet or one habitable by humans. If we want a world to be suitable for us to live on, it looks like our only option will be to transform a presently uninhabitable planet into one that humans can survive on — a process called terraforming. Despite the popular sentiment that Mars is the right world to terraform within our solar system, there may be an even better option closer to home: the Moon. Here’s the science of why.
Four theoretical phases of terraforming that would take Mars from the red, desolate planet it is today (top left) to a world where life sustained and thrived, very similar to Earth (lower right). Although this is an ambitious dream, terraforming the Moon might prove much easier. ( Credit : Daein Ballard/Wikimedia Commons)
At first glance, it might appear that Mars is much better suited for terraforming than the Moon. After all, Mars already has large quantities of water on it: in both the solid and gaseous phases. Mars had a past where liquid water was rife on the surface, and probably spent more than the first billion years of its existence with oceans and rivers throughout its surface. Mars is larger and more massive than the Moon; it has a higher gravitational acceleration than the Moon does at its surface; and its atmosphere, while thin, is rich in carbon dioxide.