What If We Built a Pool On The Moon, How Would We Even Do It?

BY JOE TRUSTY

Splashing in water is a simple joy we take for granted on Earth, but what if we could experience it on the Moon? Imagine the surreal combination of weightlessness, lunar gravity, and shimmering waves beneath a domed sky. The idea, inspired by Randall Munroe’s What If? series and its episode “What if we put a pool on the Moon?”, takes a playful look at how swimming might work in an environment so unlike our own.

First, the good news: yes, you could swim on the Moon. The fundamental physics of buoyancy still apply. Buoyancy, the upward force exerted by a fluid on an object submerged in it, depends on the density of the fluid relative to the object. On Earth or the Moon, as long as you’re less dense than water (and humans are), you’ll float just fine.

In fact, swimming would feel surprisingly familiar. According to experts, the inertia of water is the main source of drag when swimming, and this property isn’t influenced by the Moon’s weaker gravity. However, the reduced gravity would create some truly unique phenomena. The lower gravitational pull (just one-sixth of Earth’s) would lead to sloshier pools, bigger waves, and the ability to leap gracefully out of the water, almost like a dolphin.

One of the most exciting aspects of a lunar pool is the enhanced physics of movement. Studies suggest that in low gravity, humans might even be able to run on water, given the right conditions. Normally, running on water is a feat reserved for small creatures like water striders or the basilisk lizard. Humans, with our greater mass and muscle limitations, simply lack the power to achieve the necessary speed on Earth.

However, researchers found that on the Moon, the reduced gravity could allow humans under 73 kilograms (160 pounds) to run on water by slapping the surface hard enough to generate lift. With some clever engineering, like special flotation devices or fins, larger individuals might also achieve this feat. Who wouldn’t want to say, “Look at me, Ma, I’m moonwalking on water”?

Here’s where the Moon pool dream takes a financial hit. A typical pool holds about 40,000 gallons, or approximately 334,000 pounds of water. Transporting materials to the Moon is astronomically expensive—around $100,000 per pound. That means just filling the pool alone could cost a mindbending $33.4 billion, never mind the cost of materials to build it. To put that price tag in perspective, we’re talking about 7.92% of Elon Musk’s entire net worth spent just to get enough water there to fill it.

Building a swimming pool on the Moon would be a fascinating but highly complex endeavor, fraught with unique logistical challenges.

One of the most immediate concerns would be creating a sealed and pressurized environment to counter the Moon’s vacuum. Without an atmosphere, water would rapidly evaporate or freeze, depending on the temperature. This would necessitate constructing an enclosure with controlled air pressure, temperature, and humidity levels to keep the water in a liquid state.

The Moon’s lower gravity, about one-sixth that of Earth, would also present challenges. The reduced gravitational pull would affect the way water behaves, causing it to splash and ripple differently. This could require innovative designs for pool containment and water circulation systems to maintain a stable and functional pool environment. Safety considerations would be paramount, as the altered

dynamics of water could pose risks to swimmers unaccustomed to such conditions.

To create a more Earth-like swimming experience, artificial gravity could be introduced through a rotating habitat. A centrifuge system could simulate gravity by spinning a section of the dome. This innovation would allow swimmers to experience more familiar water behavior, while also addressing health concerns for long-term lunar residents.

Moreover, the materials for constructing the pool must withstand the harsh lunar conditions, including extreme temperature fluctuations and high radiation levels. This would likely involve using advanced materials capable of insulating the pool and shielding it from radiation while maintaining structural integrity.

Finally, maintaining a swimming pool on the Moon would require continuous energy to power lifesupport systems, water filtration, and temperature regulation. Solar power could be a viable solution, but it would need to be stored efficiently for the lunar night, which lasts about 14 Earth days.

Building a pool on the Moon isn’t just a whimsical idea—it’s a fascinating thought experiment that challenges our engineering limits. So while the Apollo missions were all about planting flags, perhaps future Moon explorers will focus on perfecting their high dives and dolphin leaps. The day that happens will surely be one small splash for man but one giant cannonball for mankind.