Diving into Lunar Waters: The Surprising Reality of a Moon-Based Swimming Pool!

A fresh video from xkcd cartoonist, science educator, and writer Randall Munroe has raised the classic inquiry; what if we placed a pool on the Moon?

While enjoying a splash in water on Earth is pleasurable, it appears that if NASA accelerated their efforts, it could become significantly more entertaining.

To start, would it be feasible to swim in it? Buoyancy is an upward force present in a fluid (any flowing material, including air) acting on all objects immersed within it. This force originates from the pressure within the liquid becoming greater the deeper beneath the surface you go. The pressure acting on the bottom of an object submerged in the fluid exceeds that at its top, resulting in the upward force. If the buoyant force of a fluid surpasses the weight of an object placed within it, then the object will float. This principle holds true on the Moon as well, and since astronauts have a lower density than water, they would float effortlessly in the Moon pool.

Swimming would also feel quite similar, as Munroe indicates that the inertia of water is the primary cause of drag while swimming, a characteristic that is not influenced by the gravitational setting you find yourself in. What makes it particularly fascinating is that the reduced gravity results in a sloshier pool, larger waves, and the chance to leap out of the water akin to dolphins. Which, I believe we can all agree, is what the Apollo Moon missions lacked.

Another intriguing element mentioned in the video is the possibility of astronauts running on the pool’s surface. A 2012 study examined how various (small) animals manage to run on water. While water striders utilize surface tension to remain afloat, larger creatures such as the Basilisk lizard must rely on the more energy-consuming method of propelling themselves off the surface of the water “with sufficient vigor to generate hydrodynamic forces on their driving legs to support their weight”.

Humans possess considerably more weight, making this method nearly impossible, at least here on Earth.

“Humans would only be able to run on water if they could strike the surface at velocities >30 m/s [98 feet per second], which they estimate would demand around 15 times a human’s available muscular power,” the researchers mention in their study. “Nonetheless, there are two strategies to bypass these constraints. One approach is by lowering gravity, while the other involves running with flotation devices (large shoes or fins) similar to those outlined by Leonardo da Vinci.”

Calculating the numbers and conducting low-gravity tests on Earth, the researchers discovered that with a stride frequency of 1.7 strides per second, it would be plausible for humans to run on water on the Moon, up to a weight capacity of 73 kilograms (160 pounds). While “one small step for man, one giant leap for mankind” was impressive, perhaps one day we’ll hear the far more exhilarating “look at me, Ma, I’m a pond-skimmer”.