How Many Planets Can You Fit Between Earth and Moon?

Inspiration

Inspiration for this page came when I was watching Scott Manley’s live stream of Kerbal Space Program. Someone asked — can you fit all the planets of Solar System in space between the Earth and Moon? I thought it was a really good question to answer.

Later I discovered that there was an infographic on reddit claiming it is possible. Also, I’ve found that Fraiser Cain from Universe Today also answered the question in his blog post. But they got it wrong and here is why.

Assumptions

The question “How Many Planets Can You Fit Between Earth and Moon?” has different answers depending on your assumptions. To make everything clear, here are the assumptions I used.

First, the Earth-Moon distance. The distance varies between 363 104 km when the Moon is closest to the Earth and 405 696 km at its furthest distance. The average distance between the Earth and Moon, which is also known as lunar distance, is 384 400 km.

But, the lunar distance is a distance from the center of the Earth to the center of the Moon. This is the point at which everyone else made a mistake. I needed the average distance Earth-Moon from surface to surface, so I needed to subtract the radius of the Earth (6371 km) and radius of the Moon (1737 km). Hence, the distance used on the page is 376 292 km.

Next, I assume we are stacking planets by the equatorial axis (so that the planets are on the same plane) and that planets are perfect spheres with their mean radius. These are very important assumptions for answering our question. Thanks to rotation the planets are a bit more squeezed on the polar axis, making the equatorial radius a bit bigger than the polar radius. If you stack the planets on the polar axis you can easily fit all of the planets in our Earth-Moon distance and still have some room left. In that case, the sum of planets’ circumference will be 364 799 km — a bit more than the Earth-Moon distance when the Moon is at the closest position.

Lastly, I excluded Pluto from the list of planets (Pluto is a special, complicated case) and assume we are adding Saturn without its rings.

How was it made?

For this page, I decided to use React with Flux. I just wanted to learn it and see what the fuss all about. The best way was to build something in it.

The design went through a couple rounds of refinement. The thing that changed the most was the buttons to add or remove planets. They went from being on the right side to an experiment with circular navigation to land finally when they are. Circular navigation was a cool looking idea, but it sucked in terms of usability.

In the first version of the page, you could only add one planet of its type. You were allowed to add only one Mars, one Jupiter, and so on. But after first round of feedback I’ve decided to allow to add as many planets as you can.