Dr Abalone

When I first saw the giant waves in the latest Star Wars movie, Rise of Skywalker, it took my breath away. Massive, huge and slow-moving, they were the perfect menacing grey-green monsters to create a barrier to the ruins of the second Death Star and the location of a Sith Wayfinder. But the Falcon crashed, so how was Rey to cross the giant surf? With a skimmer of course. And within minutes, we see a woman raised on a desert planet skillfully riding a skimmer through massive swells, deftly navigating the giant waves. Real or fantasy? How big were those waves? Could a small moon of the planet Endor create such surf? Let’s check it out.

Endor System

First, we have to calculate the gravity on Kef Bir as that influences wave height. The planet Endor is located in a binary star system in the Moddell sector of the galaxy’s Outer Rim Territories, an area rife with hyperspace anomalies. Endor itself is a gas giant with nine moons. One of the moons is the forested moon, also called Endor, where the Battle of Endor was fought in Return of the Jedi. One of the other satellites is the ocean moon Kef Bir. The forest moon’s diameter was 4900 km, 70% the size of Mars. However, the forest moon supposedly had a lighter-than-standard gravity (Wallace and Fry, 2000). The diameter of Kef Bir itself is either 3,725 km (Wookiepedia, Star Wars) or about 4,000 km based on the size of the Death Star 2’s impact in the surface (Bressar, 2020); or about half the size of Mars (6,792 km). With that diameter, if the mass was similar to Mars, the gravity on Kef Bir would be greatly reduced, about 20% of Earth’s.

This is both interesting and important as it is 30% smaller than the planet Thalassa in my book, Songs of Thalassa, which features monster waves at a surf break called Colossus. The waves on Kef Bir looked exactly how I pictured Colossus in my mind, which is why the scene was so stunning. See, waves on low-g planets are super cool, which is why I used them in my novel, because oceanographic theory predicts waves should be bigger and move significantly slower than on Earth.

Waves on Mars

Believe it or not the theory is derived from Mars’s oceans. If you went back 3-4 billion years Mars had an ocean, Oceanus Borealis, that covered about a third of the planet with an average depth of 450 feet (137 m). Research by Dr. John Banfield at Cornell and his colleagues (Banfield et al., 2015) demonstrated that wind blowing across the surface of that ocean produced wind waves, just like on Earth.

But what would the waves have looked like? According to Banfield (and see Choir, 2015)  they were likely large and moved significantly slower when compared to Earth. Since Mars has only 10.7% of the mass of the Earth its gravitational field is only 38% of Earth’s so it is easier to generate large ocean waves. However, gravity also acts to push waves along and determine their speed. Thus less gravity also means slower waves. Since Kef Bir’s gravity was only 20% of Earth’s the waves would have been even bigger. Check these babies out to see what I mean. How big do you think they are?

Waves on Kef Bir

To find out I did some frame grabs of the wave where Rey rode her Skimmer up a wave’s face (I subscribe to Disney+) and I applied a little math. First I calculated the size of the skimmer relative to Rey:

With Rey at 5’6” I calculated the length of the skimmer to be 20 feet (9.1m). Then I calculated the size of the wave as she went up the face using three frame grabs by comparing the wave size to the skimmer size.

The challenging part is locating the bottom of the wave. If you looks closely there is a smaller wave building in front of the Rey’s wave but I ignored that and focused on the main wave. After measuring three wave heights, the average estimated wave size was 287 ft. (87m). Yikes, yeah. But hold your horses as we’re not done yet. Because we are looking down on the wave it appears larger than it actually is as we are looking at the slope of the wave, not it’s height. Assuming a viewing angle of 20° and applying a little trigonometry the average estimated wave size is 260 ft. (79m)!

Yes, that’s unreal, and much bigger than the largest wave ever surfed on Earth, currently set by Rodrigo Coxa at Nazaré 2017 at 80. ft. Importantly, the size is consistent with what you would expect on the low-g planet of Kef Bir so Disney got it right (although the team should have been bouncing up and down like John Carter on Mars).

What about Thalassa? Yes, the whole reason it is a low-g planet, 20% smaller than Mars, to create a setting for massive waves and the big-wave surf off between Sage (the main character) and her nemesis Milo.. To find out how big the waves are on Thalassa, you’ll have to read the book but they are pretty big.

Rey in the Waves

As to Rey riding giant waves; is that possible? Because she was raised on the desert planet Jakku it is unlikely she had any experience with waves or oceans. So Kef Bir was probably her first encounter with big waves. Could she have realistically ridden those waves with the skill she showed in Rise of Skywalker? Of course, because she’s a badass Jedi and the Force is with her.

References

• Banfield, D., M. Donelan and L. Cavleri. 2015. Winds, waves and shorelines from ancient martian seas. Icarus: 368-383.
• Bressan, David. 2020. The Death Star Crashing On A Planet Would Have Caused A Dinosaur-Sized Extinction Event. Forbes.
• Choi, C. Q. 2015. Ancient Mars May Have Had Slow-moving Monster Waves. Space.com Retrieved Dec. 9, 2015.
• Iijima, Y., K. Goto, K. Minoura, G. Komatsu and F. Imamura. 2014. Hydrodynamics of impact-induced tsunami over the Martian Ocean. Planetary and Space Science 95: 33-3
• Kef Bir, Wookieepedia, the Star Wars Wiki. Accessed May 6, 2020
• Nasa, 2015. NASA Research Suggests Mars Once Had More Water Than Earth’s Arctic Ocean. Nasa.gov
• Surfing on Mars, Dr. Abalone
• Wallace, D. and J. Fry. 2009. Star Wars: The Essential Atlas. Del Rey Books. 256 pp.