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How ‘Star Wars’ worlds compare to real-life planets, according to NASA scientists

December 16, 2017

The Star Wars franchise has created some interesting worlds to tell stories.

Images of Pluto provided by the New Horizons mission reminded many planetary scientists of the frozen planet Hoth in “Return of the Jedi” (1983). Minor planet 4-Vesta has craters large enough for the Millennium Falcon to navigate through.

In 2011, NASA’s Kepler mission discovered a planet 196 light years from Earth, circling two suns. Though officially labeled Kepler-16b, even professional astronomers call it Tatooine after Luke Skywalker’s hot desert home in “Episode IV” (1977).

About the size of Saturn and with surface temperatures below -100 F, Kepler-16b lies on the outer edge of the habitability zone. Liquid water is theoretically possible, so moisture farming could be big business there, but the real Tatooine is more a gas giant than desert planet.

More recent films brought fans more familiar worlds. Jakku, depicted in “The Force Awakens” (2015) and Jedha in “Rogue One” (2016), are cold desert planets reminiscent of Mars. Cold, but habitable, the Curiosity rover last reported a high of -15F and low of -110F from its location near Mars’ equator.

“The recurring theme of desert worlds in ‘Star Wars’ is really interesting because there is some research that shows that these would be likely habitable worlds to find,” said Shawn Domagal-Goldman, an astrobiologist and climate scientists at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

If you’ve not seen “Star Wars: The Last Jedi” yet, save the rest of this article for later. While more focused on planetary geology than the movie’s plot, much of the fun of these films is experiencing the new worlds created for the audience.

Which brings us to Crait, the “mineral planet,” where the final battle scenes in “The Last Jedi” (2017) take place.

“Crait started with a very graphic idea of red underneath white, and how that could transform during the course of a battle. But the bigger idea behind it is it’s a mineral planet, and when it snows, it’s salt that’s snowing down on you, and any crevice is filled with crystals,” Director Rian Johnson said.

These scenes were filmed in Bolivia, on the world’s largest salt flats at Salar de Uyuni. These prehistoric lakes about the size of Connecticut dried up thousands of years ago. During the rainy season, a few inches of water pool on the surface creating a seemingly unending mirror that’s popular with photographers.

The salt at Salar de Uyuni is halite, NaCl (sodium chloride), your typical white table salt most familiar to us. But that’s just one type of salt.

Sylvite, KCl (potassium chloride), can be a very deep red color. It is one the last minerals to evaporate out of brine solutions and has been found under the surface of Salar de Uyuni and other salt flats, such as the Bonneville Salt Flats in Utah.

I asked Dr. Michael J. Malaska, a chemist and planetary scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California, about his thoughts on this salty “Star Wars” world.

“Halite can go dark red-brown when exposed to radiation,” Malaska said. Breaks in the crystalline structure absorb light. “I did this in the lab with a Tesla coil. It was fun,” he added.

For an analogue in our solar system, Malaska immediately points to Europa and its red-brown colorization. Europa has long thought to harbor an underground ocean. In a 2015 paper in the journal Geological Research Letters, the dark lines observed on Europa’s surface are thought to be irradiated sea salts.

A world where it rains salts onto salt flats being irradiated from below makes for a pretty cool battle field.

We’ll learn more about Crait and its place in the “Star Wars” universe in the Marvel comic book “Star Wars: The Last Jedi — Storms of Crait” set to be released on Dec. 27.