How plausible are the planets in Star Wars?

On the volcanic planet Mustafar, Anakin duels with Jedi Master Obi-Wan Kenobi, ends up nearly submerged in lava, and must turn into a cyborg to survive. What kinds of forces would cause a planet to form like that? What would we need to survive?

Tikoo-Schantz: Such a volcanic planet can exist from tidal heating. A comparable world would be Jupiter’s moon Io, which gets flexed on the inside by the gravitational pull of Jupiter and other Jovian moons. The resulting stress releases a lot of heat. However, the gases in the atmosphere of such a volcanic world would be noxious and surface temperatures would likely be too hot for anything to survive, much less get in a fight.

Schaefer: We have also found some exoplanets that orbit their stars so closely that they have permanent dayside magma oceans. But as Sonia said, the temperatures are so hot that you’d burn to a crisp before you got to have your Jedi duel.

The icy planet Hoth hosts a temporary Rebel base where the heroes have to defeat Imperial walkers in order to escape. How would you explore the snow-covered orb? What subsurface processes form a rocky vs. icy planet?

Schroeder: Ice-penetrating radar would be the ideal geophysical technique for exploring Hoth. It would allow Rebel Alliance scientists and engineers to determine the thickness and properties of Hothian ice and snow. This would be useful for creating icy infrastructure like fortifications and ice-roads that avoid or exploit crevasses as well as for investigating the climate and history of the planet itself.

In terms of platforms, you could do a global survey from space if you had enough power (probably not a problem for a spacecraft with the power to approach light speed), unless snow-processes on Hoth produce problematic clutter reflections for the radar. Rebel airspeeders travel too fast to be an ideal airborne platform for ice-penetrating radar, so you’d probably go orbital for large-scale surveys and then tauntaun-pulled sleds for very local fine-scale studies.

Lapôtre: Because icy worlds form far from their host star(s) where temperature is low, ice essentially behaves like rock. At depth, viscous ice may convect like Earth’s mantle, leading to some kind of tectonics and even forming reservoirs of “magma” which create volcanoes when the magma finds its way to the surface. At the surface of planets without giant atmospheres, the ice is really cold and behaves like granite on Earth. On Titan, for example, rivers of methane and ethane erode a crust of water-ice rock.

Hoth, in contrast with the icy worlds of our solar system, is not technically an icy planet—it is a rocky planet covered in snow and ice. In that sense, it is more analogous to Snowball Earth, when our own planet was entirely frozen. This happened a few times in Earth’s history, through a runaway process in which an increasing snow cover led to more and more of the sunlight being reflected back to space, leading to further cooling. The last Snowball Earth episode is thought to have happened just before the explosive diversification of life in the oceans.

After escaping Hoth, Han Solo attempts to navigate an asteroid field that surrounds the planet, eventually landing on one of the rocks, which they discover is home to a giant space slug. Is this what asteroid fields are really like? What happens when they hit the surface of Hoth? Could an asteroid support life?

Tikoo-Schantz: This scene is totally unrealistic. Asteroids are not even remotely close enough to each other for a spacecraft like the Millennium Falcon to have to dodge around them. The average distance between two asteroids in our asteroid belt is 600,000 miles! If you flew in a random straight line through the asteroid belt, you are almost certain to NOT hit anything at all.

I looked up the “canon” description for this asteroid field and it says that it was formed by the collision of two rocky planets. In reality, these types of planetary collisions primarily happen at the beginning of a solar system’s lifetime, and the resulting debris would have either come together to re-form a new planet or be gravitationally perturbed and ejected to other parts of the solar system.

Our asteroid belt is made up of many, many planetesimals that were gravitationally “herded” into their current position—mostly by the gravitational forcing of giant planets like Jupiter—and is not related to the breakup of a single planetary body. But if the Star Wars asteroid field was real, the objects hitting Hoth would vaporize upon impact. If these impacts are large enough or occur frequently enough, they could pose a serious threat to life forms living on Hoth.

Schaefer: An asteroid would be an unlikely place to find life, especially giant space slugs. The largest object in our own asteroid belt (Ceres, now classified as a dwarf planet) is only 7% the size of Earth and about the size of Texas. Its gravity is much too low to allow it to hold onto an atmosphere, which is vital to make liquid water stable at the surface.

Tiny bacteria could possibly survive in the subsurface brines of Ceres (if they somehow managed the space journey to get there), but it’s unlikely they would thrive and evolve into a large organism because the environment is so inhospitable and energy-limited.

Microscopic tardigrades (also known as waterbears) on Earth are possibly the only multicellular animal that could survive such conditions (again, if they somehow got delivered there), but they would be in a dormant hibernation state, and also not likely to evolve into a giant space slug.

The heroes in Star Wars embark on many solo missions to other planets, as well as large-scale efforts to move the entire Rebel fleet to new operation bases. What goes into space missions from Earth? How have you been involved?

Schroeder: Space missions that we organize from Earth include hundreds of people. They play a wide range of roles from science and engineering to management and leadership. Planetary missions take years to decades to develop and operate. As a science team member on the REASON instrument (Radar for Europa Assessment and Sounding: Ocean to Near Surface) on NASA’s upcoming Europa Clipper Mission, I’ve had an opportunity to help with the requirements, design, and scientific planning for the instrument. Once the mission arrives at Europa, we’ll use the radar data to investigate the geophysical processes and potential habitability of the moon’s ice shell.

Lapôtre: I was a science team member for the Curiosity rover that is currently investigating an ancient lake environment on Mars. I participated in daily operations with hundreds of other scientists and engineers, and had the opportunity to lead the rover’s investigation of a modern dune field. On a daily basis, we would all convene by teleconference to discuss the latest data sent back to Earth, and decide where to go next before the engineers implement our plan and send instructions to Mars. With so many scientists on the team, it can be very difficult to get the rover to go where you want it to—you have to make a pretty compelling case to convince others your idea has more merit than theirs!

In one of the most iconic scenes from the original Star Wars movie, Luke Skywalker walks outside his uncle’s moisture farm to gaze at two suns on the horizon of his home planet of Tatooine. What makes it possible for a planet to orbit two stars? What do we know about binary systems in the universe?

Schaefer: About half of all stars like the sun are actually in binary systems. We have currently found 143 planets in 97 binary systems. In 22 of these systems, the planets orbit both stars, but in the remaining systems, the planets orbit only one of the stars in the system. In most of these binary systems, one of the stars is often much bigger than the other, so having two stars that are about the same size is a little unusual.

Most of these systems also seem to be coplanar: The planets and the stars all orbit in the same plane, indicating that they formed from the same protoplanetary disk. To make two stars, the disk would have had to be much more massive than the protoplanetary disk for a single-star system, but otherwise the process of planet formation would work much the same way as it does for other systems, except that planets that formed too close to the binary pair might end up being ejected from the system. Planets far enough away from the binary pair have stable orbits and may be habitable.

What has been the most exciting discovery you’ve witnessed since you started your research in planetary sciences?

Lapôtre: To name just a few of my favorites, I’d say (1) the diverse landscapes of Pluto, with mountains, glaciers, plains, and even possibly dunes; (2) the active migration of ripples at the surface of the 67P/Churyumov Gerasimenko comet; a comet has no atmosphere, and as such, the formation of ripples, let alone the detection of their motion during a short-lived mission, was very surprising and exciting; (3) the discovery of a type of Martian ripples that does not exist on Earth; (4) the possible detection of a subglacial lake beneath Mars’ polar cap.

Tikoo-Schantz: One thing that really excites me is that new developments in technology have enabled us to study the physical and chemical properties of extremely small samples of extraterrestrial materials (even things that are less than a tenth of a millimeter across) and learn about large-scale processes that were going on in the early solar system. For example, we can retrieve paleomagnetic records from individual chondrules (tiny spherules that are some of the first solid materials in the solar system) and learn about magnetic fields that were present in the disk of gas and dust that orbited the protosun before the planets formed. But perhaps the thing that most excites me is the discoveries we are making in other solar systems.

Schaefer: The variety of exoplanets discovered around other stars continues to astonish me. We don’t have examples of the most common types of planets (super-Earths and sub-Neptunes) in our own solar system, suggesting that our home system is unusual—not just for hosting life. There have also been amazing new observations of proto-planetary disks around other stars showing gaps in the disks where we think large planets like Jupiter are forming: This level of detail had never been seen before until the last 7-10 years with the ALMA telescope and is really starting to change the way we think about planet formation.

How has Star Wars influenced your ideas, aspirations, or career choices?

Tikoo-Schantz: I am a lifelong science fiction nerd. As a kid, all of the “Stars” (Star Wars, Star Trek, Stargate) presented me with this vision of a universe filled with innumerable worlds waiting to be explored and a sense that we are not alone on our little blue dot in space. A great motivator for me as a planetary scientist is the idea that perhaps someday I will be able to fact-check some of these fantastical planets I read about via my research and see whether or not aspects of these worlds could exist in reality.

Schroeder: In academic science, as in any career, you encounter people, processes, and cultures doing things out of “anger, fear, or aggression” (which, as Yoda explains, belong to the “Dark Side” of the force). Star Wars is a good reminder to do our best to keep things like this out of science; to appreciate rather than tear down the work of our colleagues, to work on projects because of intrinsic interest instead of a fear that others may do them first, and to reject the temptation to keep a record of real or perceived scholarly slights. Star Wars challenges us to be Science Jedi not Science Sith.