The Science (& Fiction) of Star Wars: Part 2

by Sam Atkins

Let’s explore some more things from the Star Wars universe and how they relate to real astronomical concepts.

NOTE: Tap or hover over images for captions and credits.

Is the Death Star a Practical Weapon?

Image credit: Disney

The very first Star Wars movie introduced the iconic Death Star. It’s a 160 km-wide spherical space station that houses over a million imperial crew members including military, technicians and droids. It famously features a superlaser capable of blowing up entire planets. Is it cool? Undeniably. Is it practical? Nah.

Let’s put aside the physics, logistics and economics of building a moon-sized battle station. The energy required to blow up an Earth-sized planet, meaning to obliterate it until gravity can’t hold it together, is astounding. You’d need the equivalent of a 50 quadrillion megaton bomb. For comparison, the Chicxulub asteroid that wiped out the dinosaurs delivered about 100 million megatons of energy. That means you would need the force of roughly 500 million Chicxulub impacts (by the way, you can check out my article on Chicxulub here). This is more energy than the Sun emits in an entire week. Even if you could somehow harness that much energy, it would need to be delivered very quickly and precisely, or else the planet would otherwise radiate it away. A laser, even with that amount of power, is unlikely to penetrate deep enough and overcome its gravity. Earth is just too big and the laser would get scattered away before reaching the planet’s core.

In the Star Wars universe, the Death Star’s superlaser is powered by kyber crystals, Force-sensitive minerals that channel and amplify energy with extreme efficiency. This is the same resource that powers the even-more-iconic lightsabers. Other sci-fi universes offer more science-grounded ways to harness planet-destroying power. Still, you could argue that blowing up a planet is overkill. If you want to deal with a pesky rebel planet, there is a much simpler solution: throw a giant asteroid at it. A 20 km-wide rock at a hypervelocity would devastate the entire surface of a planet. The main benefit here is that you might actually be able to commandeer the planet for yourself later. The energy cost to redirect an asteroid is microscopic compared to the Death Star. Heck, throw a couple of asteroids if you really want to be sure. Many sci-fi stories have used this method before like Mass Effect and The Expanse. Alternatively, you could drop giant tungsten rods from orbit and let the planet’s gravity do the rest like in G.I. Joe: Retaliation.

Disclaimer: Do not blow up planets. It’s mean and politically inflammatory.

Forest Moons

Image credit: Disney

In the original Star Wars trilogy, we see two instances of moons that have Earth-like environments. Episode IV: A New Hope has Yavin 4, the site of a rebel base being targeted by the Death Star, while Episode VI: Return of the Jedi has Endor, the site of the shield generator for the second Death Star. Both of these moons are a far cry from the barren, airless cratered worlds we usually think of in our own solar system. Instead, they have breathable atmospheres, rich vegetation and even intelligent native creatures like the Ewoks. But could moons like this really exist? Well, we haven’t found any out in space yet. In fact, we haven’t identified any exomoons at all. Granted, we’ve barely been able to look. Humans have sampled the space equivalent of a glass of water from all the world’s oceans. Distant star systems are difficult to study, but as we develop better technology we may be able to get intimate looks at planetary systems. The James Webb Space Telescope might even be the first to do so!

In the meantime, there’s at least one moon in our solar system that breaks the pattern: Titan, the largest moon of Saturn. It has a thick, nitrogen-rich atmosphere, surface lakes and rivers of liquid methane and ethane, and even experiences rainfall. It also has a regular day-night cycle. Titan is tidally locked to Saturn so each day would last as long as its 16-hour orbit. The problem is that Titan is incredibly cold and its chemistry is not compatible with Earth life. For Titan to resemble the forest moons in Star Wars, Saturn would need to orbit in the Sun’s habitable zone so that liquid water could be supported. That’s not too big of an ask. We’ve found tons of gas giants around other stars in their habitable zones. Also, the tidal forces of the gas giant stretching the moon’s interior could help maintain the world’s heat should they be a bit further out.

Titan would also require a significant change to its chemistry. Its methane and hydrocarbons, which are toxic and block sunlight, would need to be replaced with oxygen to support respiration, as well as carbon dioxide for photosynthesis and greenhouse warming. Water vapor would also be needed to sustain a water cycle and help regulate the climate. Interestingly, Titan might already have a subsurface ocean of liquid water trapped beneath its icy crust that could be tapped for such a purpose.

So, while moons like Endor and Yavin 4 are science fiction for now, there’s nothing in physics that rules them out. Earth-like moons could exist under the right conditions, but they might be very rare.

Faster-Than-Light Travel

Image credit: Disney

In the Star Wars universe, as in countless other works of science fiction, human civilization has spread far from its home world to the stars beyond.

The space between stars is more tremendous than you can probably comprehend. If the Voyager 1 space probe were heading in the right direction, it would take more than 75,000 years to reach the next closest star, Proxima Centauri. To travel from one side of the Milky Way galaxy to the other would take Voyager 1 about 3,885 times the current age of the universe. For humans to travel between stars in reasonable time periods, science fiction employs advanced technology that allows them to travel faster than light, often several times faster. Is this possible? Could we really do this in the future?

Well, the hard answer is we don’t know. The harder answer is it might not be physically possible. It has to do with special relativity. In 1905, Albert Einstein declared that the speed of light is the same for everyone, no matter how fast they’re moving. If you are standing still, light moves at 300,000 km/s relative to you. If someone else is moving, light still moves at 300,000 km/s relative to them. That means that light can move at two different speeds, simultaneously. How is this possible? Time slows for the person who is moving and the faster they move, the slower time passes. This is known as time dilation and it is a very real phenomenon that we have observed and measured.

Another thing that happens as you move faster is your mass increases. But moving mass requires energy. If your mass increases with speed, the energy you require to continue accelerating increases too. This goes all the way to the speed of light where an infinite amount of energy is required. This is not possible in our universe. Thus, no object with mass can reach the speed of light, let alone exceed it. Furthermore, to move faster than light would mean you could arrive at a destination before you left. This would be a clear violation of the principle of cause and effect, creating a paradox that no known laws of the universe can sanction.

In other words, faster-than-light travel is not just hard, it breaks the laws of physics as we currently understand them. Perhaps one day we will come to a new understanding of physics that does allow it, but until then, it remains in the realm of science fiction. We’re stuck in this solar system.