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  • Writer's pictureM.C.

Alien Megastructures

As the James Webb Telescope joins the Hubble and earth-bound radio telescopes in the search for alien life, what might they find? Considering the distances to even the closest star systems, only the largest structures–those whose gravity may affect orbits, whose energy output can be identified, or whose bulk may dim the visual light of their star–may be found. 

In other words, only the most massive of alien megastructures.

But this area isn’t totally unknown, as science fiction authors and scientists alike have wondered what types of structures alien civilizations might need. Massive structures may be needed to capture the energy requirements of a space-faring race. Or massive orbital platforms may be created as colonies expand from a homeworld.

This list encompasses a variety of imagined megastructures that may exist somewhere in our galaxy:

  • Dyson Sphere/Dyson Swarm - An artificial structure in the form of a hollow shell surrounding a star, built to capture the star’s energy output as a stellar engine (see below) or as a habitat. Where a Dyson Sphere imagines a solid object encompassing a star and capturing all possible energy, there would be issues with habitation due to a lack of gravity (the Shell Theorem), or if spinning to produce gravity, a gravitational gradient that would lessen to zero at the rotational poles. A Dyson Swarm focuses more on energy capture as a loose collection or swarm of objects that either only partially encompass the star, like a net, or travel on independent orbits around the star. (Star Trek:The Next Generation episode “Relics” imagines a Dyson Sphere.)

  • Niven Ring - Representing only a single band encircling a star, a Niven Ring would provide both energy capture and habitation. If set at a distance equal to Earth’s orbit the inner surface would be entirely habitable with an atmosphere that would remain gravitationally attached. It could also rotate to provide artificial gravity 99% as strong as Earth's from centrifugal force. (Larry Niven’s Ringworld series imagines life on such a construct.)

  • Bishop Ring - Similar to but much smaller than a Niven Ring, a Bishop Ring would not encircle a star but orbit one. It would still be large enough to be built without a "roof" as the atmosphere would be retained by artificial gravity and atmosphere retention walls on either side. The habitat would be oriented with its axis of rotation perpendicular to the star, with either an arrangement of mirrors to reflect sunlight onto the inner rim or an artificial light source in the middle. A Bishop Ring could exist in its own orbit around a star or in a planetary LaGrange point for stability. (The video game Halo represents a series of Bishop Rings.) 

  • Alderson Disk - A giant platter with a thickness of several thousand miles where a star rests in a hole at the center of the disk. The hole would be surrounded by a thousand-mile-high wall to prevent the atmosphere from drifting into the star while the outer rim would not require a wall. Life could exist on either side of the disk, though only a ring roughly equivalent to Earth’s orbit +/- 5% would be habitable by humans. (Malibu Comics’ series Godwheel imagined such a disk where technology ruled one side and magic the other.)

  • O’Neill Cylinder - Consisting of two enormous cylinders divided into solid sections for habitation and farming and windowed sections for light and energy. The two cylinders would rotate in opposite directions to cancel any gyroscopic effects that would destabilize the structure’s orbit. Each cylinder would be connected at the end via a rod and bearing system. Their rotation would provide artificial gravity while large mirrors hinged at the back of each strip of window points toward the star. They could also exist in their own solar orbit, a planetary LaGrange point, or planetary orbit. As enclosed structures, O’Neill cylinders would require an immense life-support system. (Both Murphy Station in the movie Interstellar and the titular station in Babylon 5 are O’Neill Cylinders.)

  • Stanford Torus - A torus, or a doughnut-shaped ring, that is connected via a series of spokes to a centralized hub. The entire structure would rotate, providing artificial gravity along the inside of the outer ring while the hub would have no gravity. Sunlight would be provided to the interior of the torus by a system of mirrors, including a large non-rotating primary solar mirror. The spokes serve as conduits for people and materials traveling to and from the hub. Since the hub is at the rotational axis of the station, it experiences the least artificial gravity and is the easiest location for spacecraft to dock. (Space Station V in 2001: A Space Odyssey consists of two connected tori on a single hub.)

  • Space Station - Though defined as a spacecraft which remains in orbit and hosts humans for extended periods of time, such as the current International Space Station, a space station identifying an alien civilization would be of massive proportions. It may also be in planetary orbit or stabilized in a planetary LaGrange point. (Most notable examples are from the Star Trek universe, including Starbase 1 which orbits Earth and Deep Space 9 which sits in a LaGrange point near Bajor.)

  • Space Elevator - More of a connector/transport to a megastructure than a structure itself, it connects an orbiting platform with the planet below. A tether would extend from the surface to a counterweight in space beyond geostationary orbit. The competing forces of gravity, which is stronger at the lower end, and the upward centrifugal force, which is stronger at the upper end, would result in the tether being held under tension, and stationary over a single position on Earth. With the tether deployed, climbers (crawlers) could repeatedly climb up and down the tether by mechanical means, releasing their cargo to and from orbit. (The Star Bridge in Asimov’s Foundation connects the orbiting space dock to the surface of Trantor.)

  • Stellar Engines - A class of hypothetical megastructures which use the resources of a star to generate available work (or, in other words, to generate energy). They can use the energy of the star to produce mechanical, electrical or chemical work or they can use the impulse of the light emitted by the star to produce thrust. For example, Matrioshka brains have been proposed to extract energy for computation, while Shkadov thrusters would extract energy for propulsion. 

How would you feel if the James Webb Telescope actually identified one of these structures on a faraway planet? Let me know in the comments.


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