How Humans Will Finally Reach Interstellar Space

This article originally appeared on Motherboard.

Editor's note: This is a companion piece to the science fiction short "Dark was the night, and cold the ground," published Thursday in Terraform.

As the summer of 1977 drew to a close, twin siblings bid farewell to Earth to explore the ultimate frontier. They wrote back often, and sent lots of beautiful postcards, so that everyone at home could keep up with their adventures. Each of them carried an identical golden time capsule, filled with the sights and sounds of the world they left behind, so they could act as ambassadors to any other lifeforms they might encounter on their endless journey.

Now, 40 years after they were launched, Voyager 1 and 2 have traveled farther from Earth than any objects made by humans. By capitalizing on a rare orbital alignment, they were able to visit all four gas giants in the solar system—Jupiter, Saturn, Uranus, and Neptune—between the two of them, sending back some of the most iconic views of those worlds ever captured.

In August 2012, Voyager 1 entered interstellar space, our first emissary ever to do so, and Voyager 2 is expected to join the 12-billion-mile-high club within the next few years. Both probes are nearing the end of their operational lifespans, and will be switched off during the 2020s. After that, they will sail away from our solar system into the medium between stars, forever, unless they encounter something—or someone—that stops them.

In Miguel Fernández-Flores' short story "Dark was the night, and cold the ground," published Thursday in Terraform, that "someone" is a crew that includes two humans and a talking hermaphrodite chicken. Set in 2177, 200 years after the launch of the Voyagers, the story follows a novelty mission from Earth to intercept these old relics of early spaceflight, which have since been outclassed by much faster ships capable of reaching other galaxies.

As the first mission to literally reach for the stars, the spacecraft will always be the trailblazers for any interstellar trips that follow them, including the much-hyped Breakthrough Starshot mission concept announced in 2016 by physicist Stephen Hawking and billionaire Yuri Milner.

Hawking and Milner's plan is to shoot lasers at a fleet of "StarChip" nanocraft—tiny computer chips attached to light-sensitive sails—to propel them to Alpha Centauri star system. But while Starshot is delightfully futuristic, it cannot transport humans. As the Sun slowly loses its grip on the Voyagers, this raises the question: When will humans be able to follow these pioneering spacecraft to distant stars?

The answer may well be never, but that's no fun. There is no lack of creativity about devising potential avenues for humans to fly beyond our solar nest. For instance, the wormhole option, which appears in everything from the 2014 film Interstellar to Rick and Morty, is a perennial favorite for science fiction creators, probably because it has a deus ex machina ease to it.

Instead of laboring over ways to transport our delicate meatbag bodies over light-year distances, wormholes, which are speculative connections in spacetime between two distant points, act as cosmic shortcuts to the stars. The idea of faster-than-light drives, like the one depicted in Battlestar Galactica, is another close cousin of the wormhole. But it's not known whether these phenomena even exist, let alone if they could be harnessed to make an interstellar subway system.

In other words, we may be stuck with the scenic route. But even with that limitation, there are hundreds of speculative concepts for interstellar passenger spacecraft floating around, across a wide spectrum of technical feasibility.

Sleeper ships could contain crews placed in some form of suspended animation during the journey, which would reduce the need for bulky life support equipment. Generation ships would be designed to nourish living human colonies for centuries, or even millennia, once they are in transit from Earth to another star system. Seed ships could be entirely robotic, but might contain human embryos that could be delivered to distant star systems where they would be incubated and, presumably, raised by robo-caretakers.

Each of these options represents massive engineering challenges that are not likely to be resolved in an average 20th century lifespan. But as Fernández-Flores alludes to in his story, life expectancy in the 21st and 22nd centuries could conceivably skyrocket to true Methuselah levels. This prediction, along with the story's nods to transhumanism (and transchickenism), gets at the meatiest question entangled with the dream of human civilization on an interstellar dimension: Who, exactly, will these post-Sun humans be?

The space philosopher Frank White , author of The Overview Effect : Space Exploration and Human Evolution, uses the term homo spaciens to refer to the deviation of Earthbound humans into many spacefaring species, which would become adapted to life in space or on alien planets. An example would be the belters of The Expanse book and television franchise, who are so accustomed to life outside strong gravity wells that they cannot return to Earth without experiencing "gravity torture."

The term homo spaciens powerfully emphasizes the reality of interstellar human travel as an inevitable evolutionary rift. Humans may one day embark on missions to other stars, but it doesn't necessarily follow that the lifeforms that arrive on those frontiers will be human. Aside from the genetic drift that would occur on a cosmic scale, the cultural values of a spacefaring civilization are likely to wildly differ from those of a strictly terrestrial one.

With astonishing foresight, the creators of the Voyager probes anticipated the need to preserve pre-interstellar human culture 40 years ago, which is why the two spacecraft bear identical copies of the Golden Record, phonographs packed with "115 images in analog format, greetings in different languages, and 90 minutes worth of soundscapes" as Fernández-Flores describes them.

The Voyager Program is the rare exploratory expedition that seeks not only to define humanity's surroundings in the universe, but to explicitly define who we are, as Earthlings. Even after the Voyagers disappear into radio silence, the encoded memories of our planet and its people will range far beyond our home system. Maybe there will a come a time when an alien species recovers these rich snapshots of a small blue planet orbiting an average yellow dwarf star. Maybe, as Fernández-Flores suggests, that alien species will be us.