By Mark Alpert
This was an epic week for science-fiction fans, a week when real-life scientists validated one of the most cherished sci-fi legends. A pair of astronomers at Caltech revealed strong evidence for the existence of Planet X, the long-rumored world lurking at the edge of our solar system.
The quest for Planet X started more than a hundred years ago. At the time, astronomers believed that the gravity of a distant, unseen body was disturbing the orbits of Neptune and Uranus, pulling the planets out of their predicted paths. The search for this body led to the discovery of Pluto in 1930, but its mass was too small to account for the theorized gravitational effects, so astronomers continued to peer at the heavens through their telescopes, hunting for large planets far from the sun. In the 1980s, the Voyager 2 spacecraft whizzed past Uranus and Neptune, giving scientists a much better measurement of the planets’ masses; these results changed the astronomers’ predictions for the paths of the outermost planets, and now they lined up with the telescopic observations. There were no unexplained gravitational disturbances in their orbits after all, and hence no need for a Planet X.
In the meantime, though, science-fiction writers had already brought the mysterious world to life. Planet X appeared in countless novels and short stories. Jules Verne called it Olympus. Arthur C. Clarke called it Persephone. Robert Heinlein called it Kalki. Roald Dahl called it Vermes (home of the Vermicious knids). It was as if the astronomers had handed the authors a gigantic blank canvas on which they could scribble their most outrageous fantasies. That’s the essence of science fiction: it’s a team effort. Scientists supply the fuel — the inspiration — and build the launch pad. Writers plot the course and fire the rockets.
And the grand thing about science is that it’s always churning up new mysteries from the cosmic muck. As soon as one question is answered, a deeper, more difficult question takes its place. Starting in 1992, astronomers equipped with more powerful telescopes started detecting hundreds of smallish bodies similar to Pluto, occupying a broad belt of space beyond Neptune’s orbit, between three billion and five billion miles from the sun. It was dubbed the Kuiper Belt, after Dutch-American astronomer Gerard Kuiper. Then, in 2005, a team led by Caltech astronomer Michael Brown discovered a Kuiper Belt object that was more massive then Pluto. Named Eris, after the Greek goddess of strife, the newly detected body presented astronomers with a semantic problem: if they called Pluto a planet, then Eris had to be considered a planet too, not to mention dozens of other Pluto-size objects that hadn’t been discovered yet because they were so far away. The International Astronomical Union didn’t want so many planets in our solar system, so they changed the definition of the term: a planet, the IAU ruled, has to be massive enough to gravitationally clear its orbital region of all other bodies. Under this definition, our solar system has only eight planets. Pluto was demoted to the humbling status of “dwarf planet,” sharing the new designation with Eris and thousands of Kuiper Belt objects and asteroids.
There was a huge outcry over Pluto’s demotion, but Brown was unapologetic. In the years afterward, he wrote a book titled How I Killed Pluto and Why It Had It Coming. He also kept studying the mess of objects beyond Neptune. He was particularly intrigued by a dwarf planet called Sedna, which he discovered in 2003 and named after an Inuit goddess of the sea. Sedna travels in a wildly eccentric orbit that goes way past the Kuiper Belt, ranging between seven billion and 90 billion miles from the sun. In recent years, astronomers have discovered several other dwarf planets with similarly far-flung orbits, and oddly enough, all their trajectories seem to be oriented the same way: the points of the orbits farthest from the sun (the aphelia, in astro lingo) are clustered in the same part of the solar system. Brown and his Caltech colleague Konstantin Batygin calculated that the odds of this happening by chance are only 1 in 14,000. They also concluded that the most likely cause of this cosmic coincidence is the gravitational pull of a distant Planet X.
But are they right? Is Planet X real, or will it turn out to be a mirage again? Unlike earlier astronomers, Brown and Batygin have powerful computer modeling tools that show how a large planet could pull smaller bodies out of the Kuiper Belt and fling them into crazy orbits like Sedna’s. But the planet would have to be massive — as much as fifteen times the mass of Earth, or almost as heavy as Neptune — and it would have to orbit through the farthest reaches of the solar system, perhaps ranging more than 100 billion miles from the sun. The Caltech astronomers are already looking for the planet using the Subaru Telescope at Mauna Kea Observatory in Hawaii. If they find it, the solar system would go back to having nine planets, because Planet X would definitely be big enough to meet the new definition.
Amazing discoveries like this are the perfect starting point for fiction. I came up with the idea for my upcoming sci-fi thriller, The Orion Plan, while I was editing a special issue of Scientific American about space exploration. I’ve always been fascinated by the possibility of interstellar travel, so I assigned the esteemed science journalist Timothy Ferris to write about the subject. (For the full article, see “Interstellar Spaceflight: Can We Travel to Other Stars?”) Ferris argued that the fundamental challenge of interstellar travel is that the stars are so enormously far apart. Even the 100-billion-mile distance between our sun and the putative Planet X is less than half of one percent of the distance between the sun and the nearest star. Sending a huge spacecraft like the Starship Enterprise to another star system would be completely impractical because it would take so much energy to accelerate the craft to a significant fraction of light speed. The effort would probably bankrupt even the most advanced civilization.
But sending a small spacecraft — say, a probe about the size of a bowling ball — just might be feasible. And if the probe is packed with advanced electronics and artificial intelligence and automated tools, it could establish a firm foothold on whatever planet it lands on. Its automated tools could dig into the rock and soil at its landing site and use the local minerals and metals to fashion solar panels and a small manufacturing facility, which could in turn produce everything needed to explore the planet: rovers, drones, rockets, even self-replicated copies of the probe. This, I thought, is a very cool idea. And it was a little scary too, because the same tools could be used to colonize the planet. I started to wonder what would happen if a small automated probe from another star system landed in my hometown.
The Orion Plan will be published by Thomas Dunne Books/St. Martin’s Press next month, and Bookspan — which runs the Book-of-the-Month Club — has chosen the thriller to be one of the selections for its Science Fiction Book Club. I want to talk some more about how I wrote the novel, but I’ve already gone on too long, so I’ll continue the story in my next blog post two weeks from now.
Speaking of sci-fi, my science thriller for young adults — The Six — has been named a finalist for the 2015 Cybils Awards in the Young Adult Speculative Fiction category. And if you read that book and enjoyed it, please recommend The Six to be nominated for the Andre Norton Award given by the Science Fiction and Fantasy Writers of America (SFWA). Just send an email to firstname.lastname@example.org and mention The Six by Mark Alpert. I’d really appreciate it!