By Mark Alpert
It was another glorious week for science fiction fans. A Russian billionaire teamed up with two of Earth’s greatest living physicists — Stephen Hawking and Freeman Dyson — to start a project called Breakthrough Starshot, an effort to send a fleet of space probes to Alpha Centauri, the system of three stars closest to our sun. (The two larger stars, Alpha Centauri A and Alpha Centauri B, are a binary pair that revolve around each other; the smaller third star, Proxima Centauri, orbits the pair at a distance.)
The new interstellar project is still very much in the planning stage, and though the Russian philanthropist Yuri Milner committed $100 million of his Internet fortune to the effort, that’s just a tiny percentage of what an interstellar mission would cost if it ever got off the ground. Still, the announcement stirred the hearts of sci-fi enthusiasts who have long gazed yearningly at Alpha Centauri, which is a mere four light-years from Earth. (Actually, the three-star system is in the southern sky, so if you live north of Florida you can never see it at all. But I think you get my drift.)
Remember Lost in Space, that silly TV show from the 1960s? Well, before the Jupiter 2 got thrown off-course by the dastardly Dr. Smith (“Oh, the pain! The pain!”), the intrepid space-faring Robinson family was headed for Alpha Centauri. And surely you remember Avatar, the blockbuster film that featured the blue humanoid creatures of the planet Pandora? That planet was also in the Alpha Centauri system, where it competed for orbital space with Cybertron, the original home of the Transformers.
I guess it’s the relative closeness of Alpha Centauri that makes it a favorite setting for science-fiction writers. (The next-closest system is Barnard’s Star, which is about six light-years away.) But Alpha Centauri is close to us ONLY in the relative sense. Four light-years is equal to about 25 trillion miles. NASA has sent five spacecraft beyond the orbits of the farthest known planets in our solar system, and the fastest probe (Voyager 1) is now streaking through interstellar space at almost 40,000 miles per hour, but even at that rate it would take more than 70,000 years to reach Alpha Centauri (if the probe were actually headed in that direction, which it isn’t).
Is it possible to send a spacecraft to Alpha Centauri in a less ridiculous amount of time — say, less than fifty years? Is there any chance that our children or grandchildren will see close-up pictures of the planets (if there are any) orbiting those stars? I examined this question in detail in a blog post I wrote for Scientific American earlier this week, but here’s the short answer: it’s possible if the spacecraft is small and light enough. To reach Alpha Centauri in twenty years, the probe must speed through interstellar space at more than 100 million miles per hour, and it’s a lot easier to accelerate a penny-sized spacecraft to that velocity than it is to propel a big, manned spaceship like the Jupiter 2.That’s just common sense.
And this brings me back to science fiction. My latest novel, The Orion Plan, features an alien space probe so small and inconspicuous that when it lands in Inwood Hill Park in New York City, the only person who notices it is one of the homeless alcoholics who sleep on the park’s wooded hillsides. This kind of alien invasion seemed less farfetched to me than an attack by gargantuan spaceships. And it also seemed spookier.
So I was pleased to hear Stephen Hawking and Freeman Dyson talking this week about employing the same kind of strategy for our own interstellar missions. Whatever the extraterrestrials can do, we can do better.