We shall not cease from exploration
And the end of all our exploring
Will be to arrive where we started
And know the place for the first time.TS Eliot, Little Gidding
Some people feel a need to explore. I share their wanderlust. I believe it is fundamentally healthy, and possibly critical for our long-term survival as a species that some of us feel this way. It’s not about abandoning the Earth in its time of need. It’s not ‘either/or,’ but ‘both/and’. Perhaps we can better care for our planet by a few of us leaving it, and thereby learning how to better care for one another in the cold and dark of outer space. By attempting to grow a new civilization on Mars, we might come to appreciate more fully the fragility of the one we have here on Earth.
Astronauts have written about such emotional epiphanies, and the keen poignancy of seeing the Earth from space. We’ve sent machines to other planets and hopefully one day soon, we’ll send more people not only to the Moon, but on to Mars and the asteroids. Building what is sometimes called a ‘spacefaring’ civilization in our solar system seems possible, though it will be hard, the work of centuries.
But the stars might remain out of reach for humans. Why? Are we thinking of sending unmanned probes, or people? Trips lasting a single human lifetime, or centuries? That’s the crux of the matter.
Chemical rockets are limited by basic physics to speeds that imply by using them, it will always take nearly a decade for even small payloads to reach the Outer Solar System. The so-called ‘interplanetary superhighway‘ is, in fact, quite slow, since it seeks to exploit not the fastest orbits between solar system objects, but those orbits requiring the least expenditure of fuel. On the interplanetary superhighway, all things come to those who wait.
Nuclear rockets, or fusion powered systems, might reduce the transit time to the outer solar system by an order of magnitude at best over chemical rockets. For example, some estimates suggest they can reduce the Earth-Mars transit time from eight months to three. But, a very rough figure to keep in mind is that the solar system is about a light-day across, while the nearest stars are light-years distant. Proxima Centauri, the nearest star, is thus thousands of times more distant that Pluto, implying thousands or tens of thousands of years travel time using currently available technologies. The most distant human-built object is Voyager 1, launched in the late 1970’s to explore the outer solar system, is heading out to the stars, one of the fastest objects ever created by human ingenuity. And yet it is still, after all this time, less than one light-day from Earth.
An old cliché holds that nothing is impossible for those who don’t have to do it themselves. So, while we might imagine the building of what are called ‘generation starships’ in science fiction, these would have to be city-scale craft with sizable crews sufficient for settlement on the other end. These crews might sleep out the centuries of travel in some form of stasis, a technology we currently don’t posses. Or if not asleep, they would be born, grow old, and die in transit, knowing that they are en route from an Earth they know of only in histories, toward a future they did not choose. These ideas, if taken up and examined seriously, present not only serious technological and ecological challenges, but ethical questions as well. This is the theme of Kim Stanley Robison’s dystopian novel Aurora.
We might instead ask about sending our machines. This is more achievable if we hope to reach the nearest stars on human time scales. Then, instead of rockets carrying humans we might imagine other possibilities, such as using ground-based lasers to propel light-sails with far smaller space probes, barely larger than a fingernail. In principle, if such high-powered lasers could be built and focused for many months on small light-sail targets leaving the outer solar system, probes could achieve much higher speeds than rockets and in principle reach the nearest star – Alpha Centauri — in a few decades of travel time.
These novel forms of propulsion are much less developed, and will require decades of development, but they are still based upon known physics. Sending extremely small machines to the stars in a human lifetime therefore might be doable, though it’s far beyond current capabilities. Even wilder schemes based on new physics, of course, might be discovered in coming centuries. We can always hope. And that’s precisely the point. I believe it’s healthy for us to imagine what future generations might accomplish if our generation manages to navigate our current sea of troubles. To wonder if our descendants might, in fact, have a destiny out in the wider galaxy.
But, it’s also true that we’ll never find our way to the stars if we first lose our way on Earth. Given all that’s at stake, and all the problems we face every day, should we still aspire to go to the stars? Doesn’t it seem presumptuous, or even a little deluded? Perhaps, but I don’t think so. I think we should look up and dream big dreams of a human future that is more humane and hopeful. And then, like TS Eliot said all those years ago, through our wanderings, perhaps we’ll come to know ourselves for the first time.
The text is licensed under a Creative Commons Attribution-NoDerivatives 4.0 International License.
Image: This artist’s impression shows a view of the surface of the planet Proxima b orbiting the red dwarf star Proxima Centauri, the closest star to the Solar System. The double star Alpha Centauri AB also appears in the image to the upper-right of Proxima itself. Proxima b is a little more massive than the Earth and orbits in the habitable zone around Proxima Centauri, where the temperature is suitable for liquid water to exist on its surface. Source: https://www.eso.org/public/images/eso1629a/. Shared under a Creative Commons Attribution 4.0 Copyright.