Astronomers this week are exulting over the discovery of a planet they can't see, orbiting a star that they can't get to, at least until they find a way to travel 25 trillion miles in less than the 17,157 years it would take with existing technology. Still, the star, appropriately named Proxima Centauri, is what passes for a neighbor in our Milky Way galaxy. It is the nearest star to our solar system. And the planet, Proxima b, orbiting it, is in the so-called "habitable zone" near its sun — not so close that it's scorching, not so far that it's frigid. So it might have earthlike conditions. And that conjures the possibility of life thriving on a planet that, despite its distance, is physically closer than any other earthlike planet scientists have discovered.
Our obsession with finding intelligent life on other planets is adventuresome, practical and narcissistic all at once. We fantasize about it, make movies about it and go searching for it, with radio, optical and space telescopes, scouring cosmic haystacks for needles. And the hunt is enduring. The great 17th century astronomer Johannes Kepler wrote a science fiction novel, "Somnium," intended to describe how the Earth might look from the moon, and for that, he put living creatures there. There is an exquisite asymmetry to the question of whether there is life elsewhere in the universe. If scientists find it, then we have proven that it exists. But as Owen Gingerich, a historian of science and professor emeritus at Harvard University puts it, "if we don't find it, we can never be sure that it's not out there. No one can disprove it."
So we continue to look. And why shouldn't we? Even a failed quest to find life in our mirror image — and it's not quite clear why we think it will look like us — still enriches our knowledge of the universe we inhabit. "Finding other Earths will teach us more about our own," says astronomer Lisa Kaltenegger, director of the Carl Sagan Institute at Cornell.
And there's some encouraging news about looking for life on Proxima b. The European Extremely Large Telescope, which will be the world's largest optical telescope when construction on it is finished, should be ready by 2024 and give astronomers a sharper sense of Proxima b. And the Breakthrough Starshot initiative — a program designed to build probes capable of accelerating to 20% of the speed of light — could get a spacecraft there in 20 to 25 years. Of course, it will take at least that long to build it. But just think — once it's built, we could be there in no time at all.