Astronomers discover a new world for us to conquer.
ASTRONOMERS HAVE DETECTED A NEARBY PLANET WITH AT LEAST 1.3 TIMES THE MASS OF OURS.
Aplanet with Earthlike temperatures around the nearest star in the night sky. This seems almost suspicious, l ike a hint that the world was created by a pulp science fiction novelist. Yet it appears to have come to pass. And I, in turn, feel that in discussing this news with you, I might be a Heinlein or an Asimov, writing fake news to drop into the first act of a galaxy-colonization epic.
Thursday, astronomers and other scientists working on the Pale Red Dot project announced t hat they have detected a planet with at least 1.3 times the mass of ours. It is orbiting the red dwarf star Proxima Centauri, which is a little more than four light- years away. This distance is no bagatelle, but it is reachable within one lifetime by means of propulsion technology we can imagine building now. We do not need to i magine “wormholes” or some other improbable physics frammis to provide travel above light speed.
The scholars behind the Pale Red Dot plan, funded by the consortium of European states that operate t he European Southern Observatory in the Chilean desert, do not disguise that they have been influenced by the priorities and the romance of science fiction. The idea was to search for exoplanets i n our neighbourhood, among the lowintensity, small stars that provide the easiest readings for new planet-searching instruments.
At interstellar distances, exoplanets cannot simply be photographed. Their existence has to be inferred by watching their parent stars wobble as they orbit them. ( I meant to make that sentence longer and fanciersounding, but I cannot see anything that needs adding to it.) Planets pull stars toward us as they are approaching from one side, and they pull them away from us on the other. They, in short, create a wobble.
If we “stare” at a star long enough using very sensitive spectroscopic instruments, we can detect the periodicity of a planet- caused wobble from the to- and- fro Doppler effect of the light f rom the star. Starlight, or anything else’s light, is shifted toward the red end of the spectrum as it moves away from us ( you probably learned in school that the universe is flying apart and that good old Edwin Hubble discovered this by noticing that “redshift” was pervasive among very distant heavenly objects). Light is also shifted in the other direction, toward violet, when an object emitting l i ght comes toward us. HARPS, the High- Accuracy Radial Velocity Planet Searcher that bagged the new planet, dubbed Proxima b, can detect spectrum shifts so small that they represent movement of as little as a metre per second.
So the limits of our detecting instruments create the conditions for optimum radial- velocity detection of exoplanets: the planet needs to be big enough relative to the star to make it wobble, so smaller, cooler stars are preferable. Proxima is only 12 per cent as massive as our Sun; its “effective temperature” ( I’ ll have to let you Wikipedia that one) is on the order of 3,000 degrees kelvin, which you could produce briefly in your backyard if you laid hands on some thermite. But Proxima b is whipping around the star Proxima at just onetwentieth of the distance between the Earth and the Sun; its orbital period is all of 11 days.
To me, much of the marvel of scientific developments like this is the grandeur of the inferences that can be made from small scraps of data. That was my experience of studying astronomy in university as a non- science major: the instructor would take one parameter, scribble some pis or lambdas on an overhead projector, and it seemed to take only a moment before he was telling us, with an authority we had to accept if we were following the math, what kind of yam would grow best on Venus.
The Pale Red Dot investigators, as I say, do not have anything like a traditional photograph of Proxima b, or even an artist’s impression. What they have is a spike on a chart that recurs every 11 days — a ( magnificently constructed) statistical abstraction. But it is enough i nformation for them to dive into a discussion of biological habitability (“Tidal locking does not preclude a stable atmosphere”) and even speculate on the origins of Proxima b (“pebble migration would produce much drier worlds”).
The philosopher Auguste Comte, knowing how far away the stars really were but unaware of spectroscopy, wrote in 1842 that we may be able to see extrasolar bodies move, “but we can never know anything of their chemical or mineralogical structure, and, much less, that of organized beings living on their surface.” The joke was on him: the history of spectroscopy was already well under way, and its astronomical use was only a few years off. As for the “organized beings,” who knows? In the long run, they may be us.