Readers of this blog know that I’m a big fan of Quora, because it lets non-experts raise the kinds of speculative questions that don’t normally come up in formal scientific discussions. One frequent theme that comes up is the issue of what we would do if we found intelligent life on a planet around another star. A recent posting in particular caught my eye: “What would we do if we found an Earthlike planet with intelligent life that is 500 years behind us in technology and advancements?”
Well, that’s a fun thought experiment! It’s not one question, really, but a whole set of nested questions about how to find alien life, how to determine the presence of alien intelligence, how to determine the nature of that intelligence, and then how we would study it, or even try to make contact with it. There’s a big moral issue at the end, but a lot of juicy scientific ones along the way. And that got me thinking…
First, how will we find a truly Earthlike planet?
Despite all the amazing recent discoveries of planets around other stars, astronomers have yet to find a true Earth twin — that is, an Earth-size planet orbiting a sunlike yellow star at an Earthlike distance. The closest they’ve come is a planet called Kepler 452b. It’s roughly five times the mass of Earth and probably belongs to the class of planets called super-Earths. Habitable, maybe; Earthlike, no. The same goes, even more so, for the recently discovered Earth-size planets around the star Trappist-1. These are extremely exciting worlds to study, and it is possible that some of them could support life. But the Trappist-1 planets orbit a dim red-dwarf star, which means that they are blasted with energetic radiation and are probably tidally locked, with one hemisphere always facing toward the star.
