The Worlds of the Galaxy

The Milky Way is Teeming with Exoplanets

I remember a LONG time ago, when I first got interested in science fiction as a kid, the idea of planets around other stars came completely naturally to me. Science fiction will do that — present situations that are so alien and unknown to us — and then, a few years later, we find some of those situations in real life. Like exoplanets. SF writers mostly made them Earth-like since it’s easier for humans of the future to explore them. Sure, there were some worlds where ammonia-breathing monsters chowed down on methane-ice maidens, but for the most part, the worlds of the SF future were variations on Earth.

In the search for extrasolar planets, astronomers have concentrated first on just finding them around other stars. That takes a lot of time. Two spacecraft — the Kepler andCOROT missions —were dedicated to exploring small areas of sky very minutely. Their discoveries made it possible to declare the confirmed existence of 167 planets, plus more than 3,500 planet “candidates”. The image  to the left shows all those worlds lined up by size.

The Kepler team just announced the discovery of 833 new candidate planets, with at least ten of them existing in their star’s habitable zones.  (The habitable zone is the range of distance from a star where the surface temperature of an orbiting planet may be suitable for liquid water). These ten also have masses almost two times Earth’s. Those are good attributes to focus on if you’re looking for worlds that might have life on them.

The real kicker from the Kepler discoveries that, if you extrapolate these findings out to the night sky, most of them have at least one planet. In fact, after extensive analysis of Kepler data, it turns out that one in five stars will have a planet (or planets) up to twice the size of Earth. All we have to do is look for them and eventually (given more powerful search methods), we’ll find them.

Then, the next step will be to figure out if any of those worlds have conditions suitable for life. That’s a painstaking project because it requires measurements of planetary atmospheres. You can’t look directly at a planet, they’re overpowered by the light of their stars. But, the light of their stars CAN be studied as it passes through those atmospheres. If life exists in those atmospheres, its “effluent” will show up in the chemical analysis of the atmospheres.

The next step after THAT is to determine what kind of life is on a given planet.  Beyond that, we’d simply have to send a signal to the planet with the evidence for life and hope for the best.  Unlike in science fiction, however, when space ships zoom around at warp speed and can seem to cross gulfs of space during the commercial break (on TV), any message we might send (and we’ve already sent some, plus more than 75 years worth of our TV and radio broadcasts out to space) has to travel at the speed of light. So, if the planet we find is 65 light-years away (for example), then if there’s any life on it, we have to wait for the message to actually GET there, wait some more for them to figure out what we’re saying, and then compose a suitable reply. We’re looking at a minimum of 130 years for a simple, “HI, we’re here!” to get there, get read, and a cheery, “Hi, so are we! Wanna swap math problems?” reply.

I think that most astronomers are motivated by that “search for ET” ideal in their hunt for exoplanets. But, they also have other strong scientific reasons for doing this type of work.  More than 400 of them met at NASA Ames Research Center in California to talk about Kepler’s exoplanet findings. Yes, it’s a very hot topic right how. It’s the kind of science that tells us about distant planets, but also helps us understand the formation and evolution of the solar system. It has made discoveries about variable stars, and seismically active stars. It tells us that processes are the same throughout the galaxy and the universe.

In that light, then, the discoveries the astronomers shared with each other and the world are some of the most important ones ever made. They not only tell us that our place in the universe is like other places in the universe (that is, stars with planets), but that the life we take for granted MIGHT also exist elsewhere, too. To put it more simply, our galaxy is a teeming metropolis of millions of little stellar neighborhoods.  Now we just need to find out what life is like in those places!