Exoplanets and the “Big Picture”
Well hello, fancy people. I am honored and thrilled to be here sharing my love of the universe. My name is Nicole, and some may know me as NoisyAstronomer or just “Noisy.” There are various reasons why that is which I’d be happy to tell you over a bottle of cabernet. Let’s just get started with the science, shall we?
I’m still recovering and catching up on work after a week and a half of conference goodness where I’ve been networking, learning lots of new science, and presenting some of my soon-to-be finished thesis work in astronomy. One of these conferences was the American Astronomical Society Meeting (affectionately called “the double-‘A’-‘S'”) in Austin, Texas. This is, of course, one big nerd-tastic gathering of some 2700 astronomers who gather to participate in workshops, give talks, hangout in pubs, and make fun of the movie “Armageddon.” (No really, we did that.)
If you follow your space news, then you might have noticed a serious bump in the amount of news stories coming from the meeting’s many press conferences. Wednesday was unofficially “exoplanet day” as astronomers working on various projects unleashed a torrent of exoplanet discoveries upon the world.
Exoplanets have been a hot topic for over a decade now, and by now you might be getting a sense of “burnout” from these news stories. When I was a kid, there were 9 planets that we knew of, all orbiting our home star, the Sun. Today, there are several hundred planets known to orbit other stars in our Galaxy, with hundreds more candidates waiting to be confirmed. Just discovering an exoplanet is not newsworthy, so the race is one to find the smallest, weirdest, and other “-est” worlds out there.
So who wins the smallest prize for now? Three new exoplanets discovered by Kepler were found that are smaller than Earth in radius, the smallest being about the size of Mars. Just a decade ago, the only planets that we could detect were massive gas giants as big as or bigger than Jupiter, the king planet of our own Solar System. Improved techniques and better instruments are now letting us see planets that may be more like our own Earth. In fact, that’s what the Kepler Mission was specifically designed for, to find an Earth-sized planet in an Earth-like orbit around a Sun-like star. That may sound a little, well, biased, but we know at least one instance where life exists on a planet like that. The search for exoplanets is at least partly motivated by the search for life elsewhere in the universe.
This brings me to one of the other interesting exoplanet news items from the AAS. A six-year-long project using the Hubble Space Telescope has determined that our Galaxy alone has 100 billion planets in it. Stop. Think about that. Our little corner of the universe has 100,000,000,000 planets. Whaaaa…??!
Okay, I just said that we’ve detected several hundred, maybe a thousand. How does one get to 100 billion planets? The Universe is a BIG place, and astronomers cannot always count every instance of something cool going on. So, we take samples and extrapolate. This particular team studied 40 “micro-lensing” events, or 40 instances where a background star was temporarily brightened by the gravitational lens of a passing star between it and us. Three of those showed a second brightening event which indicated the presence of a planet. Yes, sometimes we have very small samples from which to detect entire worlds. That’s science on the edge, baby.
Since micro-lensing is such a rare event, seeing three planets this way is actually rather significant. Take into account the whole Galaxy, and you get about one planet per star. Of course, some stars have lots of planets, and others have none. (And some stars go “wee wee wee” and we call them pulsars!) We want to get a good handle on the number of planets in the Galaxy since that factors into the famous “Drake Equation” that, given certain assumptions, lets you estimate how many intelligent civilizations we may be able to contact right now in the Milky Way Galaxy.
Written as an equation, this is actually one astronomer’s way of organizing topics for a conference about extraterrestrial life. That’s right, not a precise equation, but a list of discussion topics. In 1961, Frank Drake hosted a conference of about a dozen scientists to discuss the plausibility of finding intelligent life beyond the Earth at the National Radio Astronomy Observatory in Green Bank, West Virginia. For the record, it also makes an excellent syllabus outline for a college class on this topic.
Fifty-one years later, we still only know the first variable, the rate of star formation in the Galaxy, with certainty, though with this recent measurement with Hubble, we are closing in on the second factor, the fraction of these stars which have planets. Luckily, for ET hunters, that number seems to be pretty high. Unfortunately, however, other factors are completely unknown to us, such as what fraction of these planets are habitable, what fraction support life, and whether that life will actually become sentient and technologically advanced. In fact, we don’t even know how to begin to ask some of those questions. In science, figuring out the right question to ask is half the battle.
Later in life, Frank Drake has come to the conclusion that the number of communicating civilizations in the galaxy is most heavily dependent on the last, most speculative factor, the lifetime of such a civilization. Humans have only been playing with radio signals for a little over a hundred years in our 200,000 year history as a species during a 4.5 billion year history of life on this planet. What happens if we don’t survive our own technological adolescence? Have other beings made it past this point?
It is so hard to ponder such big questions with a finite human brain in such a short human lifetime. But that doesn’t mean that we are going to stop looking and thinking about these hard questions. Who knows, if humanity one day makes contact with another sentient species, or if we travel to Earth-like planets beyond the Sun to extend our civilization, our descendants will look back at this time in history as the time we started it all, with our little telescopes of glass and metal orbiting a tiny world in the outer edge of a spiral arm of just another galaxy in the Universe.