"The most important fact about Spaceship Earth: an instruction book didn't come with it." - Buckminster Fuller
On April 8th, 2012, less than a month ago as I write, I read an interview in Slate (via New Scientist) with UC Berkeley's Geoffrey Marcy, who, with colleagues, found 70 of the first 100 exoplanets: planets outside our own solar system. When I lived in Los Angeles I'd diligently read any article on science that the LA Times published, and reveled in the latest on "new worlds," and Dr. Geoffrey Marcy's name just kept showing up. He's now into SETI, which I'll get to later...
Let me go back a bit.
In 1998, it was thought exoplanets probably exist in our galaxy, the Milky Way, but if they did, they were probably big hydrogen-helium things like Jupiter, and not Earth-like rocky planets that could possibly sustain life. This was a long, long time ago. Like...14 years ago. Oh, how Things Change!
By New Year's Day of 2012, we knew that, if there's one thing our universe seems really, really good at, it's making planets. It's efficient. Our first exoplanet data arrived around 1998. It seemed we'd located another planet outside our own solar system, and it was a "Hot Jupiter" or "hot gas giant." Pretty cool.
Our statistical techniques became refined, our telescopes better, our detection techniques improved, and we surmised that only a small percentage of stars in the galaxy harbored Jupiter-like planets. We kept improving our instruments and techniques (NASA's Kepler probe has been a real boon, but there are many others that deserve kudos), and realized there were planets with longer orbital periods (the time an object - in this case a planet - takes to circle its star) and there were less massive planets found. The first domino had been pushed over:
Note that this data is from the 19th of January, and there were already nine new exoplanets
found for year 2012; the fat dot on the line 10^0 represents two Earth-mass planets. Also
NB the tiniest exoplanet yet found had already made it into this calendar year!
By 2010, gravitational microlensing/Doppler wobble had improved. Tons of Earth-sized planets in poetential "Goldilocks" zones - just at the right distance from its own star(s), not too hot; not too cold - had been found. We now have good reason to believe that Neptune-like icy planets with large orbital periods are more common than Jupiter gas giant planets. In fact, in 2011, if we took all the exoplanets we knew of within 0.5 AU (astronomical unit: 1.0 AU is the distance from our sun to Earth), around 17% of them were Neptune-like things. One in every six stars had a Neptune-ish planet orbiting only around 50,000,000 miles from it. 6% of all stars were thought to have Earth-like dealios orbiting them within a half of an astronomical unit.
Most astronomers would agree there are about 200 billion normal-sized stars in our galaxy, which meant there were probably millions of Earth-like rocky planets orbiting their stars in habitable zones. Whether they have water - much less methane, which would hint strongly of life there - we just couldn't tell.
Still in 2011, Arnaud Cassan and colleagues, analyzing microlensing data, looked at exoplanets from 0.5 to 10 AU from their own stars. (Jupiter is at 5.2 AU; Saturn 9.5; Uranus 19.1; Neptune about 30, and now un-planet Pluto was at 40. Eris is at 97.) Here's what his team found:
17% of the stars had Jupiter-like mass-planets
52% harbored cool Neptune-y things
62% (!) had Super-Earths orbiting them. (A Super-Earth is 5-10 times the mass of Earth, but nowheres near as big as Jupiter, and smaller but somewhat approaching the mass of Neptune.)
In addition, the most conservative estimate was that for every star in the Milky Way, there are 1.6 planets orbiting from 0.5 to 10 AU
In addition to that, here's something to really make you feel less alone: If there were one and a half planets for every star - in our boondock galaxy - there might be two rogue planets for every star.
What's a rogue planet? It's a planet that has somehow (been ejected via gravitational interactions with its planetary siblings?) become unmoored from its previous orbit around its star; it's a wandering free agent, a nomad, just cruising around the galaxy. These dudes are on parole, just itching to get into some hot action. It was thought - this is way back in 2011 - that these rogue planets were Jupiter-like things. If there are more than 3 planets for every star in the galaxy, and there's 200 billion stars, that gives us - theoretically - at least 600 billion planets in our galaxy...our galaxy being just one of billions of galaxies, admittedly. And then we're now highly suspecting our entire universe is just one of literally countless other universes. So we're really talking about our own backyard here, relatively speaking.
"To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet, only one grain will grow." - Metrodorus of Chios, 4th century BCE. As to "populated," I think the best logic to use is neither true nor false but indeterminate. And who here is not pining for a day when indeterminate collapses into "true"? Aye, but will they have Ray-Guns? Geoffrey Marcy thinks they will have lasers!
Lots has happened on the exoplanet scene since way back in 2011, and I'll get to it tomorrow, as right now I need a little something that will bring me "back to Earth," so to speak, yet allow me to feel like gravity has a tad less hold on me. If you'll excuse me...
Here's an 8 minute clip of Dr. Geoff Marcy from about 15 months ago: