A Plethora of Alien Seas -- Berardelli 2006 (908): 1 -- ScienceNOWOf course, when you increase the value of one term in the Drake equation, given the 'great silence', you decrease another term. The one that keeps shrinking is the lifespan of technological civilizations interested in travel, exploration, and communication. The civilizations must either all die or all lose interest in communication. (The other explanation for the great silence is the one favored by odd couple of religious fundamentalists and simulationists -- it's by Design.)
.... The researchers found that when gas giants migrate, they fling lots of rocky debris away from the star and into the habitable zone, where liquid water can exist on a planet's surface. There, the debris frequently coalesces into Earth-sized planets.
This kind of early evolution also perturbs the disk, causing comets outlying billions of kilometers away to dive toward the star. Enough of these ice balls hit the terrestrial planets to deliver large quantities of water. "We were very surprised to learn that these planets are water-rich and probably covered in global oceans," he says.
The findings suggest that thousands of planetary systems within the Milky Way could harbor Earth-like planets, says Rory Barnes, a planetary scientist at the University of Arizona in Tucson. Still, he cautions that the key question is how many planetary systems have hot Jupiters...
Sunday, September 10, 2006
One of the explanations of the Fermi Paradox is that earth-like planets are very rare, so technologic civilizations are very rare. This was the premise of a 6/17/2000 Scientific American article that inspired my interest in this topic. Since then, however, every discovery in plantetology has increased the prevalence estimate for earth like planets. Now new models of planetary formation suggest gas giants support, rather than oppose, the formation of earth like planets: