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Other planets like Earth
Carl Sagan imagined that perhaps when we look up at the sky at night, near one of those faint pinpoints of light is a world in which someone quite different from us is then glancing idly at a star we call the Sun and entertaining, just for a moment, an outrageous speculation. He said it is very hard to be sure because there are several impediments to the evolution of a technical civilization. Even if civilizations arise repeatedly, inexorably, on innumerable planets of the Milky Way, they could be generally unstable, so all but a tiny fraction are unable to survive their technology and succumb to greed and ignorance, pollution and nuclear war. This is what he conjectured in his book (and TV series) Cosmos, and it looks quite like he was admonishing us about the insidious and subtle challenges that generation after generation of earthlings faces when dealing with these problems of greed, ignorance, pollution and war.
N = N*fpneflfifefL , where N* is the number of stars in the MilkyWay Galaxy; After some considerations about each factor of the equation, he posits some possible numbers for N and sadly concludes that "Civilizations would take billions of years of tortuous evolution to arise, and then snuff themselves out in an instant of unforgivable neglect". You can see several texts about the Drake equation on the Net at: www.seti-inst.edu/science/drake-bg.html www.planetarysystems.org/drake_equation.html Google brings 1,490 sites about the Drake Equation. Charley Lineweaver and Daniel Grether, of University of South Wales in Australia, made some calculations about the existence of Jupiter-like planets in other host stars´ systems, like the sun´s. Lineweaver says that "our solar system is Jupiter and a buch of junk". Jupiter´s importance to us is that its great mass and gravitational field shield the Earth against comets and asteroids, like it happened in 1994 when its immense gravity lured the Shoemaker-Levy comet into a dead plunge. Says Robert Roy Britt, from Space.com: "Had the comet hit the Earth, it would have sterilized much of all the planet". So Lineweaver and Grether worked out some calculations for the prevalence of planets that are about the same distance from their host stars in order to find smaller objects in a more comfortable orbit between "Jupiter" and their host star. Lineweaver believes there´s a billion of Jupiters orbiting Sun-like stars, and he explains: "There are about 300 billion stars in our galaxy. About 10 percent are roughly Sun-like. At least 5 percent but possibly as many as 90 percent or 100 percent of these have Jupiter-like planets". He adds that a reasonable guess is the same number of Earths as Jupiters. Alan Boss, from the Carnegie Institution of Washington,
said that the calculations of Lineweaver are reasonable,
and that "as the veil covering the unseen portions
of discovery space is lowered in the next decade, I expect
we will find that Jupiter-like pllanets are common place.
Wheter or not that also means Earth-like planets are common
can only be proven by NASA´s Kepler mission",
recently approved to launch in 2006 and that will monitor
100,000 stars for telltale dips in light indicating an
Earth-sized planet in Earth-like orbit has crossed in
front of the host star. Kepler will provide the first
census of planets that have the potential to support life.
In his book Carl Sagan told us that N could be more or
less 10 planets, but he added that "if 1 percent
of civilizations can survive technological adolescence,
take the proper fork at this critical historical branch
point and achieve maturity, then ft = 1/100 and N = 107,
and the number of extant civilizations in the galaxy is
in the millions". Let´s wait and see. Related news:
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