Extraterrestrial life

       Thousands of years ago, the idea that the planets were populated by intelligent beings was uncommon. The idea was that the planets themselves were intelligent beings. Mars was the god of war, Venus was the goddess of beauty, Jupiter was the king of the gods. In early Roman times a few writers, for example Lucian of Samasota, conceived that at least the Moon was a place that was populated as the Earth was. His science-fiction story describing travel to the Moon was called the "True History." It was, of course, false. The idea of the planets as an elegant celestial clockwork created by the Deity for the amazement and utility of men emerged in the Renaissance. 
         In the year 1600 Giordano Bruno was burned to death at the stake, in part for uttering and publishing the heresy that there were other worlds and other beings inhabiting them. The pendulum swung far in the other direction in subsequent centuries. Writers such as Bernard de Fontenelle, Emanuel Swedenborg, and even Immanuel Kant and Johannes Kepler could safely imagine that perhaps all the planets were inhabited. Indeed, the idea was expressed that the name of the planet gave some hint to the character of its inhabitants. The denizens of Venus were amorous; those of Mars, warlike or martial; the inhabitants of Mercury, fickle or mercurial; those of Jupiter, jolly or jovial. And so on. The great British astronomer William Herschel even supposed that the Sun was inhabited. But as the extremes of the physical environments in the Solar System became clearer and the exquisite adaptation to the environment of organisms on Earth became more apparent, skeptics arose. Perhaps Mars and Venus were inhabited, but surely not Mercury, not the Moon, not Jupiter. And so on. In the last few decades of the nineteenth century the observations of the planet Mars by Giovanni Schiaparelli and Percival Lowell quickened public excitementabout the possibility of intelligence on our planetary neighbor. 

          Lowell's passion for the idea of intelligent beings on Mars, his articulateness, and the wide publication of his books did much to bring this idea to the public attention, as did sciencefiction writers who followed the Lowellian scenario. But as the evidence for intelligent life on Mars withered, and as the environment of Mars was perceived to be more and more inclement by terrestrial standards, popular enthusiasm for the idea waned. By then, scientific interest in extraterrestrial life had reached a nadir. The very enthusiasm with which Lowell pursued the idea of intelligent beings on Mars and the attention that these ideas received from the man in the street repelled many scientists. In addition, a new astronomical field, astrophysics, the application of physics to the surfaces and interiors of stars, had achieved phenomenal success, and the brightest and most enthusiastic young astronomers went into stellar astronomy rather than planetary studies. The pendulum had swung so far that in the period just after the Second World War, there was – in all of the United States – only one astronomer doing serious physical investigations of the planets, G. P. Kuiper, then of the University of Chicago. Not only had astronomers been turned off extraterrestrial life, they had been turned off planetary studies in general. Since 1950, the situation has slowly reversed again; the pendulum is once more swinging. The development of new measuring instruments (a by-product of World War II), at first ground-based and then, more important, space-borne, has produced a massive infusion of basic new knowledge about the physical environments of the Moon and planets. 
          Young scientists have again been attracted to planetary studies, not only astronomers, but also geologists, chemists, physicists, and biologists. The discipline needs them all. We now know that the building blocks for the origin of life are in the cards of physics and chemistry; whenever standard primitive atmospheres are exposed to common energy sources, the building blocks of life on Earth drop out of the atmosphere in times of days or weeks. Organic compounds have been found in meteorites and in interstellar space. Small quantities have been found even in such an inhospitable environment as the Moon. They are suspected to exist in Jupiter, in the outer planets of the Solar System, as well as on Titan, the largest moon of
Saturn. Both theory and observation now suggest that planets are a common, if not invariable, accompaniment of stars, rather than an exceedingly rare occurrence, as was fashionable to believe in the first decades of this century.

Source :       CARL SAGAN
               The Cosmic Connection
             An Extraterrestrial Perspective


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