Our solar system: more exception than rule
Instead of scanning the entire sky for messages from an extraterrestrial civilization, another approach could be to identify an extrasolar planet likely to harbor life and focus on signals it emits. Present ability to detect extrasolar planets does not allow detection of planets as small as planet Earth, though, according to Geoffrey Marcy of San Francisco State University and the University of California at Berkeley, the upcoming Space Interferometry Mission will enable us to detect stellar wobbles from planets that small. Meanwhile, Marcy's presentation on "The Nature of Extrasolar Planets" at the American Physical Society's centennial meeting in Atlanta on 22 March 1999 indicated, from observations thus made of larger extrasolar planets, that our own solar system may be more the exception than the rule. Of the extrasolar planets so far identified, all of them with average distance from their star greater than 0.2 AU are in highly elliptical orbits (an AU, or astronomical unit, is the mean distance from the Earth to the Sun). In contrast to the nearly circular orbits of the eight innermost planets of our solar system, these elliptical orbits are believed to result from mutual perturbation of nearby massive planets or from perturbation by passing stars. In any case, these elliptic orbits reflect a far more chaotic existence than in our solar system. Moreover, Jupiter-sized planets in eccentric orbits close to their stars would endanger Earth-sized planets, thus reducing the likelihood than extraterrestrial intelligent life could evolve. However, Marcy noted, only 5% of the stars surveyed thus far have been found to have such Jupiter-sized planets.
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