Alien life, such as bacteria, has been hypothesized to exist in the Solar System and throughout the universe. This hypothesis relies on the vast size and consistent physical laws of the observable universe. According to this argument, made by scientists such as Carl Sagan and Stephen Hawking, it would be improbable for life not to exist somewhere other than Earth. This argument is embodied in the Copernican principle, which states that the Earth does not occupy a unique position in the Universe, and the mediocrity principle, which suggests that there is nothing special about life on Earth.[7] Life may have emerged independently in many places throughout the Universe. Alternatively life may form less frequently, then spread between habitable planets through panspermia or exogenesis.[8] In any case, complex organic molecules necessary for life may have formed in the protoplanetary disk of dust grains surrounding the Sun before the formation of the Earth based on computer model studies.[9] According to these studies, this same process may also occur around other stars that acquire planets.[9] (Also see Extraterrestrial organic molecules.) Suggested locations at which life might have developed include the planets Venus[10] and Mars, Jupiters moon Europa,[11] and Saturns moons Titan and Enceladus.[12] In May 2011, NASA scientists reported that Enceladus is emerging as the most habitable spot beyond Earth in the Solar System for life as we know it.[13] Since the 1950s, scientists have promoted the idea that habitable zones are the most likely places for life to be found. Numerous discoveries in this zone since 2007 have stimulated estimations of frequencies of Earth-like habitats numbering in the many billions[14][15] though as of 2013, only a small number of planets have been discovered in these zones.[16] Nonetheless, on November 4, 2013, astronomers reported, based on Kepler space mission data, that there could be as many as 40 billion Earth-sized planets orbiting in the habitable zones of Sun-like stars and red dwarfs in the Milky Way,[17][18] 11 billion of which may be orbiting Sun-like stars.[19] The nearest such planet may be 12 light-years away, according to the scientists.[17][18] Astrobiologists have also considered a follow the energy view of potential habitats.[20][21] No widely accepted evidence of extraterrestrial life has been found; however, various controversial claims have been made.[22] Beliefs that some unidentified flying objects are of extraterrestrial origin,[23] along with claims of alien abduction,[24] are dismissed by most scientists. Most UFO sightings are explained either as sightings of Earth-based aircraft or known astronomical objects, or as hoaxes.[25] In November 2011, the White House released an official response to two petitions asking the U.S. government to acknowledge formally that aliens have visited Earth and to disclose any intentional withholding of government interactions with extraterrestrial beings. According to the response, The U.S. government has no evidence that any life exists outside our planet, or that an extraterrestrial presence has contacted or engaged any member of the human race.[26][27] Also, according to the response, there is no credible information to suggest that any evidence is being hidden from the publics eye.[26][27] The response further noted that efforts, like SETI, the Kepler space telescope and the NASA Mars rover, continue looking for signs of life. The response noted odds are pretty high that there may be life on other planets but the odds of us making contact with any of them—especially any intelligent ones—are extremely small, given the distances involved.[26][27]
Posted on: Fri, 18 Jul 2014 14:23:33 +0000
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