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veloped civilization for every 300 galaxies i e ours would be the only such civilization in the milky way and in the nearest 299 galaxies surrounding it the more critical estimations are by rood and trefil 1981 as some authors have opportunely pointed out cf mcmullin 1980 pp 83 84 the principal limit of this type of equation is the lack of a realistic model that satisfactorily describes the processes whose fractions of probability of occurrence are to be calculated for example to know the fraction of stars that could have planets similar to the earth we must have a precise model for planet formation from star clouds this model should also have parameters describing the various characteristics of the formed planets in order to select how many planets would be suitable unfortunately however we do not possess until today such a model things get even more complicated when we consider that we know very little of the why of the origins of life on a planet and even less with respect to intelligent life therefore we do not have a realistic model to evaluate whether or not this must happen a certain number of times or never at all the logic of a statistical theory for example the kinetic theory of gas is to deduce an average behavior for a larger scale on the basis of one s knowledge of known smaller scale processes for example the principles that regulate the motion of a particle a statistical theory for the formation of planets with a biosphere but above all a statistical theory for the formation of life is not rigorously possible because we do not know the modality of these processes that is a complete and reliable theory to interpret them with a sufficient level of accuracy moreover in nature we have a unique known event namely us terrestrials and we cannot securely distinguish what is necessary for our appearance from what might not be necessary in short we have insufficient information inevitably the scientific disciplines that tackle the theme of life in the universe try to use deduction as far as seems reasonable attempting to link our inferences with what knowledge we have of the cosmos and its environments at the same time i believe that in a theme such as ours the attitude better methodically grounded will always be induction together with the patience to wait and discover 2 scientific projects on the research of life contemporary science confronts the theme of life in the cosmos in various thematic contexts they include the research and the study of organic compounds and of biological structures possibly present in interstellar space or on the surface of heavenly bodies comets asteroids satellites or planets adequately hospitable to them the research for at least some elementary form of life in particular places within our solar system the detection and the study of planetary systems formed around other stars in a manner similar to our solar system the theoretical and experimental reconstruction of the processes that might have given origin to life on earth in order to better understand such mechanisms on a cosmic scale and finally the research for possible radio signals of intelligent origin by means of radio telescopes partially or totally dedicated to the sounding out of the sky in centimetric and decimetric wavelengths all this activity has entered the panorama of scientific research as a new discipline called exobiology astrobiology or also bioastronomy the status of knowledge in this area and the main research programs devoted to seek extraterrestrial life are easily found in many published books and reviews including proceedings of international conferences cf for instance papagiannis 1985 shostak 1995 batalli cosmovici et al 1997 grady 2001 goldsmith and owen 2002 dick and strick 2004 meech et al 2007 since 1982 the international scientific community has granted such research activity official status within its international bodies establishing the commission n 51 of the international astronomical union a good number of websites run by scientific institutions among which there is the official nasa website for astrobiology also supply an ever wider public with updated information from a historical perspective the first official entry within a strictly scientific environment of the theme of extraterrestrial life dates back to the second half of the 19th century namely the observation of the channels on mars by schiaparelli beginning in august 1877 their possible intelligent origin was the object of dispute throughout the world for about thirty years the mysterious images were then recognized to be natural structures thanks to the use of observational instruments with a high power of resolution the red planet on which herschel had indicated two polar caps thought to be formed from frozen water but which today we know to be formed from solid state anhydrous carbon remained almost until today a potential candidate for the presence of some elementary life forms mars became the object for space missions immediately upon the birth of astronautics first with the passing flight of a number of probes mariner 1964 1971 then with soft landings on its surface viking in 1976 and finally with reconnaissance missions starting with self propelled automatic probes pathfinder in 1997 both the viking probe and the pathfinder mission conducted experiments to verify the existence of possible forms of life reporting negative results during the first decade of the third millennium more perfected space missions have been projected and carried out projects for mars exploration include the european mars express launched in 2003 and nasa s rovers spirit and opportunity successfully landed on january 2004 the orbiting probes mars odyssey and mars reconnaissance orbiter and the complex phoenix mission which landed on may 2008 water was almost certainly present on mars in the past and water ice evidences have been announced in summer 2008 by phoenix lander but the results acquired within the first decade of the 21st century tend to exclude the possibility of life forms on planets within our solar system due to the prohibitive chemical and physical conditions present within their atmospheric envelopes or on their surfaces by the end of 20th century scholarly interest has shifted to some of the massive satellites of solar system s bigger planets images obtained in the 1970s and 1980s from the pioneer and voyager probes and later from the missions galileo launched in 1989 released a probe to jupiter in 1995 and cassini huygens launched on 1997 began orbiting saturn in 2004 have attracted researchers attention to some of the satellites of jupiter and saturn particular attention has been paid to the jupiter satellite europa due to the discovery of the presence of water there and to enceladus and titan in orbit around saturn which also exhibit very interesting morphological characteristics thanks to the development of earth s observational technology and above all to the use of orbital instruments such as the space telescope hubble many star systems have been identified in the last few years which show a star encircled by one or more planets so far the planets discovered have masses comparable or greater than that of jupiter the majority of these being too close to the central star and therefore ill suited for life an updated information on extra solar planetary systems is available on the website planet quest edited by the jet propulsion lab and the nasa it must be taken into account that present observations tend to pick out only the more massive planets due to instrumental constraints thanks to a new generation of technology such as that of the next generation space telescope which will be operative in orbit during the second decade of the 21st century we will probably be able to identify planets with a small or intermediate mass and make more accurate measurements to acquire information on the possibility that such bodies host a chemistry suitable for life from a theoretical point of view it appears the formation of planets orbiting around a star is a relatively frequent phenomenon although the physical characteristics that would make them hospitable for life are rather restrictive as we have already seen objects of interest for contemporary bioastronomy are not only planets and satellites but also very small bodies such as asteroids and comets and in general the vast regions of interstellar space with radio frequency observations and infrared spectroscopy it has become possible to discover the presence of over one hundred different types of molecules in interstellar space including water carbon monoxide and dioxide ammonia methanol formaldehyde and various carbon silicon and nitrogen compounds as well as a certain number of amino acids many of these molecules some of which have been found directly on meteoric residues or observed on comets are identical to those that characterize the chemistry for living organisms and therefore raise questions about their possible role in pre biotic processes and about their possible origins from biological processes already in existence presently however no nucleic acids or other biochemical structures of a cellular origin have been observed not even within the vast environment of interstellar space that lead us to think micro organisms are present beyond earth notwithstanding the absence of results that might have demonstrated traces of life past or present in environments other than those of our own planet we must recognize that scientific activity confronts us with a new way of considering life a way that for the first time fixes coordinates on the cosmic dimensions and no longer solely on the terrestrial 3 the search for extraterrestrial intelligence within the context of the relationship between scientific activity and the research of extraterrestrial life the seti program search for extraterrestrial intelligence deserves special mention the idea of dedicating radio telescopes to listen for possible intelligible signals coming from places beyond our solar system derives from the suggestion of cocconi and morrison 1959 at the dawn of radio astronomy this suggestion demonstrated the theoretical possibility of terrestrial instruments receiving from space even at enormous distances electromagnetic flux densities comparable to those that we emit here on earth when transmitting ordinary radio programs the authors advice was to begin listening to frequencies adjacent to the neutral hydrogen emission line at 21 cm 1420 mhz which could easily be chosen as a reference point for other technological civilizations given its intensity and diffusion throughout the cosmos in 1967 an echo of a possible radio contact with extraterrestrial civilizations sounded in public opinion when burnell and hewish discovered the first pulsar until goldreich and julian definitively demonstrated in 1969 that such regular and intermittent signals were produced by neutron stars in rapid rotation some believed it was possible these signals were of an intelligent origin jokingly calling them little green men beginning in 1961 a progressive involvement on the part of researchers and the employment of new instruments gradually brought about the formation of the seti institute which provides a good amount of online documentation today the institute has its own projects and researchers but works in collaboration with nasa as also with other major radio astronomy research institutes on the planet in the context of an interdisciplinary discussion the seti academy committee is also worth mentioning in collaboration with other scientific institutions this committee of the international academy of astronautics iaa dedicates part of its activity to the study of the social and cultural consequences of a possible contact with other civilizations and to preparation of possible protocols for communication some international procedures have already been established in case an event of this type were to be verified they foresee independent confirmations of the discovery international bodies to be informed and priorities to follow beyond any optimistic interpretation of drake s equation there is an important factor that provides motivation to sustain seti research as time goes on the volume of space in which the terrestrial radio signals are journeying increases proportionally to the cube of the distance covered by the speed of light the velocity of radio signals during that same time thus the probability for receiving a possible extraterrestrial response likewise increases as time progresses at this time terrestrially produced radio waves have reached the stars and possible planetary systems associated with them inside a sphere with a radius of approximately 70 80 light years allowing us for the moment to conclude that extraterrestrial civilizations do not exist within a distance of around 30 40 light years from the sun computing the time a possible radio answer needs to travel back or if they do exist they are not capable of responding or perhaps do not have the intention to reply to our signals in this context one may refer also to the fact that the great radio telescope of arecibo puerto rico was deliberately used in 1974 to send toward the globular cluster m13 a radio message of 1679 bits in binary code decodable in a black and white image containing information on earth and human biology the research projects for the 21th century involve interferometric radio telescopes in orbit around the earth or on the concealed face of the moon i e in the shadow of signals coming from the earth in order to increase the power of resolution and the sensitivity for reception of possible intelligent extraterrestrial signals for the more optimistic such as the radio astronomer ron bracewell the many technological civilizations that might populate the universe would already have a communicative network in place a kind of galactic club bracewell 1979 which humans must enter sooner or later but the hypothesis that advanced civilizations may have very diffuse presence has often been contested because there has not yet been contact with any of them neither in the present nor in the historical past if there were a million such civilizations in our galaxy they would be separated by a distance of approximately 100 light years from each other historically known as the fermi paradox for the italian physicist who almost as a joke made this type of calculation for the first time in 1950 during a lunch at los alamos this problem is often posed in a colloquial fashion with the question where are they the proposed responses have varied ranging from the suggestion that such contacts may have already happened in ages when humans were not in a position to appreciate them to the fact that there would be a certain resistance to the establishment of such relationships given the enormous technological or even cultural differences differences that could also account for a sort of ...