For millennia people have been searching the answer to the principal question if they are the only ones blessed in the entire Universe. It is now totally and absolutely clear that we are the only ones in our Solar system which was unequivocally proved by scientific researches and experiments based on the use of spacecrafts and astronomic observations. However the Sun and its planetary system is just a tiny part of the entire Universe. Therefore there is still a lot of hope and dreams for an intelligent life somewhere else.
The first man who declared that we might not be alone in the Universe and there were other worlds inhabited by living creatures was the forgotten Italian philosopher and the spiritual alchemist Giordano Bruno (1548-1600) who was martyred by the Roman inquisition of the Catholic Church for his heresy by declaring the existence of an infinite, heliocentric Universe. According to him, beyond the visible world there is an infinity of other worlds, each of which is inhabited. This is quite a modern view, isn't it, even though this statement was made during the dark age of the medieval times in the 16th century in his known works "Clavis Magna", or "Great Key" , "Il candelaio", or "The Torchbearer", "Il spaccio della bestia trionfante", "The Expulsion of the Triumphant Beast", "Cena delle ceneri", or "Ash-Wednesday Supper", "Della causa, principio ed uno"; "Dell' infinito universo e dei mondi"; "De Compendiosâ Architecturâ"; "De Triplici Minimo"; "De Monade, Numero et Figurâ."
Today this idea is very popular and many astronomers are in quest for extra solar planets or exoplanets. They are absolutely sure that we are not alone because each of 200 billion stars in our galaxy which is a part of the entire Universe consisting of 100 billion galaxies might have its own planetary system. Therefore the possibility of another life is totally possible based on an irrefutable fact of solar system existence and the laws of probability. The problem, however, is to locate these planets with a help of modern Earth-based instruments and space-placed equipment.
The idea of planetary worlds orbiting stars other than Sun is not new at all. From mere speculation and suppositions to the astronomical amassing of data ( see the works and articles of E. E. Barnard, Carl Sagan, I. S. Shklovskii, John Gribbin, Walter Sullivan, Diana Valencia of the Harvard University, Sara Seager of MIT and others), our predictions and searches for these extra solar rocky or gas planets have spanned well over 2,300 years. Here it is significant to analyze a couple of premises: a philosophical one concerning the existence of additional solar systems based on a probability factor and a practical one in connection with astronomical observations of exoplanets in other systems. Both of them are focused on an existence of an intelligent life somewhere else, thus a nature and an origin of the Universe. If indeed the probability of a meaningfully intelligent life is a strong possibility, then the existence of extra solar planets is a definite. However it appears that there has been no direct observation of a planet outside the solar system; i.e., a viewing of a planetary body via a telescope and/or a photograph.
The beginning of this saga in search of earthlike planets was associated with the name E. E. Barnard who detected in 1916 a small celestial body with a visible proper angular motion in a direction perpendicular to the line of sight. It actually meant that it could not be a distant star as it is practically impossible to observe its motion due to a huge distance between it and the Earth, except in case of a rotation of the latter around its axis. Thus, it turned out to be a red dwarf located in our vicinity - some 4 light years - which could be potentially examined for an existence of some exoplanets revolving around it. The astronomers were enthusiastic about it and Peter van de Kamp detected wobbles in the movement of the Barnard's Star suggesting and proving later a presence over there of two planets with 0.4 and 0.1 Jupiter masses making a rotation around the star every 22 and 11.5 years, respectfully.
It is worth to note that to reveal new planets moving around stars two techniques are generally used: astrometry and perturbation where the aim of the first is to measure proper motion of stars as a function of time and the second describes any abnormalities in their motion. They are widely employed nowadays together with some other methods like direct imaging (a light reflection), astrometric detection, radial velocity (an analysis of blue shift and red shift spectrums), ground-based photometry (shifts in brightness of a star ), occultation, Doppler shift methods (change of wavelength), additional radial velocity measurements, microlensing, and optical imaging., etc. and bring some positive results in discovering approximately 300 exoplanets rotating other stars on usually elongated or circular orbits. If a body is orbiting a star then it affects the circular motion of the star. As one measures the stars linear motion, it will be found that this motion is not in a straight line, but rather in a wobbly, slightly distorted vector due to the presence of a planet or planets rotating around the star. These techniques help us to determine a size, a mass, a velocity of extra solar planets, a shape of their orbits (elliptical or circular) and a time of a single rotation around the star as well as their composition (gas or solid rock material), a presence of water and an atmosphere and its chemical composition.
