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.

However it should be bored in mind that many of the planetary bodies detected by astronomers have not been confirmed or established as fact in the astronomical community at large. Therefore at present no specific names have been given too many exoplanets. However, some of the newly discovered bodies are called after the name of the star, and are set apart from the star name by an additional letter. For example, one of the stars in question is Peg 51 and the planetary companion discovered around it has been labeled Peg 51 B. It appears that the majority of detected planets are of Jupiter mass or larger, most have circular orbits, most have been detected by radial velocity measurements using Doppler shifts, the majority of them are less than 1 astronomical unit from their star, and except for the pulsars, the majority of the planets discovered are orbiting stars that are similar to our Sun.

Among the major stars with planetary bodies around them which were subjected to extensive observations during the last 15 years it is worth to list the following:

1. Beta Pictoris – which is 58.68 light years from the Earth and might have two planets;
2. CM-Draconis is a subject to extensive photometric observations;
3. 16 CYGNI B might have one planet;
4. Epsilon Eridani (HD22049) – which is 10.7 light years from the Solar system and might have two exoplanets around it;
5. Gamma Cephei is 51 light years away from us and there is a possibility of one planet orbiting it;
6. HD3346 (HR152) could possess one planet;
7. HD 114762 is some 90 light years from our planet and might have several planetary bodies around it;
8. Lalande 21185 is 8.25 years from the Solar system and could have one planetary companion;
9. Peg51 – which is 45 light years from the Earth and has a giant terrestrial planet Peg51B (half of the size of Jupiter) rotating very (unusually) close to it and characterized by extremely high temperature. There might be also an Earthlike planet;
10. Rho 1 Canceri, Rho Coronae Borealis, Tau Bootis, T-Tauri Stars, 47 Ursae Majoris, Upsilon Andromedae and 70 Virginis stars pretty much similar to our Sun might also have single exoplanets or planetary systems (planets and planetesimals) with important physical characteristics (interstellar dust clouds) which make them quite habitable because they have suitable conditions for a liquid water existence and follow a dynamically stable orbit far enough from their respective stars.

With a development of radio telescopes and a radio astronomy scientists also managed to locate exoplanets orbiting pulsars the total number of which today in our galaxy is about 670 units. These types of stars are in fact neutron stars emitting radio waves in a form of pulses. Many of them are part of a binary star system in which the second element might be a star or a planetary object. In general there are two basic theories regarding the formation of planets around pulsars: one, which is known as the Salamander Scenario, is that the planet existed around the star before it went supernova and somehow survived a gigantic energy release, while the other theory known as the Memnonides Scenario is that the planet formed after the star went supernova and became a pulsar. The Memnonides Scenario would also imply that some type of a dust disk formed prior to planet formation. It appears more plausible from the accepted premise of stars and planet formation. Among such neutron stars which can qualify for this phenomenon based on the sound scientific footing are

1. PSR0329+54 with one exoplanet;
2. PSR1257+12 which bares a similarity to our Solar system with multiple planets revolving around it;
3. PSR1620-26 with one tertiary companion in the system similar to the mass of Jupiter;
4. PSR1829-10 with one planet.

At the present moment a few significant programs and projects are under way in this field of astronomical activities which aims are to find new exoplanets, to develop new ways and instruments of observation and detection and to expand our knowledge in this particular sphere.

One issue of paramount importance in determining the existence of extra solar planets, both from a financial and time-saving aspect, is what stars should be examined in this regard? The option is to concentrate an effective photometric search on the old open star clusters monitored regularly and stars that are closely packed together in order to determine an occultation of the stars in question by orbiting planets. Another possibility which takes into account planet detection as well as possible life forms on the planet is to scrutinize K-type and G-type stars for extra solar planets that may lie within habitable zones capable of maintaining both liquid water on their surfaces and relative temperature ranges based on positive greenhouse atmospheric effects. Thus, K stars have temperatures around 4,000 K, while G star – some 5,600 K. In any event the types of aforementioned stars should show great promise for a location of several new exoplanets.

The list of current activities includes ground- and space-based operations:

A/ interferometer studies using an array of optical telescopes on the Earth arranged in a particular sequence to effectively increase a length of this sort of instrument;

B/ high precision studies using telescopes with a large aperture;

C/ use of the Hubble Space Telescope and its Planetary Camera to detect faint companions of stars, such as brown dwarfs because it does not have the capacity to detect planetary bodies. It is a large, space-based observatory which has revolutionized astronomy by providing unprecedented deep and clear views of the Universe, ranging from our own Solar system to extremely remote fledgling galaxies forming not long after the Big Bang 13.7 billion years ago.

This is a unique and diversified instrument orbiting above the distorting effects of the Earth’s atmosphere and has a tremendous scientific and technological value. This is a modern marvel and a truly break-through in astronomy;

D/ The Photometry Precision Method Program (PPM) are a substitute for the failed FRESIP Program (Frequency of Earth-Sized Inner Planets). Its general aim is to look for Earth-sized planets by measuring small intensity changes in a star when it is occulted by an inner exoplanet. It is carried out by NASA;

E/ The Darwin Project is responsible to accumulate evidence that would indicate primitive life on extra solar planets. This is done with a help of an infrared observatory of the European Space Agency. One of its main objectives would be to detect photosynthetic activity by detecting an abundant amount of oxygen or ozone in the atmosphere. Its major premise is that much of religion and philosophy has focused on attempts to perceive how human beings and our world came to existence and that there is a prevalence of planetary systems throughout the universe and the likelihood that other planets have given birth to first primitive and then even advanced and intelligent forms of lives;

F/ High Resolution Microwave Survey (HRMS)initiated by NASA. Its task is to detect signals from approximately 1,000 selected solar-type stars that would indicate technical civilizations, i.e. life on other alien planets

G/ The COROT mission designed by The French Space Agency together with other European countries and Brazil has successfully been in space for over 630 days and is designed to monitor the light curves of selected stars in order to study extra solar planets with a help of a 30-cm telescope. The COROT experiment aims to be a pioneer mission in the discovery of telluric extra solar planets, bodies with properties comparable to those of the rocky planets of the solar system;

H/ GAIA (Global Astrometric Interferometer for Astrophysics) of NASA surveys hundreds of thousands of stars in order to determine the existence of big and lower mass exoplanets. This is an ambitious mission to chart a three-dimensional map of the Milky Way in the process revealing the composition, formation and evolution of the Galaxy. It will provide unprecedented positional and radial velocity measurements with the accuracies needed to produce a stereoscopic and kinematic census of about one billion stars in our Galaxy and throughout the Local Group. This amounts to about 1 per cent of the Galactic stellar population. Combined with astrophysical information for each star, provided by on-board multi-color photometry, these data will have the precision necessary to quantify the early formation, and subsequent dynamical, chemical and star formation evolution of our Galaxy. Additional scientific products include detection and orbital classification of tens of thousands of extra-solar planetary systems, a comprehensive survey of objects ranging from huge numbers of minor bodies in our Solar System, through galaxies in the nearby Universe, to some 500 000 distant quasars. It will also provide a number of stringent new tests of general relativity and cosmology;

I/ The Kepler Mission elaborated by NASA strives to discover and characterize hundreds of alien planets similar to the Earth. IT employs a space borne one-meter aperture photometer with a 12 degree field of view. In addition, it is expected that 80,000 dwarf stars brighter than 14th magnitude will be monitored for flux. During its 3.5-year prime mission, Kepler will continuously monitor a ~100 square degree field-of-view (FOV) in the Cygnus region, with the objective of photometrically detecting transits of Earth-size planets in the habitable zone. The instrument’s high-precision photometry capability, with two available cadence modes (1 minute and 30-minute) is also sufficient for asteroseismology research and other variability analyses of both Galactic and extragalactic sources.

Thus, the abovementioned array of earthy activities outside the Solar system is quite impressive and promising. However to stimulate it further from the philosophical, scientific and practical point of view NASA and other establishments set up special fellowships for scientists who look forward to detecting exoplanets in the Universe. Totally there are three fellowships today such as

The Karl Sagan Fellowship, The Einstein Postdoctoral Fellowship in Physics of the Cosmos and the Hubble Postdoctoral Fellowship in Cosmic Origins. All three fellowships represent a new theme-based approach, in which fellows will focus on compelling scientific questions, such as “are there Earth-like planets orbiting other stars?” The quest for new worlds intensify and our hopes and expectations are growing.