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What is an Exoplanet ?

It is in human nature to venture beyond what is just visible. Displeased with the uninhabitable nature of planets in our own Solar system, Scientists have begun the tradition of searching for faroff worlds lying thousands of light years away. Planet hunters, as these specialists are fondly called, have discovered about 307 exoplanets till this date. Exoplanet, shortened from extrasolar planet, is a term used to describe a planet not part of our own stellar system. Since the first exoplanet was discovered in 1992, many teams of researchers have offered their part in the big picture. The most happening field in Astronomy right now could be exoplanet research.

The idea of exoplanet hunting is not very new to Astronomers. Back in 1952, American astronomer Otto Struve broke the silence by signifying the possibility of observing planetary companions of distant stars. His idea, though accepted, could not be established until the end of the century, when technology pushed the limits of space observation. Capable of detecting the slightest variations of light from stars in other galaxies, state of the art space telescopes are now aiding astronomers in planet hunting. A line up of new technologies that assist them in identifying and confirming the existence of exoplanets have been invented by planet hunting specialists, Scientists not only discover these exciting farflung worlds, but also estimate their mass, chemical composition and distance from parent star through a variety of ingenious techniques. Most of the exoplanets found till date are giant planets weighing many times the earth. The planet with the lowest mass found till date is the OGLE2005BLG390Lb, weighing approximately 5.5 times the earth. It orbits a red dwarf in the center of the Milky Way galaxy and is about 21500 light years away from us. The most massive exoplanet known is TW Hydrae b, which is some 9.8 times heavier than Jupiter, the heaviest planet of our Solar System. Exoplanets are generally named according to a scheme in which a small letter indicating the planet is added to the name of the star. Many exoplanets have intriguing properties. Some people can't believe that there are planets out there that orbit not one, but two stars simultaneously! The PSR162026c is a good example. It orbits a stellar binary, which is a duo of a pulsar and a white dwarf.

Recently discovered exoplanets have been quite motivating to astronomers as well as astrobiologists. The question of life on these remote planets is ever enthralling. Scientists estimate that the probability of life on a planet depends not just on availability of water, but many other factors including the distance of the planet from its sun. A certain proximity to the parent star, called the 'habitable zone' of a star, determines the possibility of evolution of life on the planet. Most exoplanets have been found to be either too close to their parent star or too distant to support life. One of the latest discoveries, the exoplanet Gliese 581c was found to be in a habitable zone while also hinting an unconfirmed possibility of liquid water. Gliese 581c is one of the three planets orbiting a red dwarf Gliese 581, about 20 light years away from the sun, considered highly close in astronomical distances. Its sister planet, Gliese 581d is also anticipated to be life supporting while it lies on the outer edge of the habitable zone and weighs about 8 earth masses. While this is only the beginning of exoplanet research, it raises many profound questions about the place of humanity in the universe. Astrobiologists particularly are very much interested in these findings as it gives them an opportunity to view life in a fundamental manner. Until more evidence is gathered on the presence of life in other worlds of the universe, each discovery of an exoplanet will bring with it new hope in the scientific community.

In this unconstrained universe with limitless number of mysterious worlds, there could be many lifehosting planets. Someday, we might have knowledge of all planets in our galaxy and maybe even the means to travel to them. Whether there are intelligent beings out in the corners of the universe is a difficult question to answer today. But, there is a fundamental statement made 25 centuries ago by Greek philosopher Metrodorus of Chios: "To consider the Earth as the only populated world in infinite space is as absurd as to assert that in an entire field of millet only one grain will grow."

Christian Nuesch is the creator of Asynx Planetarium, an easy-to-use, free astronomy program that helps render and create sky maps of the moon, planets, stars and constellations. It features time-traversal to simulate motion through past and future, graphics, animations and a location customization feature. You can download the free Asynx Planetarium Software at http://www.asynx-planetarium.com .