An observable universe may contain 100 billions of galaxies. Galaxies contain dust, gas, dark matters countless stars and Planets. Our solar system consist of the Sun as the average size of star and eight planets, satellites of the planets, numerous comets, asteroids and the interplanetary medium and of course gas and dust particles. Among eight or nine planets (if Pluto is also considered as a planet) only the Earth is known to support the living beings. As it contains suitable environment for living they are water, air, soil. The question raised is the “Are we alone?” What if not only water, air and soil are only the basic component of the life? What if there are other solar systems within the galaxies and what if there are planets like the Earth, what if there is another planet which supports the life. As study of these things are too difficult as study of existence of god or ghost.
There are obviously two kinds of people,one who believe in the existence of the life in another planets or existence of extraterrestrial while the other type who always deny this fact. There still exist some group of people who think the earth is flat though it is oblate Spheroid so, many people easily deny the fact of the existence of extraterrestrial. There are no such evidences yet to openly confirm the existence of extraterrestrial or aliens but there are many researches that have been done regarding its existence. So it is considered as the hypothetical life form that might range from simple living such as bacteria to the advanced life form than humans.
Few interesting probable extraterrestrial incidents are: