The presence of life on other planets outside our solar system is known as "Extraterrestrial life". In other words, it is also called as "Alien's life". These lives may range from a small organism to a big creature with a civilization far old and advanced than our human civilization. Let's explore more about extraterrestrial life. So the first question that arises in our mind is; what is Terrestrial and Extraterrestrial planets?

Terrestrial planets are those planets which are closest to the sun.These are also grouped as inner planets like Mercury, Venus, Earth, and Mars. Here, Terra is a Latin word for earth. All these planets have same structure like earth and so they are called as Terrestrial Planets. 
Extraterrestrial planets (or Extrasolar planets) are those planets which lie outside our solar system and orbits a star. These are also called "Exoplanet".

In 1961, Dr. Frank Drake wrote an equation called "Drake equation" which is used to estimate the total number of active extraterrestrial civilization present in the milky way galaxy.The Drake equation is based on the probability theory on which this equation calculates the number of such civilizations.The study of science which deals with the search for all extraterrestrial lives found outside the earth is known as  "Exobiology".The search mission for extraterrestrial life has been active since mid of 20th century.The search and study are basically focused on the historic extraterrestrial life and a deep search for an extraterrestrial intelligence (SETI) also.Electromagnetic radiations and other low frequencies signals are monitored using this search technology.

Extraterrestrial intelligence and Extraterrestrial life have also a great impact on science fiction (Sci-fi).It is basically related to the imaginary concept of advance science and its technology.These concepts are usually showcased in Sci-fi magazines, Sci-fi museums, Sci-fi movies etc.According to scientists, life is most likely to be present outside the habitable zones which exist around the stars, but only a few planets are discovered till now in these habitable zones. Also according to study and research of data based on Kepler space observatory, there may be more than (35 billion) earth sized planets which orbit in the habitable zones of stars similar to the sun (a solar-type star) in the milky way.

Biochemical properties of a planet play a very important role in the existence of life of an organism or any life bodies.On earth, water mixes up with other elements such as carbon, hydrogen, oxygen, phosphorous, nitrogen etc to create a biochemical process which is responsible for the existence of life on earth. About 29 chemical elements make life possible on earth.Scientists are also searching for essential chemical elements on other planets, mainly on Mars and on Jupiter's moon (Europa).Many scientists and astronauts have observed and claimed to believe that the existence of UFO's is real and so aliens.They also claimed that the aliens visit our earth very secretly and occasionally.They also have a constant watch on our secret mission of space and also on some areas on earth like AREA 51, NASA's space station etc. NASA has been continuously experimenting with Alien's technology and their lifestyle.Scientists also concluded that there may be more than one earth and thus more than one human civilization. The size of the universe itself is a catchy hint for the scientists to believe that there are other many extraterrestrial life (also called an alien's life) present in the universe with high possibilities.Well according to NASA's Report, they have many proofs and hidden secrets of UFO and UFO sightings on earth and in space too. Also, there are other aliens planets that have been already discovered by NASA but are never disclosed or published.

According to NASA, the aliens may be present on some earth's undiscovered lands, forests or deep inside the ocean in the form an organism or other creature/insect form. Well the recent hacked news (leaked news) of NASA  says that "The NASA is on the verge of announcing the proof of aliens and their life".