Life forms other than life on earth are referred to as extraterrestrial life. Humans have been trying to answer the question of ‘Are we alone ?’ from time immemorial. The answer is not sure; even with our scientific advancement, we still didn’t trace any radio signal or found any living forms of life. The human race is still in search of other life forms. Scientists are still trying to find the evidence. Among all the life forms, human civilization expects a more advanced and intelligent society. Maybe these questions show us that we still need to understand more about life on earth.

Q. How is life on earth formed?

The early attempts to explain life on earth were related to spiritual beliefs and god. The other theories involve the concept of spontaneous origin, which states that life originated from non-living things and became more complex and complex. Later the experiments by Francesco Redi and Louis Pasteur strongly disapproved of this theory. Afterwards, many other ideas stated that life originated outside earth and was brought to land and other concepts. One of the widely accepted theories is the biochemical theory of evolution proposed by A I Oparin and J.B.S Haldane, which suggests that organic molecules, which are building blocks of living organisms, can be formed from the simple inorganic molecules present in primitive earth conditions. In 1953 Stanley L MIller and Harald C Urey experimented with this theory by passing an electrical discharge through a glass flask containing ammonia, hydrogen, water, and methane to stimulate the early earth condition; the experiment resulted in creating organic molecules such as amino acid. In further investigations, exposure to UV rays also resulted in the production of other complex molecules. This experiment also explains the need for an oxygen-less environment and why the process is not happening in the present conditions. 

Q. What are extraterrestrial life and exoplanets?

The planets located beyond our solar system are termed exoplanets. It is estimated there are more exoplanets than stars in the galaxy. The planets can revolve around a star or can are-floating called rogue planets. The first exoplanets were identified in the 1990s, and afterwards, the scientific world discovered thousands. Many techniques are used to determine the exoplanets. The leading five methods include the wobbling of stars or doppler spectrography– the gravitation of planets, even if it is the minimal wobble of the star which differs the wavelength of light we observe, Transit method – simply searching for shadows observing the dimming of light when the planets pass in between the principal and the observer, Direct imaging – using technology to get the direct image by eliminating the glare of the star, Gravitational Microlensing – detecting the bending in between the star on earth, Astrometry – seeing the change of position of the star(wobbling ) in relation with nearby stars position due to the gravitation effect of an exoplanet. Even when the spectrography of light passing through the exoplanets and comparing it with the direct light from the star helps us to determine the constituents of the planets. This helps us in search of extraterrestrial life like us. While searching for extraterrestrial life, we hope to find a world similar to ours. Hence, the scientific world even categorized the habitable zone –  the distance from a star at which liquid water can exist in orbit. Every lead has a habitable zone, but where it lies differs for stars with varying brightness and size. In 2017, scientists discovered a planetary system at about 40 light-years called Trappist I, which has seven earth-sized planets around a single star and all are in the habitable zone.

Q. What type of life are we searching for?

We may encounter life forms of which we are not aware. The scientific world is looking for life forms similar to us and detecting the planets beyond our solar system having the suitable condition to form a carbon-based life form as we find on earth. Even on earth, we have extremophiles which can exist in extreme conditions, and other organisms, such as Tardigrades which redefine our concept of conditions for life. On the other hand, the scientific world is also researching the possibility of other life forms like silicon-based ones. Still, if such life forms exist, they will only exist in high temperatures, so maybe we will not meet them; no result of such life forms is possible in any experiments, or no evidence has been found. Meeting an advanced intelligent life is a hope and nightmare of humankind. We even sent a phonograph disc in Voyager I, which contains the selected sound and images to show the diversity of earth as a  message to extraterrestrial life. In this search, we tried to explain the type of civilization we will encounter. In 1964 Russian astrophysicist Nikolai Kardashev defined three classes of society which can exist based on how they harness energy which is known as the Kardashev scale. He proposed this idea by suggesting signals of what energy scientists need to look for; maybe there has been an ancient civilization which would have harnessed energy which is impossible for humans. Kardashev scale makes humankind think ahead to look at how to extend cultures would have gone. Type I civilization –  The civilization which can harness all the energy of the planets they reside in.

Type II – The civilization which can harness all the energy emitted by its star. If we reach this, we can harvest the power of 4 ^{10^26} W out of our star. This type of civilization will be able to construct the Dyson sphere– a theoretical structure that can extract all the star’s emitted energy. 

Type III-  the civilization capable of harnessing all the energy output of the entire galaxy; if we take the milky way as an example, it comes around an order of 1036 W. Later, other scientists proposed a higher class of civilizations. According to the new classifications of the scientific world, humans are at 0.72 on the Kardashev scale and still did not reach the Type I civilization.

Q. Will we find alien life in the near future?

In 1961, the astrophysicist Frank Drake proposed Drake’s equation which calculates the Number of intelligent civilizations possible in the galaxy. Under many factors, it predicts a large number of cultures out there. 

N = Number of civilizations in the milky way we can detect 

R* = star formation rate 

f_p = The fraction among the star having planets 

n_e = The Number of planetary systems among them having conditions suitable for life 

f_l= The  fraction of planets that develop life on it 

f_i =  The fraction of  planets having intelligent life among the worlds creates life 

F_C = The  fraction of the intelligence life which generates communication and releases detectable  signal 

L = Years a civilization exists or sends an alert to space. 

When Drake tried to answer the probability that extraterrestrial intelligent life mathematically can communicate, a simple question asked by physicist Enrico Fermi contradicts our understanding – ‘Where are they?’ – known as the Fermi paradox, which questioned why no civilization visited earth still now. As mentioned by one of the SETI scientists, Jill Tarter drake’s equation is an “ä wonderful way to organise our ignorance  ”. Still, against all odds, within our limit of knowledge, we are searching for life or habitable environments within our concept of life, searching for signals from outer space and waiting for signs like the mysterious ‘WOW’ signal we received in 1977.