Exoplanets

Where are they? That question asked the famous physicist and genius Enrico Fermi during a discussion with his colleagues when having a lunch break from their daily work with developing the nuclear bomb at Los Alamos National Laboratory in 1950.
There are billions of stars in the milky way that are similar to our sun and many of them are billions of years older than our sun.
Some of these stars should with high probability have Earth-like planets and some may have civilizations with more advanced technology than us. Should not this life has been able to spread all over the galaxy at this time? So why can we not see any trace of aliens here? This paradox is called Fermi's paradox. Some popular explanations to the paradox are: 

• When civilizations envolve enough advanced technology the inhabitants could create a kind of virtual reality and no longer care about the actual reality. 
• We won the lottery. The probability of life developing and last so long is so low that it only happened once, on earth.  
• Civilizations destroy them self before they invent interstellar space travel. By war or by environmental pollution or natural disasters.
•  Aliens are too different from humans perhaps they see us as to primitive species and does not contact us to avoid interfering with our natural development   
• The civilization on Earth has not been around long. We started transmitting radio waves in 1906 to short of a timespan to extraterrestrial to notice us. And we have not been looking enough for signals in space to notice them.

Image Credit: The digital artist

Search for extraterrestrial intelligence SETI is a term for scientific searches for intelligent extraterrestrial life. And several SETI program and initiatives have in decades been monitoring space in search for signals from other civilizations on exoplanets.
In the previous article, I wrote about Breakthrough Starshot that is founded by Russian billionaire Yuri Milner. He also found the project called Breakthrough Listen that are using large radio telescopes for listening for signals. One of the founders of SETI is the American astronomer and astrophysicist Frank Drake.

Frank Drake is well known for the equation from 1961 that bears his name. Drake’s Equation is a probabilistic equation that could be used to estimate the number of active communicative extraterrestrial civilizations in our galaxy.

The Drake equation is: N=R* f_p n_e f_l f_i f_c L  
N = number of advanced technological civilizations that could communicate 
R* = The yearly rate of formation of stars suitable for developing life in our galaxy
f_p = The fraction that has exoplanets
n_e = The average number of habitable planets per planet system
f_l =The fraction that will develop life
f_i = The fraction that will develop intelligent life
f_c = The fraction that will develop advanced technological civilizations 
L = The average life length of advanced technological civilization 
We cannot use Drake's equation to make estimates. Because we don’t have enough data/knowledge yet to give any values or really good guesses for these terms.
The rate of star formation is not a constant over time. When the universe was younger stars where being format at a higher rate. Today we could estimate R*  to between 5-20  new stars per year in the Milky Way. We have when this article is written discovered 3875 exoplanets and that 55 could be habitable. 
Even our closest star has exoplanets. Which give a higher estimate for f_p and n _e We don’t know anything about f_l  the only thing we know that is that life has developed on earth. If we find organisms on other celestial bodies in our solar- system like Mars or Jupiter/Saturn's moons it would indicate that life could be common on other solar systems. 

Check out our interactive star map that shows the discovered exoplanets that have an earth-similarity index bigger than 0.7 and could possibly support life.