As of May, the Kepler telescope had discovered 1,284 exoplanets. The total number of discovered exoplanets in the entire history of astronomical observations is more than three thousand. They are all outside the solar system and revolve in orbits around their stars. The main question is - can at least some of them be inhabited?
there is hope
It would seem that with so many stars and exoplanets, it is safe to say that we cannot be alone in the Universe. But there is no officially recorded convincing evidence confirming the existence of aliens.
And what do scientists say on this topic? The May issue of Astrobiology magazine published an article by the professor of astrophysics at the University of Rochester, Adam Frank and his colleague, astronomer Woodruff Sullivan, in which it is noted that although we do not have exact information about the existence of advanced extraterrestrial civilizations in our Galaxy today, we can almost certainly say that they existed at earlier stages of cosmic history.
Drake's Seven Conditions
Let's turn to the well-known Drake equation. In 1961, at the request of the National Academy of Sciences, astronomer Francis Drake tried to derive a formula that determines the theoretical number of civilizations that can come into contact with us.
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It is clear that for the establishment of "interstellar communications" civilizations must have a sufficiently high level of development. The scientist has included in his equation seven factors, on which, in his opinion, depends on the number of our possible space "partners".
First, it is the number of stars born annually. Second, the number of stars with planets. Third, the number of planets per star orbiting in the so-called "habitat" zone. Fourth, the number of planets where life was actually able to originate. Fifth, the proportion of planets where life has been able to develop to reasonable. Sixth, the development of civilizations to such a level that they could come into contact with their own kind in other regions of space. And, finally, seventh, this is the average period that such a "technically advanced" civilization can exist.
I must say that at the time Drake compiled his equation, of all the factors mentioned, only one was known - the number of stars forming annually. Therefore, discussions started - for example, what could be the number of planets where life is capable of forming?
Some researchers have built models according to which it can be quite large. Others have argued that it is close to zero. But after all, before our eyes there was only one example of an inhabited planet - our Earth.
Or take such a parameter as the average lifespan of a civilization. It is assumed that in order to establish contact with another civilization, the inhabitants of the planet must be able to send radio signals. Earthlings have been using radio communications for a little over 100 years. How long will we last? A thousand years? One hundred thousand? Million? Who can answer this question? If most civilizations do not live too long, then it turns out that most of the Galaxy is not inhabited.
Today, three of the seven factors mentioned in Drake's formula are already known. In addition to the number of stars that appear annually, we know that the proportion of stars with planets is almost 100 percent. Moreover, 20-25 percent of the planets are in the habitable zone, where there are conditions for the emergence of life - for example, water in liquid form.
Backward calculations
Frank and Sullivan, meanwhile, decided to "go from the opposite" and find out what is the likelihood that our earthly civilization is the only technically advanced of all that ever existed in the Galaxy. Calculations have shown that even with the smallest probability of the appearance of such civilizations, we are still, most likely, not the first.
Even if the odds were one in ten billion, there would still be a trillion "advanced" civilizations in the entire history of space. Simple math!
So the chances that earthlings are the only ones, much less than that there are other intelligent beings … It's another matter whether they exist simultaneously with us, existed long before us, or will exist many centuries after us …