Exoplanets in the TRAPPIST-1 system, some of which may potantially host alien life. Credit: NASA/Spitzer Space Telescope

Our Galaxy Is Home To Over 200 Billion Planets Like Earth, But Are Any Of Them Inhabited?

Astronomers estimate that there are more than 200 Billion Earth-like planets. With such a high number of worlds similar to Earth, what are the odds of some of them having developed life on their surface?

Those of us who follow scientific news and discoveries about alien life experience the same rollercoaster of emotions every year. Experts come up with countless new theories, predictions, and reasons for whether extraterrestrial life exists or not. And in the end – 99% speculations, 1% results. Or less.

Every year, the list of celestial targets that could potentially inhibit alien life increases. Discoveries and useful scientific data are piling up, we know the most suitable targets for research, but our technology is not progressing at the rate alien-hunting requires.

The James Webb Telescope has successfully launched, and it should provide an entirely new window of exploring the universe.

We can safely say that no other instrument in history has been as anticipated considering that its main scientific goal will be the search for alien life in any form.

Are any of the planets in the Milky Way inhabited?

The Milky Way alone has somewhere between 200 and 400 billion planets. What are the chances that Earth is the single unique planet with life even in our own galaxy alone?

I am no mathematician and I cannot give credible estimates, but how long do you think would take us to study most, not all, potentially habitable planets in the Milky Way?

What I believe is that even with the most precise scientific data, the most advanced telescopes to date, and all our knowledge about the formation of life, we would have to be extremely lucky to spot signs of alien life.

Said in different words, I believe that extraterrestrial life forms will find us much sooner than we find them. And for now, although I am extremely excited about James Webb and its capabilities, I do not think we will find alien life any soon. At the same time, I believe that it exists even in the Milky Way.

In fact, I believe that life could exist in any galaxy you could think of. For why wouldn’t it?

Drake equation and alien-hunting

The chronology of alien hunting is long and extensive and we really do not have to go back in time when nothing has been achieved today. I will only briefly discuss several theories from last year.

For example, scientists suggested that there could be exactly 36 alien civilizations in the Milky Way in 2020. They reached this number using the famous Drake equation, a formula that could hypothetically be used to guess the number of civilizations in the Milky Way.

Here is some insight into this formula.

Drake Equation

• N – the number of intelligent civilizations that are ready to make contact

• R is the number of stars appearing during the year in the Milky Way galaxy

• Fp is the percentage of stars that have planets in their orbits

• Ne – the average number of planets and their satellites, whose conditions are suitable for the origin of life

• Fl is the probability that life will appear on a suitable planet

• Fi is the probability of the appearance of intelligent life forms on the planets where life is usually possible

• Fc – the ratio of the number of planets on which intelligent life forms are able to connect and seek it to the number of planets on which intelligent life forms usually exist

• L – the time during which intelligent life exists, can make contact, and wants to

The problem with this equation is that there literally are too many problems with it. We have the variables needed for calculations but we do not know their measurements.

Given Drake’s equation, it becomes obvious that the value of N cannot be precisely determined. In addition, if I move from left to right, the estimates of all quantities become more and more abstract. However, this equation should not be estimated only by numbers. Some researchers are convinced that this formula is just a way to organize human ignorance.

Exoplanet Kepler-22b, a potentially rocky world filled with oceans, as seen by the artist. Credit: NASA/Ames/JPL-Caltech
Exoplanet Kepler-22b, a potentially rocky world filled with oceans, as seen by the artist. Credit: NASA/Ames/JPL-Caltech

And if we consider the hypothesis of the existence of extraterrestrial intelligence from a purely mathematical point of view, then the possibility of obtaining an answer to the question of the number of extraterrestrial civilizations is significantly limited.

The value of L is the most important in the whole equation. One cannot know how long a technologically advanced civilization is capable of surviving. And even if we assume that there is only one alien civilization and there are billions of years or even an eternity, then that will be enough to equalize N and L.

Another weakness of the formula is the number of planets on which intelligent life forms can develop. It is estimated that their number should be within 10 thousand in our galaxy. But there is currently no evidence that there is any basic principle that could guide the primary substance in the path of development in Homo Sapiens. And this question will remain unanswered until confirmation is found of the life of at least one planet in the solar system.

Among other things, Drake’s equation does not take into account such indicators as the age of the galaxy itself and the chemical-mechanical parameters, for example, the presence of certain elements necessary for the formation of planets and the origin of life. According to some experts, Drake’s equation does not presuppose a universe that is constantly in dynamics, but a special cosmological constancy.

But despite the “flaws,” Drake’s equation had a strong effect on the way people think. It mainly served as a starting point for the emergence of astrobiological science. Prominent American astrophysicist Carl Sagan praised that the equation shows a high chance of discovering intelligent extraterrestrial life.

And not so long ago, in 2010, the Italian astronomer Claudio Maccone published his version of Drake’s equation – Drake’s statistical equation, which is more complex but also more reliable.

TOI 1338 b, the first discovered planet to orbit two stars. Credit: NASA/Ames/JPL-Caltech
TOI 1338 b, the first discovered planet to orbit two stars. Credit: NASA/Ames/JPL-Caltech

Using the new formula, McCown was able to determine that 4,590 extraterrestrial civilizations could only exist within the Milky Way, which is more than 1,000 more than the number obtained in the classical version of the equation. In addition, the new formula showed that in addition to human civilization, there may be up to 15,785 others with high technology.

But even if the different alien civilizations were equidistant from each other, the average magnitude would be 28,845 light-years, making it impossible for any contact between these communities, even with the help of electromagnetic radiation moving at the speed of the world.

Even if there were so many civilizations, interstellar communication between them would experience very serious technological problems.

Alien life already went extinct?

Later in 2020, another team of scientists came up with a completely different suggestion. They believe that if alien civilizations existed in the Milky Way in the past, they went extinct due to their own technological advancement. If this is true, will humans have the same future?

All in all, the search for alien life is not an easy feat. If it was, we would already be living in a Star Wars/Star Trek-like universe, right?

SETI (Search for extraterrestrial intelligence) has been on the forefront since Drake began his modern tests in the late 1950s. Nowadays, it is a global effort with thousands of scientists, amateur or not, from all corners of the planet.

Then in 2015, Stephen Hawking and a number of his associates announced the most comprehensive search project to date – Breakthrough Listen. With over 100 million dollars in funding, it is a project that should continue for at least 10 years and will scan over one million stars and 100 galaxies. Results get published twice a year and the participating scientists have already made certain achievements.

In the past, we wrote an article about their Exotica Catalog that includes the most likely objects in the Universe for the existence of alien life. You can read the old article here.

What’s important is that people finance such multimillion projects that truly have a good chance of finding something important about alien life. Sooner or later, we will find signs. Maybe alien life exists within the Milky Way, maybe it exists in other galaxies. Science will find an answer but the question is when?

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Breakthrough Listen. (n.d.). Breakthrough initiatives.
Bryson, S., Kunimoto, M., Kopparapu, R., Coughlin, J., Borucki, W., Koch, D., . . . Zamudio, K. (2020, November 03). The occurrence of Rocky habitable Zone planets Around Solar-Like stars from Kepler data.
Kipping, D. (2020, June 02). An objective Bayesian analysis of Life’s early start and our late arrival.
Tsumura, K. (2020, July 30). Estimating survival probability using the terrestrial extinction history for the search for extraterrestrial life.
Westby, T., & Conselice, C. J. (n.d.). The Astrobiological Copernican Weak and Strong Limits for Intelligent Life.

Written by Vladislav Tchakarov

Hello, my name is Vladislav and I am glad to have you here on Curiosmos. As a history student, I have a strong passion for history and science, and the opportunity to research and write in this field on a daily basis is a dream come true.

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