Hello, is there anyone out there?

When did the search for extraterrestrial life begin? What are they looking for today and by what means? And what are the chances that an alien spaceship will land on our street like in the movies? A brief history of gastrobiology

Article: Bat-Sheva and Gon-Galamidi, a young Galileo
Big head, thin body and long arms? Playful little green creatures or a terrifying slime monster? Close your eyes and try to imagine - what would an alien look like? It is likely that the alien you imagined is very similar to the one that appeared in the last science fiction movie you saw. Although books, movies and television are full of aliens, in reality not even one small alien has been discovered to date. And it's not that we're not looking.

Humans have been searching for extraterrestrial life for hundreds of years. when did it start As soon as we realized that we are not really in the center of the universe. Until less than 500 years ago, everyone was sure that the Earth was in the center; The sun, the moon and the stars revolve around him; And the whole universe was created in honor of the life on earth. With such a perception, who thought of looking for life elsewhere? The great revolution came when Nicolaus Copernicus determined that the Earth was just one of several planets revolving around the Sun. Later we realized that our sun is not really special either, it is just one of hundreds of billions of suns that make up our galaxy - the Milky Way galaxy - and is located somewhere on its outskirts. And if all this already makes us feel a little less special, then for several decades we have known that our galaxy is not special at all - it is just one of the hundreds of billions of galaxies in the universe. But according to everything we know so far, our little planet is the only place where life has evolved. So there is probably something special about him, even very special.
What is "life" anyway? According to the definition agreed upon by biologists, a creature is considered alive if it has the ability to reproduce itself, i.e. if it knows how to reproduce and has genetic continuity, and if it has the ability to experience evolution, i.e. small genetic changes, thus being adapted to changing environmental conditions.

A message to the aliens
The search for extraterrestrial life focuses mainly on the search for intelligent civilizations on the one hand, and on the search for microscopic creatures on the other. Let's face it, intelligent extraterrestrials excite the imagination much more than bacteria, so astronomers began looking for signals in space that would indicate the existence of alien civilizations transmitting to us. Following the development of the radio telescope in the sixties of the twentieth century, the SETI initiative was established to search for intelligent life by listening to radio signals coming from space.

Astronomers wanted to transfer the whole matter of aliens from the field of science fiction to real science, and the scientific way is of course with the help of mathematical formulas. This is how the famous astronomer Frank Drake developed a formula that calculates the number of civilizations trying to establish radio communication with humanity. The problem is that the formula is based on assumptions and includes all kinds of variables that are difficult to measure, such as the chance that a certain planet will have life, the chance that life will develop intelligence, and the chance that the intelligent aliens will develop technology that will transmit signals into space. In the seventies, the Pioneer-10 spacecraft was launched, whose goal was to leave the solar system; She carried a disc with a message to the aliens, which was written in a language that any alien with some intelligence should understand...

Does anyone have water?
After all attempts to find clues to the existence of a developed civilization somewhere around the universe (so far) failed, the approach to searching for life in space changed. A new scientific branch was born: astrobiology; This branch deals with the study of extraterrestrial life. Astrobiologists no longer look through telescopes and hope to find an alien waving hello back to us. They focus on scientific questions that can be investigated: What is life? How did life begin on Earth? What environments can support life? How can we determine if there is life on other planets? What would be the biochemical basis for life on other planets? and more.

An important clue to the possibility of life on a planet is the presence of organic molecules. Many probes that landed on planets and moons in our solar system looked for evidence of the existence of organic compounds. Since the life known to us from Earth is based on water (about seventy percent of our bodies are water) astrobiologists are looking for planets that have water in a liquid state, and to date there is no unequivocal proof of such planets. On Mars, for example, many sources of water have been discovered, but because of its low temperature, the water is in a solid state, that is, in the form of ice. On the other hand, astronomers have found geological evidence that there may have been liquid water on Mars in the past: river channels and lakes that dried up. Even on one of Jupiter's moons - Europa - astrobiologists have high hopes: changes in its magnetic field probably indicate an ocean of liquid water under the thick layer of ice.

Astronomers do not stop at the borders of our solar system, and the search continues throughout the galaxy as well. How to begin? First of all, in finding planets. Life cannot develop on hot stars that radiate light (suns), but only on the planets that surround them. The problem is that it is not always easy to find a tiny planet orbiting a huge and dazzling sun, which is light years away from us. For this purpose, the Kepler space telescope was launched in 2009. The gravitational force exerted by the planet causes its sun to move in a slightly elliptical orbit, and the telescope can precisely measure the changes in the speed of the sun, thus finding a planet that orbits it. To date, approximately 1,800 planets have been discovered in our galaxy, but astronomers estimate that there are at least a hundred billion of them!

Looking for a star similar to ours

But finding a planet is not enough. Here, in our solar system there are eight planets (the planet Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune), and of them - only on Earth did life develop. So what is so special here? First of all, the earth is in the "seating zone" (or: "the green belt") - this is the distance from the sun where it is neither too hot nor too cold. The planet Mercury, for example, is too close to the sun, and during the day it has a temperature of more than 400 degrees! At such a temperature there can be no liquid water because it evaporates immediately, and of course there is no life either, at least not like what we know. Mars, on the other hand, is too far away, so all the water on it froze. Astronomers today know how to calculate the distance of a planet from its sun and know if it is in the "seat zone". The earth also has an atmosphere - a layer of gases that surrounds it, and is necessary for the existence of life. The atmosphere enables a living environment, protects the planet from the deadly radiation coming from the sun and maintains a stable weather. A planet that is too small does not have enough gravity to maintain a layer of gases around it, and they evaporate into space. In contrast, a giant planet like Jupiter and Saturn has no solid ground, and is simply a giant ball of gas.

With the help of an infrared telescope, it is possible to identify the components of a planet's atmosphere from great distances. Astrobiologists look for elements in the atmosphere that suggest the possibility of life, such as water, carbon dioxide, ozone and methane. In fact, they are looking for a planet that orbits a sun that is similar to our sun, at a distance that is in the "seat zone" and a size similar to that of Earth.

starting from home
To date, only one planet has been found that meets all these requirements, and it is 490 light years away from us (called Kepler 186f). The journey to another solar system is not possible, at least for today. But the astrobiologists do not despair: why go so far if you can start searching at home? In order to expand the possibilities to other planets that may have life, today we are looking for "crazy" creatures called extremophiles, that is, extreme enthusiasts. No, we are not talking about skydiving and racing car enthusiasts, but those who live on Earth in completely extreme conditions - bacteria. There are bacteria that live in mineral springs at a temperature of 112 degrees, and in glaciers in Antarctica at twenty degrees below zero; Creatures at the bottom of the ocean or in oil wells live at a tremendous pressure of more than a thousand atmospheres; Single-celled creatures have even been discovered in radioactive waste containers! Even our Dead Sea, called the Sea of ​​Death, actually teems with unicellular life.
So what do you think? Will one day a spaceship land on Earth and friendly green creatures will shake our hand, or maybe we are really special in this whole vast universe? To be sure, there is no field where science fiction and real science meet like the field of extraterrestrial life research - astrobiology.

Did you know?

Astronomers affectionately call the Earth "gold". Remember Goldilocks and the Three Bears? The one that didn't like too cold or too hot, too small or too big? The Earth is not too close to the Sun like Mercury - where the water would evaporate, or too far away like Mars - where the water would freeze.

Did you know?

"If there is indeed intelligent life in the universe, then where is it?" asked the physicist Enrico Fermi in the XNUMXs. Paradox Fermi claims - following a mathematical calculation - that if there was a technological civilization on another planet in the galaxy, it should have arrived on Earth a long time ago.

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