Carl Sagan sheds light on the efforts to find other intelligent life forms. The effort is great, the chances of success are low, but the payoff may exceed any imagination.
From the site - Science according to the Internet
In the photo above: Jodie Foster in the film "Contact", based on Sagan's book, which tells the story of a scientist who believes she received life signals from space
In recent decades, the human race has begun a serious and systematic search for evidence of extraterrestrial life. Although no one has yet found extraterrestrial living organisms, those involved in the subject have reasons to be encouraged. Robots sent into space have identified worlds where life may have thrived in the past, though it may not today. The Galileo space telescope found clear signs of life on Earth. A sign of his ability to detect life elsewhere, if he encounters it. And in addition, strong and growing evidence points to the existence of an abundance of solar systems
Like ours in the universe.
The scientists involved in finding other life forms approach the matter from its chemical side: humans, like other earthly organisms, are composed of water and organic molecules (an organic molecule contains carbon, but is not carbon monoxide or carbon dioxide).
A modest search strategy would search for organic molecules and water molecules, assuming that where they are found, life is likely to be found. Of course, this way we will miss other possible forms of life, which are not based on these elements, but which can also be reached by other means. After all, if silicon giraffes were walking around on Mars, NASA's imaging spacecraft would reveal them to us.
In truth, focusing on organic molecules and water is not as narrow-minded and chauvinistic as it sounds. There is no comparison to carbon in the chemical elements, both in complexity and in the variety of compounds formed from it. Water is a stable and high-quality vehicle for the dissolution and interaction of carbon molecules. Organic molecules are surprisingly common in the universe. Astronomers have found evidence of their existence in various places, in stardust, meteorites and also in planets outside the solar system.
On cold planets, where water is frozen and unfit to serve as a building material for life, other solutions - liquid ammonia, for example - may be the key to a different type of biochemistry. At low temperatures, chemical assembly of certain types of molecules requires very little energy. Our laboratories, whose temperature cannot equal that of Neptune and its moons, cannot provide us with much information about the chemical activity at such low temperatures. So we still can't say much about the possibility of ammonia-complex life.
Meanwhile, as far as we know, we have to assume that any kind of life will be based on the substances that make up our own life, water and organic molecules. The important organic life molecules are DNA and HRNA, the nucleic acids, which contain the hereditary code, and the proteins, which serve as a catalyst for the chemical processes.
There is a wonderful unity between all forms of life on earth. Their DNA and RNA are arranged in a similar protein structure. The assumption is that the reason for this is the existence of one molecule - a common ancestor for all of them. Will life forms that do not have a common ancestor develop in a different way, or does life require a unique and specific genetic structure? We won't know until we meet extraterrestrial life forms.
The natural place to look for life is our solar system. Robotic spacecraft have explored over 70 planets, satellites, comets and asteroids at distances between 100 and 100,000 kilometers from Earth. The spacecraft were equipped with measuring devices for magnetic fields, charged particle detectors and photometric and spectrometric systems (measuring the emission of light particles). Photographs were also received from Venus, the Moon and Mars. The findings did not yield anything that proves, or even hints at, the existence of extraterrestrial life.
The Galileo research spacecraft actually discovered life in the solar system. She showed that the existence of such is most likely in one of the planets: Planet Earth. The spacecraft indicated high brightness in the image received from Earth, a sign of oxygen molecules absorbing the radiation. Galileo also noticed the existence of methane, the marsh gas, on the surface of the earth. The quantity is extremely faint, a density of one in a million, but it is still unique. In a system where there is so much oxygen, the methane is expected to combine with it and disappear. The existence of methane nevertheless is evidence of its secretion by living organisms, marsh bacteria and ants.
And perhaps most importantly, Galileo recorded radio broadcasts from the country. There are such broadcasts to indicate the existence of a technological civilization on the planet from which they come. Well, Galileo discovered the existence of life on our planet. Galileo did not innovate much for us with this discovery, but it has something to show that if there was life similar to earthly life in another celestial body surveyed by her, we would have known about it.
Mars, relatively very close to us, has an atmosphere, poles, seasonal temperature changes and a 24-hour day. Generations of scientists, writers and dreamers believed that life might exist on it, but the findings in our hands do not indicate even a hint of it. Living organisms were discovered on the surface of meteorites from Mars, but it is very likely that these were attached to them, after they landed in Israel.
Was there life on Mars in the distant past? Everything depends on the answer to the question: how quickly life can appear. Astronomers are fairly certain that up until four billion years ago, life was not possible on Earth. Collisions between the celestial bodies, which coalesced to form the earth, and the molten rock that covered its face probably prevented their formation.
But surprisingly, only 400 million years later, already there were bacterial colonies on the surface of the earth. These early life forms and the processes of photosynthesis they caused changed the texture of the Earth's atmosphere. Moreover, researchers claim that even 200 million years ago, the structure of the atmosphere already had evidence of thriving life.
If so, we must assume that a hundred million years or so, a surprisingly short time, is the amount of time needed to create life. The implication of this is that life is an expected and not exceptional phenomenon. Otherwise, there is no way to explain their formation so quickly.
Now we have to look at Mars, as it looked 4 billion years ago. It was a much hotter and wetter planet than it is today. It is quite possible, according to the evidence we have, that there were rivers, lakes and perhaps even large seas. If life is able to appear in a short time, it is possible that in the hundreds of millions of years that passed before Mars was a desolate desert, there was life there.
We will get more information about this exciting possibility when an intensive search for fossils on Mars is applied. This can be expected in the not too distant future.
Are there other planets like ours?
Solar planets containing organic matter and water are not that rare in the universe. George Weatherill from the Carnegie Institution in Washington developed detailed models for predicting the distribution of such planets. His conclusion is that a typical planetary system contains one or two stars where water and organic molecules may be present.
Alexander Walszan, a researcher from Pennsylvania, noticed planets with conditions similar to those on Earth, in a rather surprising place: around a pulsar, a star emitting electromagnetic radiation, left over from a supernova explosion. These planets are closer to their sun than we are to our sun. They appear to be too hot for life to exist, but there is also a more distant planet, more suitable for life.
The ongoing research is expected to find more and more such stars. We have reasons to believe that many planets rich in water and organic matter exist in the universe. Is it not expected that there will be life in them? In any case, the way to the actual discoveries of such a life is still far.
