Astrobiology is a science that studies the origin, evolution and distribution of life forms in the universe, trying to find out if there are life forms born outside the planet Earth. This science in the past was also called bioastronomy or exobiology; these designations are still used by some authors.

Astrobiology involves worldwide a large number of researchers belonging to various disciplines: astronomy, biology, earth sciences, mathematics, science and technology of telecommunications, but also sociology and philosophy. The International Astronomical Union, which gathers all professional astronomers, has a section dedicated to astrobiology (Commission F3 Astrobiology), and there are Institutes of Astrobiology in several scientific institutions, such as NASA Astrobiology Institute, Centro de AstrobiologĂ­a.

Two international scientific journals deal exclusively with astrobiology: Astrobiology and International Journal of Astrobiology. Several professional research associations gather scientists involved in astrobiology; the main ones are The International Society for the Study of the Origin of Life – The International Astrobiology Society (ISSOL) and the European Astrobiology Network Association (EANA), which gathers astrobiology societies operating in Europe. In Italy there are some university teaching of astrobiology.

Historical notes

The idea that life can exist outside of planet Earth is very ancient. Already in ancient Greece philosopher Democritus argued that, since everything in the universe was made from atoms, and life itself was made from atoms, then life must exist in the whole universe. Democritus’ theories were also supported by later philosophers, such as Epicurus and Lucretius, while they were criticized by others, in particular by Aristotle, who supported the immutability and perfection of the heavens composed of ether, also arguing that each element (earth, water, air and fire) tends to its own unique center of motion, and therefore can not exist other worlds besides ours.

The Aristotelian-Tolemaic view of the universe then became the accepted idea of Christianity and was not questioned until the end of the Middle Ages and the Renaissance, when Copernicus’ heliocentric theory became popular. At the end of the XVI century Giordano Bruno affirmed the existence of infinite worlds arguing that the work of God could not be limited only to one world in the universe. In the following centuries the idea of plurality of worlds was supported by many philosophers and scientists, such as Descartes, Huygens (who affirmed the possibility that other planets could host life forms), Fontenelle and Voltaire. The latter wrote the novel MicromĂ©gas, which has as its protagonists beings from Sirius and Saturn, and is considered one of the earliest examples of science fiction.

At the end of the nineteenth century Schiaparelli observed Mars and described elongated structures he called generic channels, but considered by some astronomers as artificial channels, the work of an intelligent civilization. Great supporter of this hypothesis was Lowell, who published much in this regard and described extensively these channels, spreading the idea, long persisted, that Mars was inhabited. Only in the sixties, with the first space missions to Mars, new photos and maps of Mariner probes refuted the hypothesis of the channels and described the planet as arid and desert.

In the nineteenth century Darwin introduced the idea of evolution of life from simple organisms to complex species, while in the same period the birth of spectroscopy allowed to discover that in the universe are widespread the same chemical elements present on Earth, supporting the idea that planets could form around other stars. In the same years Pasteur showed that life is generated only from other life and not from inanimate things.

The debate on the origin of life on Earth in the following years went further, arriving to extreme hypothesis such as panspermia, which makes the hypothesis that terrestrial life forms were born elsewhere and then brought to our planet, in the form of spores pushed by sunlight to interstellar space as claimed by Kelvin and Arrhenius, or were voluntarily brought to Earth by spaceships, as proposed by Crick and Orgel. The hypothesis of panspermia was denied by Haldane and Oparin, who proposed that life was generated by a combination of chemical properties from organic molecules, without the need for external intervention. The experiment performed by Miller and Urey in 1953 showed that some amino acids could be formed from simple molecules such as hydrogen, ammonia and methane.

In the twentieth century, the invention of radio receivers and later the radio telescope brought new tools to the search for extraterrestrial life. Already in the twenties Marconi tried unsuccessfully to pick up signals from Mars. Later Cocconi and Morrison proposed to search for radio signals from other stars, as evidence of the existence of intelligent civilizations. In 1961 Drake developed an equation to determine the number of civilizations able to communicate. Shortly after the first SETI projects for the search of extraterrestrial life were born and in 1974 the first radio message to other civilizations was transmitted, followed by messages placed on the probes Pioneer and Voyager. Dyson instead described the possibility that an evolved civilization can create a sphere around its star to use its energy and proposed to search for signals in the infrared.

In recent decades, the discovery of exoplanets has led to new projects, which include spectroscopic analysis of the atmosphere of these bodies in search of oxygen, ozone and chlorophyll. In the solar system, research focuses on Mars and the satellites of Jupiter and Saturn, which may harbor microscopic life forms.

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