Svante Arrenhius proposed a new theory of the formation of life in 1906. According to him, life was not born on Earth but had arrived from space. According to him, unicellular organisms would have travelled the sidereal spaces for millions of years to reach the Earth. The push that would make them travel in space would be the radiation pressure of the starlight. Once on a planet, they could give rise to life and higher life forms guided by Darwinian evolution. The idea that led Arrenhius to these conclusions was the observation that terrestrial microorganisms could reach the stratosphere and reach space. It was therefore also possible that from a planet on which life was present, it had reached the Earth or other parts of the Universe. Arrenhius’ hypothesis is called panspermia (from the Greek, “common seed”). A few decades later, in the 1960s, Carl Sagan was attracted to this idea. To confirm the hypothesis of Arrenhius, microorganisms were found in the stratosphere. Sagan built a mathematical model based on the radiation pressure of sunlight and the gravitational force of the Sun and described, together with Josif S. Shklovskii, the results in a 1966 book: Intelligent Life in the Universe. If these two forces are equal, the organism remains in space. If the gravitational force is greater than the radiation force, the organism will fall onto the Sun. If the radiation pressure of light is greater than the gravitational force, the organism will move away from the solar system into the interstellar space. The model also provided the dimensions of these microorganisms, which would have had a radius between 0.2 and 0.6 thousandths of a millimeter, typical dimensions of the spores of fungi and bacteria. These microorganisms would have taken a few years to leave the solar system and a few tens of thousands of years to reach, for example, Proxima Centauri, the closest star. If a microorganism with a radius of less than two thousandths of a millimeter was close enough to the solar system, it would enter it, and in its motion, it could deposit itself on planets, such as the Earth. Sagan also calculated the distance from which the microorganisms that could have given rise to life on Earth left. They would have originated from some planetary systems at a distance of no more than six thousand light years. The next question was whether a microorganism could survive thousands of years in space and then, upon arriving on a planet, become active and spread throughout life. In the vicinity of the Sun, ultraviolet and X-ray radiation can destroy unprotected microorganisms; if they had found themselves inside a meteor, perhaps they would have been able to resist. Interstellar spores can resist cosmic rays for hundreds of millions of years. Another problem is that the probability of a microorganism falling on a planet whose dimensions are very small compared with the scale of the movement of the microorganism is very low. Large numbers of microorganisms are ejected into our galaxy over long periods of time.

Are We Extraterrestrials?

章节
发表日期：

2025年

查看全文

Antonino Del Popolo

摘要

Svante Arrenhius proposed a new theory of the formation of life in 1906. According to him, life was not born on Earth but had arrived from space. According to him, unicellular organisms would have travelled the sidereal spaces for millions of years to reach the Earth. The push that would make them travel in space would be the radiation pressure of the starlight. Once on a planet, they could give rise to life and higher life forms guided by Darwinian evolution. The idea that led Arrenhius to these conclusions was the observation that terrestrial microorganisms could reach the stratosphere and reach space. It was therefore also possible that from a planet on which life was present, it had reached the Earth or other parts of the Universe. Arrenhius’ hypothesis is called panspermia (from the Greek, “common seed”). A few decades later, in the 1960s, Carl Sagan was attracted to this idea. To confirm the hypothesis of Arrenhius, microorganisms were found in the stratosphere. Sagan built a mathematical model based on the radiation pressure of sunlight and the gravitational force of the Sun and described, together with Josif S. Shklovskii, the results in a 1966 book: Intelligent Life in the Universe. If these two forces are equal, the organism remains in space. If the gravitational force is greater than the radiation force, the organism will fall onto the Sun. If the radiation pressure of light is greater than the gravitational force, the organism will move away from the solar system into the interstellar space. The model also provided the dimensions of these microorganisms, which would have had a radius between 0.2 and 0.6 thousandths of a millimeter, typical dimensions of the spores of fungi and bacteria. These microorganisms would have taken a few years to leave the solar system and a few tens of thousands of years to reach, for example, Proxima Centauri, the closest star. If a microorganism with a radius of less than two thousandths of a millimeter was close enough to the solar system, it would enter it, and in its motion, it could deposit itself on planets, such as the Earth. Sagan also calculated the distance from which the microorganisms that could have given rise to life on Earth left. They would have originated from some planetary systems at a distance of no more than six thousand light years. The next question was whether a microorganism could survive thousands of years in space and then, upon arriving on a planet, become active and spread throughout life. In the vicinity of the Sun, ultraviolet and X-ray radiation can destroy unprotected microorganisms; if they had found themselves inside a meteor, perhaps they would have been able to resist. Interstellar spores can resist cosmic rays for hundreds of millions of years. Another problem is that the probability of a microorganism falling on a planet whose dimensions are very small compared with the scale of the movement of the microorganism is very low. Large numbers of microorganisms are ejected into our galaxy over long periods of time.