Antoine Boutros - And finally the exciting historic moment came to be. For in last September scientists at the University of California announced the discovery of the first planet relatively close to Earth that possesses indicators providing a convincing example of what seems to be the most Earth-like planet “capable of being populated”. The planet was named Gliese 581 g and is located in the constellation Libra, at the center of our galaxy, the Milky Way. It orbits around the red dwarf star Gliese 581, which consists of a planetary system composed of five other planets (Gliese 581 e, b, c, d, f) but the fourth planet, the one in question, is the only one with potential to harbor life, according to scientists.

The planet is located 20 light years away from Earth, and has a mass 3.1 to 4.3 times Earth’s and its radius ranges between 1.5 to 2 times that of the Earth. It is thought to be a rocky planet with a surface gravity resembling that of planet Earth.

Its temperature varies between -12 and -31 degrees Celsius, which is enough to keep water, a necessity for life, in a liquid state, provided it exists. It is known that on Earth, extreme temperatures exist and that does not prevent the presence of life. Such temperatures vary between -70 degrees Celsius in the South Pole and over 148 degrees Celsius near hydrothermal vents at the bottom of the ocean where bacteria multiply.

The question now is: what are the requirements for a planet to be able to sustain human life or even be inhabited and then what are the possibilities of the presence of life on other planets?

It is necessary for there to be a solar system, meaning a central star around which one planet, or more, orbit. This planet should be at a moderate distance from its central star, meaning neither too close, like Mercury and the Sun, nor too far, like Jupiter. Among the primary requirements for life is the presence of liquid water and atmosphere. In other words, this planet should closely resemble Earth and this is what we have found in our new planet.  Therefore, once we find a solar system with a moderately distanced planet then we can start looking for elements of primitive, simple or intelligent life.

Ever since human beings became aware of their presence on Earth and in the Universe, a religious and philosophical concept, known as the Anthropic principle (from Anthropos, the Greek term for human being) emerged. It considers the human being as unique in this Universe and holds that the Earth alone is the center of existence. When Italian astronomer Galileo looked through his telescope for the first time and saw the rings of Jupiter, he realized that the Earth was not the centre of everything. When he noticed that Venus’ cycles were similar to the appearance and disappearance phases of the moon and its variations (until it becomes a full moon), he concluded that there must be an orbit around which this planet rotates. That meant that the Sun, not the Earth, was the center of our solar system. Thus, the concept of the centrality of the Earth collapsed scientifically, even though it did not completely vanish from the minds of people, even scientists. For example, Enrico Fermi, the famous scientist who was the first to succeed in creating an atomic reaction that later led to the making of the atomic bomb, used to say that had other worlds existed, they would have contacted us and shown themselves to us.    

On the other hand, scientist Jacob Bronowski cautioned that the evolution of life in other worlds in the Universe would not necessarily need to be similar to that on Earth. By extension, it is not unlikely that we might come across forms of life without being able to recognize them as such. They might be completely different to the forms of life on Earth and based on different foundations.

The disk of the Milky Way Galaxy is approximately 100,000 light years in diameter and in remote areas, on a clear summer night, it appears as a bright white cotton cloud inlaid with stars. Scientists estimate that it contains no less than 400 billion stars. If we assume that 10% of the galaxy resembles the Sun in terms of age and formation, then this means that there are 40 billion stars that are qualified to form a solar system. And if we consider that 10% of them are linked to planets located at moderate distances from them, therefore with moderate temperatures, then the possibility increases to 4 billion habitable systems.