An international group of scientists from various fields of science, led by Dr. Dirk Schulze-Makuch from the University of Washington, has developed a scale for assessing the likelihood of planetary habitability. One system (ESI) considers the degree of similarity of the planets to the Earth, the other (PHI) takes into account various factors.
So, when evaluating a planet regarding the possibility of biological life on it according to the ESI system, the size and density of the planet, as well as its location in relation to the star, are taken into account.
When ranking according to the PHI system, scientists take into account factors such as the presence of the atmosphere and magnetic field, surface structure (rocky or aquatic environment in a frozen state), the presence of energy emanating from a star or from processes in which the gravitational effect of other objects can heat the planet …
Another important factor in assessing the probability of life on the planet is the presence or absence of vital chemical elements to reproduce the corresponding reactions.
Based on the ranking systems created, the best conditions for life according to ESI are the Earth, and outside the solar system - the exoplanet Gliese 581g in the constellation Libra. According to the PHI system, the places, respectively, were distributed as follows: in the first place is the satellite of Saturn Titan, in the second - Mars, and in the third - Europa, the satellite of Jupiter.
In total, experts name 16 planets on which the detection of life forms is likely.