For a planet to be habitable, just as we conceive of life, various factors are necessary. To begin with, a planet with a precise life of energy, carbon, liquid water and an atmosphere. These conditions have a lot to do with the distance of the planet to its star. If it is too close or too far, high or low temperatures will prevent the existence of water in a liquid state.
Another essential factor is that the planet has a molten metal core. By turning around the star, the nucleus generates a magnetic field that protects the planet from X radiation and gamma radiation from the star.
It is also necessary to have a large satellite. In the case of the Earth, without the gravitational effect of the Moon, the inclination of the axis of rotation of our planet would have been modified considerably. This would have caused great climatic cataclysms.
Other essential conditions are to have sufficient gravity to retain the atmosphere; that the star of the planet has the appropriate life time to develop life, the ideal is a medium star like the Sun; the existence of nearby giant planets, whose enormous gravitational attraction can divert asteroids and protect the planet, and finally have an ideal situation in the Milky Way. It is best to be located far from the galactic center, where the harmful explosions of supernovae occur.
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