It’s not enough for it to be the right distance from its star: in order for liquid water to exist on its surface and for it to be considered habitable, a planet must also receive the right amount of ultraviolet radiation, which is necessary to allow the formation of the iochemical building blocks at the basis of life. This is indicated by the Italian study conducted by the University of Insupria in cooperation with the National Institute of Nuclear Physics, which narrows the circle of planets that are candidates for hosting extraterrestrial life. research, Connected On the arXiv website and published in the Monthly Notices of the Royal Astronomical Society, it shows that 75% of known stars are too cold to trigger these processes.

The researchers, led by Riccardo Spinelli of the University of Insubria, used NASA’s Swift space telescope to observe 17 stars hosting 23 planets in the habitable zone, i.e. the right distance to have liquid water. “Planets detected in the habitable zone of red dwarfs, which make up the majority of stars, do not receive enough ultraviolet radiation to trigger some of the processes that lead to the formation of the building blocks of life, such as RNA,” Spinelli notes.

“For these reactions to start, the star’s surface temperature must be at least 4,000 degrees, but 75% of the stars in the universe are much cooler.” “On the other hand, we know that too much ultraviolet radiation is harmful to life, because it damages DNA and destroys many proteins,” the researcher continues. So, around every star, there is a zone in which a planet receives enough ultraviolet radiation to stimulate the emergence of life, but not so much to destroy it: the study authors called it the “habitable ultraviolet zone” and it should overlap, at least in part, with what allows of liquid water.