Two conditions reveal fundamental to keep the molecular bonds, any that are, astrophysicists media and therefore to have a chance of finding in them the water molecule H2O temperature must not exceed some thousands of degrees so that collisions with atoms of the environment not too easily break the molecular bonds; gas must not be subjected to ultraviolet radiation that would threaten to destroy the molecules by fotodisociador effect. The water vapor, in galaxies, is diluted in a molecular hydrogen and helium gas. Its molecule is characterized as the of all the chemical species, by the absorption or emission of electromagnetic radiation giving rise to spectral stripes with a few wavelengths known, primarily in the infrared and millimeter intervals. But these stripes are very difficult to observe from Earth since, precisely these wavelengths of radiation that comes to us, are absorbed by the Earth’s atmosphere. Since it is precisely the water vapor from the atmosphere which causes this disturbing absorption. Even in the driest places, the majority of spectral rays of the steam of water are unobservable.

Therefore necessary to wait for the results of the various observatories onboard satellites, scheduled for the coming years, as the Observatory infrared space (ISO) of the European space agency or the more modest specialized satellite of NASA, to have an in-depth understanding of the abundance of water vapor in the cosmic gas. Away from the Sun: Comets and satellites of ice was therefore in this outer zone of temperature sufficiently low, beyond some UA, (6) where the water vapor could condense into ice. But grains of interstellar dust ice could also survive in his State, without never evaporate during the formation of the solar system. During collisions, to very small relative velocities, these beads were joined, is acrecionaron to each other to form the cores of comets, just as we see them today.