Free Astronomy Magazine November-December 2014

ASTROBIOLOGY is inherited from the interstellar medium −that is to say, the clouds of gas and dust from which the systems themselves form and evolve. At first glance it may seem like a trivial difference, as the important thing is that there is water. But if the amount is determined by local conditions, then this can vary significant- ly according to the properties of a given protoplanetary disk and of the star that evolves at its centre. In molecular clouds where stars and planets form there is certainly water, ob- viously in the form of ice, given the very low temperatures. The question is whether that water survives the radiation flux from the stars it ends up orbiting, or if it is being destroyed (as a result of the separation of hydrogen from oxygen) to then be regener- D iagram of the solar system’s formation, em- phasizing the preservation of the primordial water ice during the various stages leading from the protosolar cloud to the fully formed system. [Bill Saxton, NSF AUI/NRAO] Left, a typical sunset over the sea −an image that from today takes on an added meaning, given that much of that water, perhaps half, is older than the star that lights it. ated through mechanisms and quantities dependent on local physicochemical prop- erties, different from those typical of inter- stellar clouds. Despite much research in this area, so far there has been no way to un- derstand if the water of our solar system was formed at the same time with it or if it is older, but some astronomers, led by Ilsedore Cleeves (Uni- versity of Michigan), have recently pro- posed an original so- lution to this issue, based on the ratio between the abun- dance of heavy water (D 2 O) and the abun- dance of normal water (H 2 O). The for- mer is characterized by the presence of deuterium, an iso-