Free Astronomy Magazine January-February 2015

times that pres- ent on Earth, with all that follows from the astro- biological point of view. The opti- mism spread by this last work has almost disappea- red in mid-De- cember, when on Astrobiology Mag- azine were made public the results of a series of com- puter simulations produced by two researchers of the Uni- versity of Washington, Ro- drigo Luger and Rory Barnes, that pretty much put an end to the chances of habitability on red dwarfs’ planets. In fact, the two UW researchers underlined an aspect rather neglected so far: the time required by a red dwarf to become a fully-fledged star (i.e. for entering the so-called “main sequence”), after hav- ing gone through the turbu- lent phases of its long infan- cy. This timescale is crucial for the purposes of habitability of planets, since while the latter need from few millions to tens of millions of years to completely form, red dwarfs need hundreds of millions of years, and at the end of that phase they are 10 to 100 times brighter and, hence hotter than they will be after ente- ring the main sequence. Consequently, the planets that end up or- biting the habitable zone at a later stage will remain exposed for a very long time to a flow of heat sufficient to raise the atmo- spheric temperature to hundreds or even thousands of degrees centigrade, with re- sultant total evaporation of any oceans present on the surface. At that point it is inevitable the formation of a global green- house effect, capable of pushing the atmo- spheric pressure towards values which are hundreds or thousands of times higher than those on Earth. In other words, are created environmental conditions more similar to those of Venus than those of our planet. But that's not all. In fact, a considerable fraction of the energy emitted by red dwarfs is in the form of X-rays and UV; a radiation that has a devastating effect on the water molecules that go up higher in the atmospheres of the planets located at a short distance from the source. The molecules break up, freeing the atoms of hydrogen and oxygen, which, at the high temperatures to which they are sub- jected tend to reach the escape velocity and disperse in space. Since this occurs more frequently for the lighter hydrogen, atmospheres end up being dominated by molecular oxygen (O 2 ), and although this element is useful for life, if it is too much it becomes dan- gerous. In the event of being possible to directly analyze the atmospheres of these planets (feasible within a few years) we would have the illusion of the presence of life, in being oxygen one of its possible re- vealing elements. The risk is to lose a lot of time in further investigation, which would invariably produce negative results. In con- clusion, the search for extraterrestrial life around red dwarfs is in effect beneficial for the currently available technologies, but chances are that it will not lead to any- thing, in the sense that within the habit- able zones of those stars could well exist only planets made forever unlivable by the turbulent infancy of their stars. n