Free Astronomy Magazine September-October 2019

11 ASTROBIOLOGY notice an abnormal abundance of oxygen and methane compared to atmospheric models for planets like ours in systems like ours. Although fluctuating, the disequilib- rium has protracted long enough to be the- oretically detectable from any point in the galaxy and beyond. If, somewhere out there, there is someone with adequate technology, he will already know that life forms exist on our planet. We said above that, in the absence of a re- plenishing supply of oxygen and methane, the two molecules would soon disappear: the Sun, with the help of oxygen, would eliminate methane from the atmosphere in just ten years; an M dwarf would take a cou- ple of centuries instead. Not knowing in what concentrations biosig- natures can be present in the atmosphere of another planet, searching for them around a star less efficient than the Sun at eliminating them could offer more chances for success. As we have seen, however, M dwarfs are not the ideal solution. Therefore, K dwarfs re- main. All the advantages of choosing this last spec- tral class have been treated in a theoretical study by Giada Arney of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, A n artist’s ren- dering of the future Thirty Meter Telescope and a diagram that shows how new technology developed at Cal- tech will work: a coronagraph blocks a star’s light, making or- biting planets easier to see and study. [NAOJ, Cal- tech/IPAC-TMT] A similar process is represented in the animation of the previous page. [NASA/JPL] SEPTEMBER-OCT