Free Astronomy Magazine November-December 2020

NOVEMBER-DECEMBER 2020 As we search today, the detection of oxy- gen in an exo-atmosphere does not then mean a wealth of multicellular organisms but may mean that some simple lifeform producing oxygen as a waste product might be responsible for what we detect. Phosphine, from our current understanding, falls into the same category as meth-ane and oxygen. Without some source to re- plenish it, it simply should not be detectable in the atmosphere of a rocky planet based on what we currently know of its chemistry. If Venus samples reveal a lifeform produc- ing phosphine (or any molecule!), Earth would go from being alone in the universe to the second planet in its own solar system. Technological sophistication aside, evolu- tion on two close planets with different his- tories and surface chemistries dramatically expands what exobiologists know to look for. But the ramifications of one or more new lifeforms will not be fully known until scientists are able to determine beyond all doubt that the lifeform is a product of Venus alone. You can, after all, buy Mars rocks − proof that the rocky inner planets have exchanged materials regularly over the history of the solar system. Consider just one aspect of Earth biology: if the DNA of a Venusian lifeform, if it has