Abstract Details
| Name: Margarita Safonova Affiliation: Indian Institute of Astrophysics Conference ID: ASI2015_363 Title : Age aspects of habitability Authors and Co-Authors : Yu. A. Shchekinov (Department of Space Physics, SFU, Rostov on Don, Russia), J.~Murthy (Indian Institute of Astrophysics, Bangalore, India), Anuj Jaiswal(IIT, Delhi) Abstract Type : Poster Abstract Category : Stars, The Milky Way Galaxy and its neighbours Abstract : Is age of the planet important for its habitability? If we define habitability as the ability of a planet to develop life, then probably not. After all, life on Earth has developed within only 800 Myr after formation---the carbon isotope change detected in the oldest rocks indicates the existence of already active life at least 3.86 Ga (Gyr ago), at the end of the period of late heavy bombardment. If, however, we define habitability as our ability to detect life on the surface of extrasolar planets, then age becomes a crucial parameter. Earth became visibly habitable only about 750--600 Ma when the planet emerged from the one having a simple biota to a planet with diverse complex life (at ~ 540 Ma) capable of changing the environment enough to be noticed from space. Mars, for example, can still be inhabited at present (primitive subsurface biota) but unless the habitability is a global planetary phenomenon, it would remain undetectable. The importance of planetary age for detectability of life as we know it follows from the fact that the primary process, the photosynthesis, is endothermic with an activation energy higher than temperatures in habitable zones. Photosynthesis is currently the only known to us process that can provide sufficient energy to change the global planetary properties. We show that the onset of photosynthesis on planets in habitable zones may take much longer time than the current planetary age. The knowledge of the age of a habitable planet is important for developing a strategy to search for exoplanets carrying complex (developed) life--- many confirmed habitable planets are too young (orbiting Pop~I stars) and may not have had enough time to develop and/or sustain life. We discuss recent observational exoplanetary data from this point of view and suggest that recently discovered EMP stars (belonging presumably to an intermediate Pop~II.5 stars) seem to be good candidates for direct detection of orbiting Earth-size rocky planets in the IR and sub-mm wavelengths. In general, IR and sub-mm observations of rocky planets orbiting low-mass old stars seem a promising way to trace biogenetic evolution on exoplanets in solar vicinity. Such planets have had sufficient time to develop life provided they are located within a habitable zone. |