The Planetary Habitability Laboratory (PHL), a virtual institution directed by astrobiologist Abel Méndez, from the University of Puerto Rico, in Arecibo, maintains a database in which potentially habitable worlds are collected. that have been detected in the Milky Way. These objects arouse the interest of researchers because they are located at the right distance from their star, in an area where it is neither too cold nor too hot, so that they could harbor water in a liquid state on their surface and, with it , maybe life. Among the almost 4,000 exoplanets whose existence there is no doubt, the PHL has cataloged 49 located in this region; among them, 16 similar to ours.
At the moment, these few are known, but, based on the data collected by the Kepler space telescope, a team of astronomers coordinated by Erik Petigura, of the California Institute of Technology, has calculated that only in our galaxy there could be 40,000 million planets the size of the Earth in orbit around stars similar to the Sun and red dwarfs, smaller than the star king. The possibilities that some – or many – of them have developed organisms seem overwhelming, but a new study promoted by Edward W. Schwieterman of the Department of Planetary Sciences at the University of California, Riverside, argues that it is better not get too excited and that astronomers should in fact rethink their estimates of the number of extrasolar worlds in which something more complex than a microbe could thrive.
Between the heat and the toxicity
In essence, what Schwieterman and his collaborators have discovered is that a buildup of toxic gases in the atmospheres of most of these worlds would greatly reduce the chances that, for example, animals would develop there; at least as we know them.
As explained in an essay published in The Astrophysical Journal , carbon dioxide plays a determining role in this phenomenon. This compound contributes to generating the so-called greenhouse effect, fundamental so that the temperature on the planets farthest from their star does not drop too much; otherwise its surface would freeze. However, it can be very damaging.
“For water to remain in a liquid state at the outer limit of what has been considered until now the habitable zone of a system, a planet would need to have tens of thousands of times more carbon dioxide than the Earth has today Schwieterman, whose group has used computational modeling to study gas shells and interactions between light and molecules on a wide variety of worlds, says in a statement. “We are talking about something that goes far beyond the levels that are considered toxic to animal life on Earth,” he adds.
“It is the first time that this type of study takes into account the physiological limits of living beings on our planet to try to predict their possible distribution in other areas of the universe,” emphasizes biogeochemist Timothy Lyons, co-author of this work. “Our results show that, if we take into account the traditional definition of a habitable zone, the ecosystems that can be found on Earth simply could not exist in most of those regions of other systems,” he says.
Referencia: A Limited Habitable Zone for Complex Life. Edward W. Schwieterman et al. The Astrophysical Journal (2019). DOI: doi.org/10.3847/1538-4357/ab1d52
Image: ESO / M. Kornmesser
