A group of international astronomers and astrobiologists have published new research that assesses the possibility of complex life on other worlds. Their calculation in the Milky Way alone is staggering: 100 million worlds in our home galaxy may harbour complex alien life. One. Hundred. Million.
It is a lot — although maybe a bit disappointing when you consider that a) there are 17 billion Earth-sized worlds in our galaxy alone and b) these worlds are likely to be too far away from us (unless we can get a warp drive.) Also keep in mind that, according to the authors, "this study does not indicate that complex life exists on that many planets [...] only the conditions to support [complex alien] life."
But, even with those considerations in mind, I find their estimation impressive. Especially when you consider that this is only one galaxy — and there are 500 billion of them in the Universe.
The possibility of evolution of complex life in other planets
Their research supports "the view that the evolution of complex life on other worlds is rare in frequency but large in absolute number", and it contains the first plausible "assessment of complex life in the Universe using empirical data."
It's an assessment that comes from necessity. The search for worlds that may contain life is now the most important field of investigation in astronomy and perhaps the most important field in science, period. The discovery of worlds that can support complex life is not only vital for our long-term survival as species, but also the key to one of the most transcendental questions we face as species: Are we alone in the Universe?
To make their calculations, a team led by Louis Irwin — from the Department of Biological Sciences, University of Texas at El Paso — have developed a new index called the Biological Complexity Index (BCI), which ranks planetary bodies — including moons — based on the features discovered by our current technology. According to the paper, the index is "designed to provide a quantitative estimate of the relative probability that complex, macro-organismic life forms could have emerged on other worlds."
They believe that only 11 of the more than 1700 planets so far discovered in the Milky Way have a higher BCI than the Jupiter's moon Europa. That seems like nothing but, when you take into consideration the estimation of worlds in our home galaxy, "the total of such planets could exceed 100 million in our galaxy alone."
The paper was published in Challenges of Astrobiology by Louis Irwin — from the Department of Biological Sciences, University of Texas at El Paso — Abel Méndez — from the Planetary Habitability Laboratory, University of Puerto Rico at Arecibo — Alberto G. Fairén — from the Department of Astronomy, Cornell University — and Dirk Schulze-Makuch — from the Center of Astronomy and Astrophysics, at Technical University Berlin.