A few hundred thousand billion free-floating life-bearing Earth-sized planets may exist in the space between stars in the Milky Way. So argues an international team of scientists led by Chandra Wickramasinghe, Director of the Buckingham Center for Astrobiology at the University of Buckingham, UK. The scientists have proposed that these life-bearing planets originated in the early Universe within a few million years of the Big Bang, and that they make up most of the so-called “missing mass” of galaxies.
Since 1995, when the first extrasolar planet was reported, interest in searching for planets has reached a feverish pitch. The 750 or so detections of exoplanets are all of planets orbiting stars, and very few, if any, have been deemed potential candidates for life. The possibility of a much larger number of planets was first suggested in earlier studies where the effects of gravitational lensing of distant quasars by intervening planet-sized bodies were measured.
Recently several groups of investigators have suggested that a few billion such objects could exist in the galaxy. Wickramasinghe and team have increased this grand total of planets to a few hundred thousand billion (a few thousand for every Milky Way star) - each one harbouring the legacy of cosmic primordial life.
Are we the lone sentient life in the universe? So far, we have no evidence to the contrary, and yet the odds that not one single other planet has evolved intelligent life would appear, from a statistical standpoint, to be quite small. There are an estimated 250 billion (2.5 x 10¹¹ ) stars in the Milky Way alone, and over 70 sextillion (7 x 10²² ) in the visible universe, and many of them are surrounded by multiple planets.
Meanwhile, our 4.5 billion-year old Solar System exits in a universe that is estimated to be between 13.5 and 14 billion years old. Some experts believe that there could be advanced civilizations out there that have existed for 1.8 gigayears (one gigayear = one billion years).
The odds of there being only one single planet that evolved life among all that unfathomable vastness seems so incredible that it is all but completely irrational to believe. But then "where are they?" asked physicist Enrico Fermi while having lunch with his colleagues in 1950.
Fermi reasoned, if there are other advanced extraterrestrial civilizations, then why is there no evidence of such, like spacecraft or probes floating around the Milky Way. His question became famously known as the Fermi Paradox. The paradox is the contradiction between the high estimates of the probability of the existence of extraterrestrial civilizations and yet the lack of evidence for, or contact with, any such civilizations.
Given the extreme age of the universe, and its vast number of stars, if planets like Earth are at all typical, then there should be many advanced extraterrestrial civilizations out there, and at least a few in our own Milky Way. Another closely related question is the Great Silence, which poses the question: Even if space travel is too difficult, if life is out there, why don't we at least detect some sign of civilization like radio transmissions?
Milan Cirkovic of the Astronomical Observatory in Belgrade, points out that the median age of terrestrial planets in the Milky Way is about 1.8 gigayears greater than the age of the Earth and the Solar System, which means that the median age of technological civilizations should be greater than the age of human civilization by the same amount. The vastness of this interval indicates that one or more processes must suppress observability of extraterrestrial communities.
Cirkovic believes that highly efficient city-state type of advanced technological civilizations could easily pass unnoticed even by much more advanced SETI equipment, especially if located near the Milky Way rim or other remote locations.
Spurce: Wickramasinghe NC et al (2012). Life-bearing primordial planets in the solar vicinity. Astrophysics and Space Science; DOI 10.1007/s10509-012-1092-8
The Daily Galaxy via Springer journal Astrophysics and Space Science
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