This article, says 700 planets have been found outside our solar system, and five, were within the habitable zone of their stars and are candidates for life. Projected across the galaxy, there are a huge number of such habitable planets, roughly 2 billion. If you believe in panspermia, then rephrase that to be inhabited planets.
Inhabited does not, however, imply intelligent life.
Go back to my earlier blogs to learn more about panspermia, but in summary it means life has been scattered by some mechanism throughout the universe. Like the spores in The Invasion of the Body Snatchers, when they land on fertile ground, they spring into life, our one-celled progenitor being one such spore. Experience on Earth shows that this one-celled foremother had the amazing property of responding to changing and diverse environments, generating a plethora of successful mutations, i.e. living species.
The emergence of life on Earth from a single cell is an accepted scientific fact based on our knowledge of DNA. However the origin of the first cell is not understood and is as much a philosophical, religious question, as it is a scientific one. Atheists and humanists, who wish to be devoid of God, favor the theory of spontaneous generation, a modernized version of medieval black magic or voodoo where chemicals get sparked, and like the Frankenstein monster, begin to jump for joy with life. The idea was first proposed by Darwin after following his trail of evolution back to the first cell, then realizing that his theory was boxed off. In those days, there was no knowledge of DNA, nor the tool of statistics to guide him, so he can’t be blamed for not recognizing the mathematical impossibility of a cell arising spontaneously from chemicals. His modern day followers, however, can only blame their hardheadedness for continuing down the path of spontaneous generation even when they admit it is mathematically impossible and only came to be through a miraculous accident (minus the miracle, of course).
Francis Crick, the discoverer of DNA, on seeing the complexity of what he had found, e.g. a ten foot, billion particle sting of DNA from one single microscopic cell, realized that the random emergence of life was mathematically impossible and offered the alternative of panspermia, fully functional spores of life scattered throughout the universe, taking hold anywhere and everywhere possible. This defers solving the mystery of the original cell to some future time when we have information about extraterrestrial life, and until then, God, aliens, and magic on equally footing as the source of the first cell.
Let’s assume panspermia is right and that all life in our galaxy has the same genetic forbearers. Then what kind of life can we expect to find on the five planets that have been identified outside our solar system?
First let’s digress and note that with panspermia, it is possible that marginal planets could also evolve life, at least microbe forms, since they don’t have to waste a lot of time sparking life from inanimate chemicals. I.e., there could be several times the 2 billion habitable planets first estimated.
The five planets candidate planets have been chosen because they lie in the habitable zone of their stars, meaning water can exist as liquid on their surfaces.
Two, Kepler 22b and HD85512b, are estimated to have temperatures greater than 150 degrees Fahrenheit (70 Celsius). This seems too high for life; yet on Earth, life has been found at high temperatures near volcanic vents in the ocean floor and deep in the Earth’s crust. In fact, some scientists propose that these are the places where life first spontaneously generated. I can’t tell you whether they read Mary Shelley in their impressionable youth. In short, our experience on Earth shows that these two planets are not too hot for microbial life.
Size matters: All of the planets have greater mass than Earth, two, Gliese 667Cc and Gliese 581d are massive. Mass might influence the evolution of intelligence, compressing life forms into stocky, thick legged creatures that never become bipedal, never have hands, and hence are never able to make advanced tools, a factor that might limit their intelligence. Even if it doesn’t limit intelligence, it probably would prohibit them from escaping gravity and becoming space travelers.
This leaves Gliese581g, 20 light-years away, having mass about 3 times Earth’s and, with an ESTIMATED AVERAGE temperature just below freezing, liquid water possible is possible in sub-climates. Keep in mind that in our geologic past we have been “Snowball Earth”, frozen from pole to pole, leaving the water below the ocean ice cap as the only place where life could exist. We are currently in a million year long ice age. Major portions of Earth have been under a mile thick ice cap 80% of the time during this ice age. Even on Earth, the temperate climate we know is rare. Gliese581g could be very much like Earth.
Of the five, it seems to have the best chance, maybe even a good chance, of evolving tool-makers, but at three times the mass of Earth, gravity may lock them to their planet, something we should consider before landing there.