You’re looking in the wrong direction. It’s not a matter of how many planets we have to work with; it’s a matter of conditions for, and probabilities of, a self-replicating, self-diagnosing, self-repairing, self-fueling, Von Neumann entity.
Knowing that, the parameters you have to work within are MUCH better understood.
Dear FR friend. There is no definitive study on the probability of life elsewhere in the universe because no one has observed such life or its absence anywhere else, yet, and no one has been able to duplicate to any significant degree the “spark of life” which apparently occurred here on earth. However, it is notable that within very recent history scientists debated the probability of exo solar planets and many determined that there was a high probability that no other systems had planets, or that the occurrence of planets was very rare. You are quite correct that I am not an astro-physicist or a biologist or even a mathematician. However, we all can apply common sense and what received knowledge we have to arrive at our own opinion regarding the “probability” that a scientific theory is correct. As you know, we now realize the probability is for the existence of billions of exo solar planets. You can tell me I’m looking in the “wrong direction” but as a starting point, to discuss exo solar life we have to have exo solar planets. I’m merely pointing out to you that a few years back the work of these scientists might be a non starter if it was believed there were no exo planets. Now we know there are billions (most likely). Therefore we expect billions of exo planets in habitable zones of their stars. I submit to you that the scientists producing this report lack a reasonable basis for the accuracy of their probability analysis, because just as we now know previous assumptions about exo planets were based on inadequate knowledge, I submit there is a lack of knowledge presently regarding how and how often self replicating life occurs throughout the universe. Further, I pointed out that the authors for all their scientific credentials wrote a description of their work which refers to the lifeless conditions we observe everywhere. I noted that our main observations of life are right here on earth, and further, no one expected that the other solar planets presently harbor life. As regards exo planets we absolutely don’t have data on the occurrence of life on exo planets in habitable zones therefore I conclude the authors’ statement that we observe an absence of life everywhere else in the universe to reflect exactly the type of unscientific, out of their field guesswork to which you so strongly object. Their statement as to observation of life or its absence elsewhere, which they stated was the observation they were comparing to their probability study, was meaningless. This would have been like Christopher Columbus stating Pre 1492 that he was sure there were no inhabitants in the New Worlds he wished to discover, and that this comported with our lack of observation of such inhabitants, there having been no such observations one way or the other. Finally, reference to “Von Neumann” usually refers to self replicating machines or software. Of course you can apply the concept to biological entities, but we did not need Von Neumann to know biological entities are self replicating therefore the concept behind his work was never intended to be applied to biological entities or the manner or probability that they come into (initial) existence.