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[1] The spinning of our earth on its axis is stabilized by our very large moon; a moon that is of a size to create such stability is indeed rare. Our own resulted from a collision with a Mars sized planet. If our earth’s spinning was not regulated, then its axial tilt could change enough over time to make climate inhospitable to higher forms of living creatures.
[2] How much of the Earth's protective magnetic field is a result of that same large moon, and that magnetic field limits/nullifies a number of life withering effects like solar radiation, x-rays, cosmic rays, and others inhospitable to life being able to develop to the level of intelligence and civilization?
[3] And how about the plate tectonics comes from tidal effect of the same moon that makes such great surface relief common, without which so much of the surface would be below sea level?
[4] How about the relative sparseness of our own stellar neighborhood; doesn’t that factor make persistent bombardment from space by objects capable of destroying life in its nascent form long before intelligence evolves much less a factor than in more dense regions?
[5] And how about double stars (or triple stars), which are by far the most common situation; how does that impinge on the development of life and stable environments; vis-Ã -vis small planets with large moons or earth sized planets with stable orbits?
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Although I wish it were not the case, because of these known’s, and many unknowns, I suspect that civilizations capable of space travel are very rare compared to the number of stars at first blink which seem just right for basic life to just get started. To me, this means, some relatively low number of civilizations may have developed and their coming across each other, or conveniently communicating with each other will be a while in happening.
Actually, all your points are valid in the
what if category. This is sound. It is also factored in when using the Drake Formula. Frank Drake was right on and in his simple formula (I use it constantly), it does define easily the what ifs and what may be. Suffice to say, then, it is being quickly learned that Class G worlds are common and the Goldilocks Zone is a common denominator. This then infers that Drake is probably correct, and there are about 10,000 inhabitant systems like Earth and our solar system in the Milky Way Galaxy, our home.
Where they are and what they are is the question, of course.
Too, finally, with your suppositions, out of 120,000,000,000≥ stars in our galaxy, and only 10,000 with developed life, that is a tiny tiny percentage. or, √/.00012%.
Not much.....but its more than one.....
Good input. Thank you.
Robert
Thank you, but I can't completely go along with your answer. I don't mean to quibble but the data applied to the “Drake Formula” is arbitrary. When I enter my own calculations into Drake, mine look like this:
* = the number of stars in the Milky Way galaxy: 100 billion
(accounting for [5] above, this is a reasonable ball-park number)
FP = fraction of stars with planets around them: 50%
(depending on the odds of existing VS. not existing about half seems a reasonable number; expressing a fifty-fifty chance)
NE = number of planets per star ecologically able to sustain life: 0.5%
(sustaining life is the rub; even in our relatively safe region of space, the continuity of life [4] once started has been fraught with risk and could be terminated unexpectedly at any time)
F1 = fraction of those planets where life actually evolves: 70%
(assuming with enough time life beginning is inevitable and ubiquitous a high factor seems reasonable)
FI = the fraction of F1 that evolves intelligent life: 0.5% (If by intelligent we mean intelligence which survives long enough, enduring all the vicissitudes of severe climate change (a given) from all the many ways that can come about then 1/10th of fifty-fifty seems to be reasonable) Without a large moon to stabilize axis tilt [1][2] climate will be chaotic. A satellite of comparable size seems to be the most delimiting factor of all)
FC = the fraction of FI that communicates: 5%
(suggests a clear view of the heavens and an intention to communicate to hypothetical creatures beyond their own solar system in spite of the economic costs and political impingements) conditions on the planet can inhibit any interest in worlds beyond their own; [3] above. Life developing under-water - or under a thick atmosphere - regardless of a high intelligence, will lack incentive to communicate with creatures beyond their own world since they will lack awareness.)
FL = the fraction of the planet's life during which the communicating civilizations survives: 1/1,000,000th (10,000 years) (default number seems reasonable)
N = the number of communicating civilizations in the galaxy = 44 (43.75) civilizations
With such a small number of communicative civilizations existing and overlapping at any moment in time, we well might never find each other short of some faster than light travel. So in your final comment in bold, we definitely agree.
/SS/ American Horse - A.A. (Amateur Astronomer/60 years and counting)
