Where Are They? Part 3

In the first two entries in this series of brief examinations of the difficulty of traveling in outer space to new planets and stars and worlds, I looked at how difficult it is for humans to travel in outer space (we’ve only just made it to the moon), and whether the knowledge of the ability to travel to other stars and their planets really exists at all.  Is such knowledge universally available, or are we condemned to travel long distances in spacecraft at well below the speed of light?

In this post, I want to look at the development of life on a fledgling planet and ask the question, what does it take for intelligent life to develop?  In fact, I want to go back not only to the development of life, but further, to the birth of the planet itself.  What conditions are necessary for a planet to develop life?  This will be a tricky question to ask properly because we have only one known example where such conditions have arisen, the Earth, and we can’t be sure that what happened on Earth is a reasonable example for life developing elsewhere.  But what the hell, let’s take a look.

Others have tried to estimate the probability of life on other worlds, and the Drake equation is one such estimate.  But the Drake equation is concerned with estimating what fraction of planets out there are broadcasting signals into space, a point in evolution we have already reached.  As with any examination of the presence of life on other worlds, estimates have to be made when entering data into the Drake equation, and in reality, we have no idea how accurate those estimates are.  I’m more interested in trying to find out what percentage of planets that eventually coalesce into a physical body from the dust surrounding a newly-ignited star will eventually go on to develop intelligent life that can leave the bonds of the planet and fly around.  Let’s take a look at some of the factors that have to exist before this can happen.

Over the past several years I’ve jotted down a number of factors that have been proposed as essential for the development of intelligent life here on Earth, and, with a little bit of luck, might be necessary for life to develop on another heavenly body.
1.  A stable sun: the star around which such a planet orbits can’t get too hot or too cold, or it could halt development of life altogether.  (Earth’s sun has gone through cooling and heating phases, but never to a degree that baked or froze the planet, killing life completely.)
2.  The planet has to develop at just the right distance from the star.  The so-called “Goldilocks” zone.
3.  There has to be water on the surface.  Not just water, but liquid water, liquid because life can’t develop in steam or ice.
4.  The planet has to have an oxygen/nitrogen atmosphere.  Granted, life can develop in the absence of oxygen, and probably did on Earth, and those microscopic life forms did produce the oxygen in our atmosphere, but it most likely oxygen will be required for intelligent life to develop.
5.  The presence of oxygen in the atmosphere implies ozone in the upper atmosphere to protect the life forms on the surface from too much ultraviolet radiation.
6.  A magnetic field surrounding the planet.  This implies a liquid iron core and traps cosmic rays and other injurious stuff from outer space.
7.  Another planet in the same star system that is large enough to clear much of the excess debris around the star to prevent too much from bombarding the nascent planet.
8.  Yet, some bombardment is essential to bring all the stuff (like water) to the new planet that life will require.  Not too much, not too little.
9.  A large moon that provides a gravitational tug on the planet, inducing tides in the large bodies of water, as well as on the land masses, pulling and pushing them around in just the right way.
10.  The planet should be in a near circular orbit so that the radiation it receives from its sun is relatively constant.  Not too hot, not too cold.
11.  Other planets in the same system have to be in near circular orbits to prevent them from sending debris toward the newly-formed planet, and preventing their gravitational field from pushing the planet into an odd orbit, or even knocking it out of its solar system altogether.
12.  Tectonic activity to keep the developing life in a constant state of evolution.  Stagnation is the death-knell of advancing development.
13.  Periodic extinctions, whether caused by an asteroid strike, volcanic activity, the cooling of the central star, or other factor, to, as in #12, keep the development of life going.  Or, to put it more simply, everything has to be shaken up from time to time.

In so many of these factors, not only are they essential in an absolute or qualitative sense, but in a quantitative sense too.  Not too much, not too little.  Earth got just the right amount of some things—just the right amount of oxygen, a sun neither too hot or too cold, just the right size moon, and so forth.  That’s just going to complicate the calculations.

Now, with all these factors in mind (and there may be more we don’t know about), can we make any reasonable calculation as to what proportion of planets in our galaxy fit this profile?  Are there other planets out there that could have developed life like ours?  To make that calculation, we have to ask what proportion of planets meet each characteristic.  That’s impossible to do right now, so we have to estimate.  Such estimates may be way off, but let’s give it a try.  Let’s assume the simplest situation (and probably an overestimate), that each planet has a 1 in 100 chance of having each characteristic.  This works out to 1/100 to the 13th power, or 10 to the −26 power.  That says that only one planet out of 10 to the 26th has all the characteristics needed for life to develop.  It is estimated that around one hundred billion planets exist in the galaxy.  That’s 10 to the 11th power.  Okay, make it 10 to the 12th.  Clearly, even if we use a serious overestimate to the chances of any characteristic happening on a developing planet, we’ve just eliminated not only the possibility of life developing on another planet, but on our own too.  We shouldn’t even exist.  Yet, there’s good evidence these characteristics are essential.  We can’t just drop two or three.  The numbers just don’t add up.

So, where are we?  Those numbers do give one possible explanation to Enrico Fermi’s famous paradox, but they are such an overestimate it’s hard to know if that’s the right explanation or not.  It is possible that life could develop on other planets in situations we’re not familiar with, after all, we’re using Earth as an example and that may not be the most judicious model.  Are we freaks in one way or another?  Are we alone?  You be the judge.

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