Lonelier and lonelier…

Life just got lonelier in our Galaxy.

According to a new study in the Monthly Notices of the Royal Astronomical Society (yes, I know, nobody reads that) the chances of complex alien life developing on other planets in our galaxy just got more unlikely.  It appears that an asteroid belt like the one we have in our solar system was essential for allowing life to develop on our Earth a couple billion years ago and for allowing life to flourish to the point where we humans have become the dominant species.  Moral: if you don’t have an asteroid belt, you don’t get complex life.

Over the years that astronomers have been listing the things that a solar system has to have in order for life to develop and flourish, more and more factors have been added to the list.  A planet has to have water on its surface and be just the right distance from its sun so the water can exist as a liquid.  It can’t be too hot or cold.  It has to have carbon-compounds to make the organic building blocks of life.  It can’t be slammed by asteroids too frequently or the nascent life will be wiped out.  It can’t be hit too infrequently either.  Astronomers are adding new factors all the time and a relatively new wrinkle is that a solar system has to have a large Jupiter-sized planet to keep the asteroids in line, yet early in a solar system’s life the planet has to be hit with enough outside material to bring the carbon compounds and the water that will nurture living forms.  It has to be pelted just enough–not too much, not too little.

It’s a complex scenario, and it’s getting more and more complex all the time.  Now we find out that asteroid belts appear to be rare in other solar systems.  This is preliminary data, mind you, and it could change as we learn more about other solar systems, but finding solar systems similar to ours which have all the factors going for them that our solar system has is increasingly unlikely.  What this means overall is that planets like Earth are getting even more rare in this galaxy.  Earth is odd, unusual, uncommon.  Notice I did not say unique.  The possibility of other “Earths” is still there, but that possibility is getting less and less.

I’ve said this before: we may be alone in this galaxy, or at least in the part of the galaxy we can see and examine with telescopes.  The attempts to find alien life such as listening for signals from outer space and sending probes to Mars and the moons of Jupiter to find microbial life are important, but don’t be surprised if they fail.  We may be alone.  Get used to it.

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