"Rare" is a relative term. Are galaxies rare because they're millions of light-years apart? Or are they common because there are billions and billions of them? It depends on your perspective.
The really interesting question is whether there is any extra-terrestrial life at all, or extra-terrestrial intelligence. If Earth is the only planet of its kind in the entire universe, then that's really something to ponder.
OK, let's take a good look at just what is necessary for a world to be capable of supporting an intelligent, technological civilization:
1. A star not in the central galactic bulge (most of which are "metal poor", meaning they are incapable of spawning Earthlike worlds) - ours in nicely tucked away in a spiral arm. 2. A star not in the path of sprays of lethal Gamma radiation from the galaxy's central black hole (which disqualifies maybe 1/5th of the stars in the Milky Way) 3. A non-variable star (the majority of stars are variable). 4. A planetary system capable of supporting stable orbits (most aren't). 5. A planetary system with no worlds of Jupiter mass near to the star (Most of the discovered systems have such worlds. Ours is a rarity in that it does not.). 6. An inner planetary system cleared of small bodies, protoplanets, comets, etc., which requires a Jupiter sized world to be located immediately outside the Habitable Zone (just like our own Jupiter). 7. A rocky planet within the star's habitable zone (in which water can exist on the surface in all 3 states - solid, liquid, and gas). 8. A planet with a rotating liquid core, creating a dynamo, and thus a magnetic field about the world (shielding the surface from harmful radiation). 9. A planet whose crust is broken into plates, allowing for plate tectonics (thus recycling the surface material and preventing the world from ending up like Venus, a sterile, superheated wasteland). 10. An atmosphere dense enough to allow liquid water to exist on the surface, yet not so dense as to crush all potential lifeforms. 11. Water. Not so trivial as you might expect. Astronomers to this day have no idea how and why the Earth possesses so much water. Every current model and theory says it shouldn't be there. 12. A large moon (just like ours), which stabilized the planet's axis, preventing wild and unpredictable extremes of climate - everything from the oceans occasionally boiling away to the surface being encased in ice from pole to pole. 13. An interstellar environment conducive to billions of years of tranquility. I.e., no nearby supernovae for the lifetime of the system. All indications are that our own solar system has somehow (I almost wrote "miraculously") avoided being in the vicinity of an exploding star for its entire 4.5 billion year history. That alone makes us practically unique in the galaxy. 14. A star whose radiation peaks at a wavelength between 400 and 500nm, which allows for photosynthesis to occur (this alone rules out a good 90% of the stars in the galaxy).
I could easily go on, but you get the idea. All indications point to our world being either unique, or at most one of maybe a dozen such, in the entire Milky Way.
We absolutely are special, especially if biological macroevolution occurred, given that it is so improbable that this would happen before the sun ceased to be a main sequence star that evolution is evidence that God exists.
7 comments:
"Rare" is a relative term. Are galaxies rare because they're millions of light-years apart? Or are they common because there are billions and billions of them? It depends on your perspective.
The really interesting question is whether there is any extra-terrestrial life at all, or extra-terrestrial intelligence. If Earth is the only planet of its kind in the entire universe, then that's really something to ponder.
This isn't saying much. It would be a bigger bang if an astronomer were to question Copernican principle.
Where's Bob P., my favorite armature astronomer comments?
Where's Bob?
I've been busy with the birth of my first grandson (taking care of his 3 year old "big sister") on Tuesday!
Don't worry - I'll weigh in eventually.
OK, let's take a good look at just what is necessary for a world to be capable of supporting an intelligent, technological civilization:
1. A star not in the central galactic bulge (most of which are "metal poor", meaning they are incapable of spawning Earthlike worlds) - ours in nicely tucked away in a spiral arm.
2. A star not in the path of sprays of lethal Gamma radiation from the galaxy's central black hole (which disqualifies maybe 1/5th of the stars in the Milky Way)
3. A non-variable star (the majority of stars are variable).
4. A planetary system capable of supporting stable orbits (most aren't).
5. A planetary system with no worlds of Jupiter mass near to the star (Most of the discovered systems have such worlds. Ours is a rarity in that it does not.).
6. An inner planetary system cleared of small bodies, protoplanets, comets, etc., which requires a Jupiter sized world to be located immediately outside the Habitable Zone (just like our own Jupiter).
7. A rocky planet within the star's habitable zone (in which water can exist on the surface in all 3 states - solid, liquid, and gas).
8. A planet with a rotating liquid core, creating a dynamo, and thus a magnetic field about the world (shielding the surface from harmful radiation).
9. A planet whose crust is broken into plates, allowing for plate tectonics (thus recycling the surface material and preventing the world from ending up like Venus, a sterile, superheated wasteland).
10. An atmosphere dense enough to allow liquid water to exist on the surface, yet not so dense as to crush all potential lifeforms.
11. Water. Not so trivial as you might expect. Astronomers to this day have no idea how and why the Earth possesses so much water. Every current model and theory says it shouldn't be there.
12. A large moon (just like ours), which stabilized the planet's axis, preventing wild and unpredictable extremes of climate - everything from the oceans occasionally boiling away to the surface being encased in ice from pole to pole.
13. An interstellar environment conducive to billions of years of tranquility. I.e., no nearby supernovae for the lifetime of the system. All indications are that our own solar system has somehow (I almost wrote "miraculously") avoided being in the vicinity of an exploding star for its entire 4.5 billion year history. That alone makes us practically unique in the galaxy.
14. A star whose radiation peaks at a wavelength between 400 and 500nm, which allows for photosynthesis to occur (this alone rules out a good 90% of the stars in the galaxy).
I could easily go on, but you get the idea. All indications point to our world being either unique, or at most one of maybe a dozen such, in the entire Milky Way.
Thanks Bob,
Blessings to you and your grandson.
We absolutely are special, especially if biological macroevolution occurred, given that it is so improbable that this would happen before the sun ceased to be a main sequence star that evolution is evidence that God exists.
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