"Bottlenecks on the Road to Intelligence"

[blike]

I came across some interesting thoughts regarding extraterrestrial intelligence in the universe.

 

Bottleneck No. 1

 

The host star must be of the right variety in order to provide temperatures for a planet for billions of years. It must not belong to a binary or multiple star system (which eliminates two-thirds of stars), since planets with circuluar orbits cannot form there. Also, it must be of the right size. A star much smaller than the sun would require the planet to orbit closer in order to be in the habitable zone where water could exist as a liquid, but this would create tidal forces that would slow its rotation, causing it to cook on one side (as with Mercury). A star much larger than the sun would burn itself out before an intelligence civilization could arise. Even without the tidal effect problem, a star must fall in the range between 0.83 and 1.2 solar masses in order for an orbiting planet to avoid either a runaway greenhouse effect, as on Venus, or a permanent ice age, as Mars would experience if it had more water. (Michael h. Hart, "Atmospheric Evolution, the Drake Equation and DNA: Sparse life in an Infinite Universe," Cambridge, England 1995)

 

Bottleneck No. 2

 

The host star must begin its life surrounded by a protoplanetary disk (perhaps half of single stars do), and this disk must be the sort that is short-lived and small. Planets with medium or massive disks are doomed to spiral their way into their host stars. (Jeffery Winters, "Planets by the Dozen," Discover 1997)

 

Bottleneck No. 3

 

The system must be devoid of large planets with elliptical orbits (of the sort recently discovered), which would eject or destroy smaller planets.

 

Bottleneck No. 4

 

On the other hand, large planets with circular orbits are needed--at the right distance--to sweep the way clear from those pesky killer astroids (or comets) that would otherwise strike inner planets with regularity, cuasing mass extinctions every 100 thousand years instead of every 100 million

 

Bottleneck No. 5

 

To be habitable, a planet must not only maintain a circuluar orbit within the "Goldilocks zone", but must take the right-sized orbit within this zone. According to NASA astronomer Michael Hart's computer simulations: "If the Earth's orbit were only 5% smaller than it actually is, during the Early stages of Earth's history there would have been a 'runaway greenhouse effect', and the temperatures would have gone up untli the oceans boiled away entirely" On the other hand, he found that "if the Earth-sun distance were as little as 1% larger, there would have been runaway glaciation on Earth about 2 billion years ago. The Earth's oceans would have frozen over entirely and would have remained so ever since, with a mean global temperature of less than -50'F" Similar conclusions were reached by two other astronomers using different computer models.

 

Bottleneck No. 6

 

A habitable planet must be large enough to hold an atmosphere and small enough so that its gravity doesn't cursh everything on its surface. Also, it must be the right size in order to hold onto the right kind of atmosphere: too small and it won't hold water vapor; too large and it will hold onto hydrogen, methand, and ammonia, like Jupiter. A third requirement, moderate temperature, is also dependant upon planet size. Astronomers calculate that unless a planet has a mass at least .85 of Earth's mass, but no larger than 1.33 of Earth's mass, temperature variations would make the planet unihabitable within 2 billion years.

 

 

There are about 6 more bottlenecks listed, but I'm tired of typing right now. What do you guys think about these? The problem I see with all of these is that they are assuming life would develop like life on earth. This is another important issue: how many ways could life develop? Would life work in any other arrangement?

[Sayonara]

This still leaves massive scope for intelligent species though.

 

Yay.

[fafalone]

If 0.0000000001% of stars have suitable planets orbitting them, that's still ALOT of planets.

[Glider]

Absolutely. Numbers like that still present a high probabilty for intelligence.

[DocBill]

Originally posted by Glider

Absolutely. Numbers like that still present a high probabilty for intelligence.

 

Actually, if we limit ourselves to the idea of a carbon backboned chain of molecules as "life." This still leave many possibilities. BUT..there are many other possibilities (for exdample Silicon based). Only anthropic idoelogy insists life must resemble Earths.

 

Bill

[spuriousmonkey]

and the jury is still out on if there is actually intelligent life on this planet...

[DocBill]

Originally posted by spuriousmonkey

and the jury is still out on if there is actually intelligent life on this planet...

 

That's not very nice...think of the Dolphins!

 

Bill

[Glider]

Originally posted by DocBill

Actually, if we limit ourselves to the idea of a carbon backboned chain of molecules as "life." This still leave many possibilities. BUT..there are many other possibilities (for exdample Silicon based). Only anthropic idoelogy insists life must resemble Earths.

 

Bill

Absolutely true. However, the term 'intelligence' makes no such assumption.

 

Originally posted by spuriousmonkey

and the jury is still out on if there is actually intelligent life on this planet...

Hehehe...Position in the food chain apparently isn't a good indicator either. I used to have rats which showed a startlingly high degree of intelligence, they used to surprise me constantly with their ingenuity (especially where food was involved). However, I now have a cat who apparently can't tell the difference between a mouse and a volvo. He's spent the last 6 weeks recovering from a fractured pelvis.