[ExI] Gaian Bottleneck

spike spike66 at att.net
Mon Feb 1 19:11:44 UTC 2016



From: extropy-chat [mailto:extropy-chat-bounces at lists.extropy.org] On Behalf Of John Clark
Sent: Monday, February 01, 2016 9:03 AM
To: ExI chat list <extropy-chat at lists.extropy.org>
Subject: Re: [ExI] Gaian Bottleneck


On Mon, Feb 1, 2016 at 9:26 AM, spike <spike66 at att.net <mailto:spike66 at att.net> > wrote:


>…A planet that close would be gravitationally locked with one side in perpetual day and the other in perpetual night; that might not be an impossible burden for life but it certainly wouldn't help…


​> ​

Ja.  Tide locked planets would have one small advantage for emerging lifeforms however: there would be a twilight ring at the transition between the day side and the night side.  It would be a very limited strip of real estate, but it would have mild temperatures there always and perhaps liquid water, along with perpetual direct sunlight right down on the horizon.


​>…But the twilight zone would also be subjected to ferocious winds that never relent as the hot and cold halfs of the planet try, unsuccessfully, to equalize their temperature; and that would probably prevent the evolution of large plants or animals…



Ja, there is that.  Could be the atmosphere on such a world would be sufficiently tenuous that a strong wind might not amount to much.  Force in a compressible flow varies as the square of the velocity, so we can imagine a steady cold wind of 100 m/sec at 0.1 atmosphere being a force equivalent to 30 m/sec wind here.  That would be a breezy day for sure, but nothing that would stop existing lifeforms here.  Constant sixty mile an hour winds happen here in places.  Very unpleasant, but stuff lives.  


Down near the surface the wind patterns would be slower and more chaotic.  Life could evolve under the sea, then make their way up on a harsh blustery landscape.  Liquid water can exist at 0.1 atm.  We can take it further: liquid water can exist at 0.01 atm, so a 100 m/sec of that would be equivalent to a light breeze one would scarcely notice.  


As I wrote this, it occurred to me that such a planet would be at nearly 100% humidity everywhere.  Think about it: wind blows from the cool side, hits the twilight zone, starts to warm picks up moisture from any existing seas, density decreases as it goes sunward, air rises, circulates back crossing into darkness again at high altitude, drops the moisture which falls as rain.  That twilight zone would suffer from not only constant cold wind from the dark side, but from a continuous hurricane-force rainstorm, or perhaps blizzard.  Even if the atmosphere is a tenuous .01 atm, it would accelerate and drive that ice and rain like little bullets.


OK John, I think you are right: that would be a terrible place to evolve.  The beasts would just stay in the sea.






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