[ExI] Gaian Bottleneck

[Anders Sandberg]

Generally, astrobiologists and planetologists are getting more 
optimistic about habitability of this kind of world:
http://arxiv.org/pdf/1012.1883.pdf
http://arxiv.org/ftp/arxiv/papers/1510/1510.03484.pdf

Tidally locked waterworlds have fairly moderate temperatures:
http://arxiv.org/abs/1001.5117
and can avoid dessication:
http://arxiv.org/pdf/1411.0540.pdf

Also, just because it is tidally locked does not mean it has no days:
http://arxiv.org/pdf/1006.2503.pdf

On 2016-02-01 19:11, spike wrote:
>
> *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.
>
> spike
>
> ​
>
> …
>
>
>
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-- 
Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University

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