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<div class="moz-cite-prefix">Generally, astrobiologists and
planetologists are getting more optimistic about habitability of
this kind of world:<br>
<a class="moz-txt-link-freetext" href="http://arxiv.org/pdf/1012.1883.pdf">http://arxiv.org/pdf/1012.1883.pdf</a><br>
<a class="moz-txt-link-freetext" href="http://arxiv.org/ftp/arxiv/papers/1510/1510.03484.pdf">http://arxiv.org/ftp/arxiv/papers/1510/1510.03484.pdf</a><br>
<br>
Tidally locked waterworlds have fairly moderate temperatures:<br>
<a class="moz-txt-link-freetext" href="http://arxiv.org/abs/1001.5117">http://arxiv.org/abs/1001.5117</a><br>
and can avoid dessication:<br>
<a class="moz-txt-link-freetext" href="http://arxiv.org/pdf/1411.0540.pdf">http://arxiv.org/pdf/1411.0540.pdf</a><br>
<br>
Also, just because it is tidally locked does not mean it has no
days:<br>
<a class="moz-txt-link-freetext" href="http://arxiv.org/pdf/1006.2503.pdf">http://arxiv.org/pdf/1006.2503.pdf</a><br>
<br>
On 2016-02-01 19:11, spike wrote:<br>
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<p class="MsoNormal"><span
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<p class="MsoNormal"><b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">From:</span></b><span
style="font-size:11.0pt;font-family:"Calibri",sans-serif">
extropy-chat [<a class="moz-txt-link-freetext" href="mailto:extropy-chat-bounces@lists.extropy.org">mailto:extropy-chat-bounces@lists.extropy.org</a>]
<b>On Behalf Of </b>John Clark<br>
<b>Sent:</b> Monday, February 01, 2016 9:03 AM<br>
<b>To:</b> ExI chat list
<a class="moz-txt-link-rfc2396E" href="mailto:extropy-chat@lists.extropy.org"><extropy-chat@lists.extropy.org></a><br>
<b>Subject:</b> Re: [ExI] Gaian Bottleneck<o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">On Mon,
Feb 1, 2016 at 9:26 AM, spike <<a
moz-do-not-send="true" href="mailto:spike66@att.net"
target="_blank"><a class="moz-txt-link-abbreviated" href="mailto:spike66@att.net">spike66@att.net</a></a>> wrote:<o:p></o:p></span></p>
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<p class="MsoNormal"><span
style="font-size:13.5pt;font-family:"Arial",sans-serif;color:#1F497D">>…</span><span
style="font-size:13.5pt;font-family:"Arial",sans-serif">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<span style="color:#1F497D">…</span></span><o:p></o:p></p>
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> <o:p></o:p></span></p>
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<p class="MsoNormal">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.<o:p></o:p></p>
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<p class="MsoNormal"><o:p> </o:p></p>
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<p class="MsoNormal"><span
style="font-size:13.5pt;font-family:"Arial",sans-serif"><span
style="color:#1F497D">>…</span>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<span
style="color:#1F497D">…<o:p></o:p></span></span></p>
<p class="MsoNormal"><span
style="font-size:13.5pt;font-family:"Arial",sans-serif;color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">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. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">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. <o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">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.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">OK
John, I think you are right: that would be a
terrible place to evolve. The beasts would just
stay in the sea.<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif"><o:p> </o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">spike
<o:p></o:p></span></p>
<p class="MsoNormal"><span
style="font-family:"Arial",sans-serif">
<o:p></o:p></span></p>
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<p class="MsoNormal"> <span style="font-size:11.0pt">…<o:p></o:p></span></p>
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<p class="MsoNormal"><span style="font-size:11.0pt"><o:p> </o:p></span></p>
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<pre class="moz-signature" cols="72">--
Dr Anders Sandberg
Future of Humanity Institute
Oxford Martin School
Oxford University
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