08-12-2022, 08:43 AM | #11 | |
Join Date: Jun 2006
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Re: Number of habitable worlds within170 light years?
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Breathable air only exists because of rather complicated biological processes, and we really have no good constraints even on how many worlds have life, let alone life that happens to have exactly this or a sufficiently similar biochemistry to dump something as weird as free oxygen into the air.
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08-12-2022, 11:02 AM | #12 |
Join Date: Aug 2014
Location: Canada
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Re: Number of habitable worlds within170 light years?
You guessed exactly right! Lol
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Oliver. |
08-12-2022, 11:04 AM | #13 | |
Join Date: Aug 2014
Location: Canada
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Re: Number of habitable worlds within170 light years?
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Oliver. |
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08-12-2022, 11:06 AM | #14 | |
Join Date: Aug 2014
Location: Canada
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Re: Number of habitable worlds within170 light years?
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Oliver. |
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08-12-2022, 11:42 AM | #15 |
Join Date: Dec 2007
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Re: Number of habitable worlds within170 light years?
More than a thousand if you set the bar low and just settle for liquid water. Actual breathable air without many centuries of terraforming? I suspect the number would be more like a hundred.
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08-12-2022, 12:05 PM | #16 |
Hero of Democracy
Join Date: Mar 2012
Location: far from the ocean
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Re: Number of habitable worlds within170 light years?
So life shows up on earth pretty quickly, which gives hope for finding life most times you get what space calls an "Ocean world". I don't think that the oxygen energy storage loop is particularly unlikely: oxygen is the third or fourth most common element in the universe, and its energy storage properties are amazing. It did take 2 billion years (roughly) to show up on earth though, and that could be slow, or it could fast. Sample sizes of one are tricky. The roughly breathable atmosphere of earth seems to show up at the same time as multicellular life, or conversely that multicellular life shows up once all of the oxygen sinks on earth are used up and the oxygen level spikes.
So there is a fair argument that "water planets" are slow pressure cookers that eventually give multicellular life. That is in fact what we would assume, if not for Fermi and his blasted paradox. Which makes everyone go back and furiously try to make the numbers lower.
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08-12-2022, 12:32 PM | #17 | |
Join Date: Feb 2005
Location: Berkeley, CA
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Re: Number of habitable worlds within170 light years?
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08-12-2022, 01:33 PM | #18 | |
Join Date: Apr 2005
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Re: Number of habitable worlds within170 light years?
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While the Moon doesn't do that much to protect the Earth from asteroids, it might play a big role in helping to maintain the Earth's magnetic field, by keeping the earth's core molten, which is critical in preventing deadly cosmic rays from reaching the planet. From a biological point of view, tides and seasons aren't quite as important, but their constant action might serve to literally stir the pot by moving water (hence nutrients) around. Vulcanism also plays a role by constantly bringing denser elements to the planet's surface. If planets with molten rock/metal cores and extensive vulcanism are rare, that means that planets with habitable surfaces are rare (due to constant bombardment by cosmic rays), limiting life, and sapient life, to just planetary oceans. Decades of wishful thinking to the contrary, while ocean-dwelling life might develop sapience it's unlikely to develop extensive tool use. (Consider that there species of cetaceans and octopi which are very smart, and sometimes demonstrate tool-using behaviors, but haven't shown much inclination towards tool making.) If the surface of most planets is hostile to terrestrial life, aquatic species would have no inclination to spend much time on land, much less evolve to live there. Add three more layers to Drake's Equation and Fermi's Paradox might not be so paradoxical: "x chance that a planet has the right geophysical makeup to potentially block cosmic rays." "x chance of a lucky planetary collision which doesn't destroy the planet, but which does provide an Earth-like moon to "keep the pot boiling."" (Alternately, the presence of other gravitational forces which generate vulcanism.) "x chance that terrestrial life evolves." |
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08-12-2022, 04:47 PM | #19 | |
Join Date: Jun 2006
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Re: Number of habitable worlds within170 light years?
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Want a space opera like universe with a thousand shirtsleeve planets - life is common and the oxygen cycle is universal. Want a setting where there are thousands of planets where you could set up habitation domes with some effort but the two known oxygen worlds are prizes of immense value worth fighting over, life is rare but the oxygen cycle is normal. Want a setting where there are thousands of worlds with alien biospheres but none of the have breathable air and the dozen different alien species in campaign flee for their lives if the Terran's airsuits spring a leak and start spewing horrible war grade chemical weapons into the atmosphere. You can do that too.
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08-12-2022, 06:33 PM | #20 |
Join Date: May 2019
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Re: Number of habitable worlds within170 light years?
What Malloyd said. Also, my personal guess for the Fermi Paradox solution is that, even if all life-bearing worlds evolve intelligence, they're very unlikely to evolve it at the same time. Modern humans have been around for, what, 100,000 years, at most, and transmitting radio waves for 100; even if you round that way up to a 1 million year lifespan for our species (before we go extinct/transcend/whatever), that's 1/500th of the time since the Cambrian Explosion (ca. 500 mya). So figure a planet with macroscopic (i.e. big enough to see) multi-cellular life has a 1/500 or 0.2% chance of having intelligent life on it right now.
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