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Swift
2015-Jan-26, 06:17 PM
The January 2015 issue of Scientific American has an article "Planets More Habitable Than Earth May Be Common in Our Galaxy" (preview link (http://www.scientificamerican.com/article/planets-more-habitable-than-earth-may-be-common-in-our-galaxy/) - rest behind paywall)


Do we inhabit the best of all possible worlds? German mathematician Gottfried Leibniz thought so, writing in 1710 that our planet, warts and all, must be the most optimal one imaginable. Leibniz's idea was roundly scorned as unscientific wishful thinking, most notably by French author Voltaire in his magnum opus, Candide. Yet Leibniz might find sympathy from at least one group of scientists—the astronomers who have for decades treated Earth as a golden standard as they search for worlds beyond our own solar system.

Because earthlings still know of just one living world—our own—it makes some sense to use Earth as a template in the search for life elsewhere, such as in the most Earth-like regions of Mars or Jupiter's watery moon Europa. Now, however, discoveries of potentially habitable planets orbiting stars other than our sun—exoplanets, that is—are challenging that geocentric approach.

The idea is that Earth, particularly current Earth, is not the ultimate in habitablity, and we shouldn't just look for Earth-twins, but planets even better than Earth for supporting life.

The author's idea for such planets are the super-Earths, maybe 2x or 3x bigger than Earth, and closer to a slightly smaller star than our sun. Such a star would have a longer period of time that it remains stable, and such a super-Earth might have a thicker atmosphere and a flatter topography, leading to a "archipelago world" of shallow seas and numberous islands and small continents.

Noclevername
2015-Jan-26, 07:54 PM
If we could build the generation ships needed to send humans to those planets, we wouldn't really need those planets. We'd already have the capacity to live for generations without planets.

eburacum45
2015-Jan-27, 06:22 AM
Planets much bigger than Earth would also have significantly stronger gravity - this could change the environment radically, and would make the planet uncomfortable for unmodified humans. Do we want to have large populations of radically altered humans in the Galaxy?

(Personally I would be fine with this).

Swift
2015-Jan-27, 01:43 PM
Just so it is clear... my thread title of "Maybe we could do better" was entirely meant as a joke. I was making no implication that humans would be visiting or colonizing any such planets, if such planets exist. The authors of the article didn't even hint about such a thing in the article.

The entire point of both the article and my thread about it was that in our search for life elsewhere in the Universe, "Earth-like" planets may not be the best choice to investigate, but these "more habitable than Earth" planets may be.

To eburacum45's point about gravity, the author's included the higher gravity in the factors that would make it more habitable. A bigger world with more gravity would tend to have a thicker atmosphere, a larger, more active core, leading to more several effects they contend are more desireable (more volcanoes, more gases from those volcanoes, more plate tectonics and recycling of carbon and other materials, stronger magnetic field for protection, longer period of time core is still molten), and the flatter topography I mentioned in the OP.

Noclevername
2015-Jan-27, 01:50 PM
"Earth-like" planets may not be the best choice to investigate, but these "more habitable than Earth" planets may be.

My tuppence? Life adapts. Any planet with life is habitable by definition, and it may be that a planet too amenable to life will lack the evolutionary challenges that lead to complex life. They might have it too easy to need to change or diversify much.

profloater
2015-Jan-27, 02:47 PM
We will probably design AI and send that off to explore so the ideal planet may be rather different! Why assume we are the end point of evolution? just joking of course, we know humans are perfect, :p

iquestor
2015-Jan-27, 06:31 PM
Just so it is clear... my thread title of "Maybe we could do better" was entirely meant as a joke. I was making no implication that humans would be visiting or colonizing any such planets, if such planets exist. The authors of the article didn't even hint about such a thing in the article.

The entire point of both the article and my thread about it was that in our search for life elsewhere in the Universe, "Earth-like" planets may not be the best choice to investigate, but these "more habitable than Earth" planets may be.

To eburacum45's point about gravity, the author's included the higher gravity in the factors that would make it more habitable. A bigger world with more gravity would tend to have a thicker atmosphere, a larger, more active core, leading to more several effects they contend are more desireable (more volcanoes, more gases from those volcanoes, more plate tectonics and recycling of carbon and other materials, stronger magnetic field for protection, longer period of time core is still molten), and the flatter topography I mentioned in the OP.

I would think any "super-habitable" worlds would easily show up in our current searches for earth-like worlds. They are still in goldilocks zones, rocky, and around the same size. We would be looking for the same signatures in their atmospheres. I doubt there are any characteristics they might have that we wouldn't be on the lookout for.

Swift
2015-Jan-27, 06:42 PM
I would think any "super-habitable" worlds would easily show up in our current searches for earth-like worlds. They are still in goldilocks zones, rocky, and around the same size. We would be looking for the same signatures in their atmospheres. I doubt there are any characteristics they might have that we wouldn't be on the lookout for.
I don't know about the "easily" part, but the authors point out that several worlds fitting this criteria have already been found. I think the point they were mostly addressing is exactly the work you are talking about, looking for characteristic signatures in their atmospheres. I think that is currently beyond our technology, but is something we will achieve in the near future. I think their point regards how you prioritize the planets you examine.

iquestor
2015-Jan-27, 07:33 PM
I don't know about the "easily" part, but the authors point out that several worlds fitting this criteria have already been found. I think the point they were mostly addressing is exactly the work you are talking about, looking for characteristic signatures in their atmospheres. I think that is currently beyond our technology, but is something we will achieve in the near future. I think their point regards how you prioritize the planets you examine.

that makes sense. I do think we are close to the technology; some experts think we will have compelling evidence of exobiology in 5-10 years. No ground breaking discoveries have to be made. We have shown we can remotely characterize an exo-planet's atmosphere if the right conditions and alignments persist. We just have to refine the technology sufficiently to align optimally, and identify the elements we are looking for (CHON, Methane, photosynthetic signatures).

Noclevername
2015-Jan-28, 07:50 AM
Abiotic CHON is found in meteorites and some nebulae, even as complex molecules. So by itself it can't really be considered as evidence of life. Maybe in conjunction with some of the other signs, it might be supporting evidence.

Ross 54
2015-Jan-29, 05:48 PM
Oxygen plus traces of methane, found in exoplanet atmospheres, has been cited as a combination indicative of life.

Noclevername
2015-Jan-29, 05:50 PM
Oxygen plus traces of methane, found in exoplanet atmospheres, has been cited as a combination indicative of life.

Yes, that's what I was trying to say by "in conjunction with some of the other signs".

marsbug
2015-Jan-29, 09:14 PM
Just so it is clear... my thread title of "Maybe we could do better" was entirely meant as a joke. I was making no implication that humans would be visiting or colonizing any such planets, if such planets exist. The authors of the article didn't even hint about such a thing in the article.

The entire point of both the article and my thread about it was that in our search for life elsewhere in the Universe, "Earth-like" planets may not be the best choice to investigate, but these "more habitable than Earth" planets may be.

To eburacum45's point about gravity, the author's included the higher gravity in the factors that would make it more habitable. A bigger world with more gravity would tend to have a thicker atmosphere, a larger, more active core, leading to more several effects they contend are more desireable (more volcanoes, more gases from those volcanoes, more plate tectonics and recycling of carbon and other materials, stronger magnetic field for protection, longer period of time core is still molten), and the flatter topography I mentioned in the OP.

Higher gravity also means it would be harder for any sentient life there to get into space, a thicker atmosphere makes it harder for signals to get in and out, and more tectonic activity would make it harder for a civilisation to flourish -so WRT a humanlike intelligent civilisation (although something vastly different might arise and have no problems); it would be harder to get going and harder to explore beyond the homeworld. So more habitable for life generally might not mean better for us or creatures like us.

Swift
2015-Jan-29, 10:11 PM
Higher gravity also means it would be harder for any sentient life there to get into space, a thicker atmosphere makes it harder for signals to get in and out, and more tectonic activity would make it harder for a civilisation to flourish -so WRT a humanlike intelligent civilisation (although something vastly different might arise and have no problems); it would be harder to get going and harder to explore beyond the homeworld. So more habitable for life generally might not mean better for us or creatures like us.
Again, all of this could be true, but none of it was either my point or the article's authors'. They didn't even make a passing mention about intelligent life.

John Mendenhall
2015-Jan-30, 05:39 AM
An earthlike planet but a little bigger. If I recall correctly, Jack Vance's "big planet" SF novels.

marsbug
2015-Feb-01, 06:24 PM
Again, all of this could be true, but none of it was either my point or the article's authors'. They didn't even make a passing mention about intelligent life.

I wasn't meaning to put words into anyone's mouth, or detract from the original point, which is a very good one I think. I'm just trying to extend the discussion from where it started to (what seems to me to be) the next logical step

Ilya
2015-Feb-06, 09:37 PM
The article also points out that as a star ages, it grows brighter, and thus habitable zone moves outward. Earth is already almost on the inner edge of the Sun's HZ. 300 million years ago Sun was dimmer, and Earth's atmosphere had both more CO2 and more O2 -- and consequently more total biomass than at present. So not only Earth is not the most habitable planet: a planet's "habitability" can change with time, and habitability of Earth is on the decline.

Eclogite
2015-Feb-21, 05:44 PM
Again, all of this could be true, but none of it was either my point or the article's authors'. They didn't even make a passing mention about intelligent life.Unfortunately, all too often, mention alien life and all but the most disciplined seem to think of LGMs. For such people I think reading Ward and Brownlee's Rare Earth (http://books.google.co.uk/books/about/Rare_Earth.html?id=SZVV26vCSi8C&redir_esc=y) should be compulsory.

Ara Pacis
2015-Feb-22, 05:45 AM
a flatter topography might happen, but angle of repose is for lose regolith and rock formation might still stand tall against harsher gravity. But if the planet does have a flatter topography, the weather and climate may not be as varied as we have it. This may mean all storms would be tropical storms by genesis. However, a thicker atmosphere would apply to density, but not overall thickness (IIRC) because the scale height would be reduced. Not sure how all this would work out, but some interesting questions.

Barabino
2015-Feb-22, 12:21 PM
I argue that a flatter topography may be NOT as good as it sounds: Australia is much more dry than South America: uninhabitable high mountains like the Andes are good for making rain fall... :D

Noclevername
2015-Feb-22, 04:04 PM
I argue that a flatter topography may be NOT as good as it sounds: Australia is much more dry than South America: uninhabitable high mountains like the Andes are good for making rain fall... :D
Only on one side, see "rain shadow (http://en.wikipedia.org/wiki/Rain_shadow)".

marsbug
2015-Feb-23, 05:51 PM
Flatter topography relative to what? If the overall topography is lower but the clouds form at a level lower still (than on Earth) the topography is effectively higher! In terms of juist maximising biomass wouldn't a world with a warm deep global ocean be better? I can only get the preview for the article. I'd need to define what we mean by 'better' to answer the question in the OP. Better could, legitimately, mean 'most optimal for the development of intelligent life' (Little green space men with technology and language are considered the big BIG find by lots of people who work in astrobiology*, they just don't like to hope for it in their lifetime too much) or it could mean 'optimal for converting the most tonnage of organic material into functioning biology'. If the full article sets that could someone who's seen it tell me pretty please?

* I know one... so it's the big BIG thing for him and he says it is for others. I'm deciding to take that as evidence :D :D

Noclevername
2015-Feb-23, 06:17 PM
In terms of juist maximising biomass wouldn't a world with a warm deep global ocean be better?

I think that exposed landmass eroding in the wind and rain means more silt getting washed into the seas. Which means more organics and minerals available than on a total ocean planet with only slow deep sea currents to stir up the sea bottom.

Swift
2015-Feb-23, 06:48 PM
As Noclevername says, at least on Earth, the deep ocean is relatively devoid of life, except around things like hydrothermal vents. The species that do survive there, do so mostly on stuff coming down from above. The deep ocean is too deep for photosynthesis to be effective.

How much this might apply to other worlds.... I don't know.

marsbug
2015-Mar-02, 09:35 AM
By warm I meant, well warm all the way to the bottom - not sure how that would work in terms of geology. Lots and lots of black smokers? But I think that we might want to re-asses some basic assumptions of what a world of maximum habitability would look like: viable cryogenic/methanogenic protocell membrane modelled ? (http://www.news.cornell.edu/stories/2015/02/life-not-we-know-it-possible-saturns-moon-titan)