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What would be the specific conditions required for a planet to be a more ideal version of Earth?

I want the world to have a much larger proportion of land covered by lush jungle and forest ecosystems with only a very small fraction of the world populated by human-esque people.

It would be in a galaxy with a G star similar to our sun.

Would the conditions be almost identical to earth or are there any subtle or non-subtle improvements that could be made in any of earth's properties (atmosphere, geometry, etc.) that would provide a more suitable world for nature to thrive.

Cyn
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rendered_mercurius
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  • In this case you quickly received an answer that is very good but in general it is best to wait some time, perhaps a day, before accepting an answer as "The Answer." It is possible that there are other people who had not yet seen your question who could provide a more suitable answer, or perhaps a similar but more detailed answer. – krb Jul 24 '19 at 23:41

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In astrobiology, this concept is known as the 'Superhabitable Planet'.

Such a planet would be more massive than Earth, up to about 2.5 Earth masses. This additional mass provides shallower oceans, and lower topography. Additionally, it is likely that this feature will be paired with a thicker atmosphere, which distributes the warmth received from insolation more evenly from the equator to the poles.

The star that such a planet orbits would more suitably be a K-class orange dwarf. These stars emit much less UV radiation, and have longer lifespans. Additionally, the habitable zone around such a star doesn't move so much during the lifetime of the star, so over a long timescale, the planet's climate will be more stable.

Arkenstein XII
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  • Most astrobiologists consider Earth to be on the inside edge of the habitable zone, so I'm not sure a thicker atmosphere at Earth's orbital radius would be a good thing. At Mars' orbit though it'd probably be good. – stix Jul 24 '19 at 21:21
  • @stix for a dimmer K-class star, this orbit should be good. – Alexander Jul 24 '19 at 21:25
  • @stix Being more centred in the habitable zone would probably be nice. i.e a touch further out. – Arkenstein XII Jul 24 '19 at 21:43
  • True. It's also important to keep in mind the habitable zone changes over time. Astrobiologists are still trying to figure out how the Earth could have been in a habitable zone 4 billion years ago when life arose, given how much colder the Sun would have been, and in another few hundred million years, the Sun's output will be too hot for Earth. – stix Jul 24 '19 at 21:45
  • @stix One of the major benefits of a K-class star is that it doesn't get much hotter as it evolves. Certainly not so much as our sun has. – Arkenstein XII Jul 24 '19 at 21:46
  • Basically we're saying Earth isn't a particularly habitable planet and Sol isn't a particularly habitable star? :P

    And yet, it's the only place we know of where life works, but even then only on a single planet.

     – stix Jul 24 '19 at 21:50
  • @stix I've lived in two places on this planet of ours. The first, you could freeze to death for much of the year and the second the sun could burn your skin within hours. I don't think Earth is very habitable to be honest. – Muuski Jul 24 '19 at 21:59
  • @stix That's exactly the idea. Earth may be the most habitable planet in our solar system, but when compared to planets that should theoretically exist throughout the rest of the galaxy, Earth is really borderline. If this hypothesis is correct, it follows that life should be abundant elsewhere. – Arkenstein XII Jul 24 '19 at 22:10
  • @Arkenstein XII My answer to this question https://worldbuilding.stackexchange.com/questions/151298/whats-the-largest-an-earth-like-planet-can-be-and-support-earths-biosphere/151305#151305 includes a quote that claims a) plate tectonics are good for habitability and b) planets with mases more than about two times the mass of the Earth should be too massive for plate tectonics. So maybe you should either acknowledge that your planet is too massive, or else answer the other question with evidence that two times the mass of Earth is not the upper mass limit for a habitable planet. – M. A. Golding Jul 25 '19 at 17:50
  • @M.A.Golding My own reading suggests that the upper limit for plate tectonics exists at around 2.5 Earth-masses (assuming Earth-like composition) due to the formation of a thermally insulating transition zone at the base of the mantle. I'll have a read of the papers you linked in your answer. – Arkenstein XII Jul 25 '19 at 20:20
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    @M.A.Golding Having done some further reading on the topic, I can only conclude that this is very much an open topic in the field of Exoplanet science. Tackley et al. 2012 (Mantle Dynamics in Super-Earths) suggests that massive planets greater than 2 Earth-masses would in fact have highly convective deep mantles. – Arkenstein XII Jul 25 '19 at 23:44
  • In fairness, climate is affected by very much more than just solar radiation flux. – user Jul 26 '19 at 08:47
  • @aCVn That is true. The Superhabitable concept assumes a lot of things are simply earth-like. – Arkenstein XII Jul 27 '19 at 05:23