I am trying to make a planet for my story that is slightly larger than earth. Planet has similar characteristics to earth, meaning it supports an environment similar to earth and is in the habitable zone. Its star system contains a single star. Other than the size it is almost earth-like. 1.2 refers to the surface area of the planet

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    $\begingroup$ Do you want it to be the same density (which means higher gravity), or lesser density (with the same gravity)? $\endgroup$ – Alexander Jun 7 '18 at 18:36
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    $\begingroup$ Preferably with the same gravity as earth if possible $\endgroup$ – Harbinger Jun 7 '18 at 18:37
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    $\begingroup$ It's probably going to be pretty Earth-like in that case, but it would be far better if you can specify what characteristics you're interested in. It seems to me you've fixed the size, gravity, environment, atmosphere and a whole bunch of other things, so I'm not sure what exactly you want us to tell you. Please Edit your question to specify your specific concern. $\endgroup$ – a CVn Jun 7 '18 at 19:02

A sphere has a surface area of 4*PI*radius^2. For Earth's radius of 6371 km, that gives us 5.1*10^8 km^2 of surface area.

Your planet has a surface area of 6.12*10^8 km^2 and a radius of 6977 km.

It has a volume 1.31 times larger than earth.

If the gravitational acceleration stays the same, that means the mass increases by a factor of 1.2 as well because AccGravitational = G*MassPlanet/(PlanetRadius^2).

So the density has decreased by a factor of 1.2/1.31, or ~91% of Earth's density.

This could be accomplished by having a smaller core, but that could slightly weaken the magnetic field. That could yield greater rates atmospheric loss to solar wind and more UV exposure.

If it has the same 24 hour day, then the outer edge will be rotating 9.5% faster. That could cause some faster high altitude winds, which would impact weather patterns in a potentially chaotic way.

If the same volume of air is present, it will now be spread out over more land and atmospheric pressure will decrease.

You could keep the 365 day orbit without having to change anything.

So those are the major changes that will occur from a physics perspective. The rest is up to you, as you could tweak any little variable to produce your desired outcome.

A less dense planet could have a more flimsy crust, and therefore more tectonic activity. The faster rotation could cause chaotic weather patterns.

Depending on the land / sea ratio, you would have different global weather patterns as well.

Since our sample size of Earth like planets is presently one, feel free to make your planet how you want and don't worry too much about the explanations.

  • $\begingroup$ Try calculating the density with an Earth-sized core and extra mantle to make up the difference in radius. $\endgroup$ – Spencer Jun 8 '18 at 2:37

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