Will my planet work? (size, gravity, atmosphere)

Question

I was going to sort this all out beforehand, and then write the book, but when the writing flows... you make hay. I am a perfectionist/details-oriented person, but you lose me on math/hard science. The book is written, so now I will ask, figure this out, and hopefully not have to take a chainsaw to the thing to change what I got wrong. I do not think I am TOO far off based on a LOT of lurking here, on google and wiki...

I have a world, and I have decided I want a bigger planet than Earth, as big as possible really, without being too much different in some important ways. I wanted bigger continents, bigger oceans/seas, taller mountains, larger/taller flora, and I wanted a slightly cooler climate (for a bit more boreal and a bit less jungle). I also wanted potentially bigger creatures. Basically? more extremes. Yeah, it's an epic fantasy in a made up world and I should just write my dragons and polish my swords, but I want to please the nitpickers too. Further, this epic (medieval) fantasy has potential to go sci-fi down the road, and then I will definitely have to please the nitpickers.

So... from my research so far... this should look like a planet roughly 1.15 to 1.2 times the size of Earth (diameter), to the extreme (outer) edge of the habitable zone (this is important, more on this in a different post), with a thicker atmosphere (and more oxygen), but slightly less gravity than Earth. I figured that having less gravity vs a larger planet can be solved by having a slightly lighter core, consisting of less iron perhaps. It will have roughly the same land/water ratio as Earth.

If it helps/hinders the post, i'll also mention that the planet has a VERY large moon (again, big as possible), OR... it might even be the satellite of a gas giant, maybe even a brown dwarf? I'm not picky on this one, i just want the big moon. It also has another moon, same as our own, and then a smaller third.

So... actual question:

Will my planet template work? Scientifically plausible? Almost plausible?

First time here and great site.

Thanks.

Answer 1

Your planet does not need to be bigger than Earth to have bigger stuff. Bigger geographic features would be consistent with a more volcanically active planet, not a bigger one. That means more heavy/radioactive metals like Uranium to keep the core hotter than the crust can contain.

That also makes your world more dense meaning you'd need a smaller than earth world to get the gravity low enough to support bigger organisms.

A larger than Earth planet could potentially have the lower density to support large life forms or the volcanic activity to support large mountains, but probably not both.

As for the Moon-Planet relationship, it is believed that the tidal forces generated by a moon are necessary for the formation of life. Multiple moons should not prevent life from forming and evolving, but it may make certain environmental cycles less predictable creating a more hostile environment than we are used to. When the moons space out just wrong, they will neutralize each other's pull inhibiting oceanic currents causing the poles to become colder and the equator to heat up to excruciating levels. Inversely, when their orbits line up to much the tides would become so powerful that coastline would be pummeled by a continuous barrage of tsunami sized waves, and that extra hot equatorial weather will meet the extra cool polar weather causing massive storms.