Large Habitable worlds

[Hunter Parasite]

Can there be a world that is 5 times the size and mass of earth, that has life like trees, or ferns, or grass, or even algae? How about something a bit bigger? Maybe a small lizard, better yet, why not a humanoid or similar being? Would they have to grow larger in order to take the gravitational pull? Could a large planet form from a relativly weak gravatational field, like ours?

[eburacum45]

I work out that a planet with the same density as Earth but five times the mass will have a radius of roughly 11000 km and a surface gravity of roughly 1.7 gee. The Earth has a radius of about 6400km for comparison.

Such a planet would have a much denser atmosphere than Earth's, in all probability, so it will be uncomfortable or actually impossible for unmdified humans to live there. Land animals will weigh nearly twice as much, so are likely to have many, strong legs. Bipeds are unlikely but not impossible; a biped would need to have massvely strong lower limbs to carry the weight of such a creature. Imagine carrying a person 0.7xyour own weight on your back all day.

I suspect that most creatures will be small and low-slung, with strong limbs or perhaps many multiple limbs. Very large creatures are unlikely, in my opinion, but creatures will probably be stronger in the limbs than Earth species.

[ZZ-Cephei]

You gave me the idea ...

[ajtribick]

Against 5 Earth-mass habitable planets, this paper suggests that the planet could start gas accretion possibly as low as ~2 Earth-masses and end up as a gas giant.

[Neethis]

Against 5 Earth-mass habitable planets, this paper suggests that the planet could start gas accretion possibly as low as ~2 Earth-masses and end up as a gas giant.

How about if it formed close to its parent star, and then migrated outwards, after the majority of the nebula gas had been blown away or consumed by other planets?

[Malenfant]

Against 5 Earth-mass habitable planets, this paper suggests that the planet could start gas accretion possibly as low as ~2 Earth-masses and end up as a gas giant.

How about if it formed close to its parent star, and then migrated outwards, after the majority of the nebula gas had been blown away or consumed by other planets?

Planets usually migrate inwards (due to drag in the nebula), not outwards. Tidal forces wouldn't be enough to push the planet out significantly.

[Neethis]

Against 5 Earth-mass habitable planets, this paper suggests that the planet could start gas accretion possibly as low as ~2 Earth-masses and end up as a gas giant.

How about if it formed close to its parent star, and then migrated outwards, after the majority of the nebula gas had been blown away or consumed by other planets?

Planets usually migrate inwards (due to drag in the nebula), not outwards. Tidal forces wouldn't be enough to push the planet out significantly.

Ah ok, nevermind than