On Fri, Jan 18, 2019 at 09:29:17AM +0000, Phil Pugliese (via tml list) wrote:
> Wouldn't surface gravity be a problem on a 'Super-Earth'?
> Could/would it be possible to have 1G at the surface of a planet 5X
> the mass of Terra?

Yes, if the density was lower.  For example, Gliese 1214b appears to
have a mass of more than 5x that of Earth, but the visual radius is
also more than 2.5x.  That would give it a surface gravity probably
less than Earth's.  However, we don't know which of many possibilities
for its composition might be true.

It might be a water world, with surface gravity similar to its
estimated value at top of atmosphere.  Though in this particular case,
a better name would be steamworld due to its distance from the star.
Oceans can exist at 150 C, given a somewhat denser atmosphere.
Other waterworlds might be more hospitable.

However, it might instead be a smaller rocky world with a thick
atmosphere of hydrogen. In that case the gravity at the surface
underneath all the gas might be somewhat greater than at the top of
atmosphere, and the pressure greater than the Challenger Deep.

A third possibility would be a mini gas giant with no well-defined
transition between gas and liquid, so that "surface" gravity doesn't
apply and there wouldn't be a surface to build a habitat on anyway.

- Tim