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← Newest alien planet is just the right temperature for life

mmurray's Avatar Jump to comment 16 by mmurray

Comment 14 by SnowyDoc :

@ rjohn19

The force of gravity acting at the surface depends on the mass of the planet, which we don't yet know. If we assume (and it's a big assumption) that the density is the same as that of the Earth, then it would have roughly 14 times the mass of the Earth, and the gravity felt at the surface would therefore be roughly 14 times that on Earth.

So yes, it would be a tad uncomfortable. :-)

I'm not sure this is the right calculation. As the planet gets bigger people on the surface are further away from the centre.

I think the correct calculation goes as follows. The gravitational force on a person of mass m on the surface of a planet of mass M is the same as if you make the planet into a point mass as its centre. As the person is relatively small compared to the planet you can make them a point mass as well. If the density of the planet is d and assumed constant and radius is r then the mass of the planet is

M = d [ (4/3) pi (r cubed) ]

the force is

F = C (m M ) / ( r squared)

where C is some constant. So ignoring all the constants the force is proportional to the radius. Hence gravity should be 2.4 g on the surface of this planet of gravity if g on the surface of earth.. Uncomfortable for us but evolution could have adapted I think.


EDIT: See also wikipedia.

Wed, 07 Dec 2011 04:43:10 UTC | #896365