# How significant is a planet's density to the formation of life?

I'm doing some writing set on a fictional earthlike planet that for reasons needs to be substantially larger than Earth but can't have substantially higher gravity. I've been able to compromise with a planet that's 6x the circumference, having a surface gravity of 1.5G, yielding a density of about 4700kg/m^3.

This is quite a bit (~15%) less than Earth and Venus, but (20%) more than Mars. It would proportionally have less heavy metal, meaning less iron for a protective magnetic field. I would like this planet to have some basis in reality - could such a planet be earth-like, and is there a definitive range of planet densities where life as we know it could exist?

• Prominent planetary scientist David Stevenson explains that too high content of metal also destroys the magnetic field, because high conductivity cools the core faster. It is temperature differences that matter to allow for convection, which moves matter that create the magnetic field of a planet. Jul 18, 2015 at 5:02
• Right now, anything people say about life elsewhere is extrapolating from a sample size of one. Extrapolating from a sample size of one is a spectacualy bad idea. Jul 18, 2015 at 6:47
• @DavidHammen That's a view based on great simplification. Our ancestors murdered all other great ape races, so our intelligence might not have arisen only once. Stone tools were used 3.3 million years ago, before even Homo Erectus appeared. And all life on Earth is family now, maybe not because life on Earth arose once, but because we ate all the other lifeforms. Biology is immensely rich and it is possible to extrapolate from it. Earth' biosphere is not a single point of data. Jul 18, 2015 at 7:18
• What is "life as we know it?". There are obviously gravity limits for a giraffe! I also can't reproduce your calculation. I get 5g. Jul 18, 2015 at 10:07
• My bad, I meant to say circumference. With a radius of 71000km and a g of 15m/s, ρ = 4754 kg/m^3 Jul 20, 2015 at 16:04