# If the Moon had gravity as strong as the Earth's, and a magnetic field, could it have supported life?

If the Moon had gravity as strong as Earth's, and a magnetic field, could it have supported life? Because if the Moon had as much gravity as Earth, it could have retained more water than is present today on the surface.

If the Earth is in the habitable zone, does the Moon also lie in the habitable zone?

• I think plate tectonics are also considered to be quite vital for life, as this process replenishes the nutrition for primitive life on the surface of a planet. Jan 12, 2013 at 13:32
• Sounds like a good candidate for the XKCD what if? section.
– l0b0
Jan 12, 2013 at 18:02
• as good as ???? Dec 1, 2015 at 0:15

However, habitability is not the same as being in the habitable zone, and the detailed answer depends on how you make the surface gravity match that of Earth. The surface gravity of a sphere of radius $R$ and average density $\rho$ is $$g = \frac{4\pi}{3} G \rho R.$$ Most rocky bodies in the Solar system have about the same density - that of a rock - so making the Moon's gravity match the Earth's is just a matter of making it bigger. Essentially it would become Earth's twin in every way.