New answers tagged planetary-science
26
Yes, it is possible. As James K observed in a comment, the surface gravity of Uranus is slightly less than that of Earth, but its mass is 14 times larger. If Earth were orbiting Uranus, it would be a very large moon, but it would still be considered a moon, and thus a moon with a higher surface gravity than its planet.
The reason this is possible is that ...
34
Yes, it is.
Given two spherical, uniform, bodies one with mass $m_1$ and radius $r_1$ and the other with mass $m_2$ and radius $r_2$, then the surface acceleration due to gravity will be equal when
$$r_2 = \sqrt{\frac{m_2}{m_1}} r_1$$
For the Moon to have the same surface gravity as the Earth, we can plug in suitable numbers, and you end up with a radius ...
92
Given a pair of objects that are gravitationally bound to each other, they will orbit around their common barycenter (center of mass of the system). The object to be most logically deemed the moon will be the one of lesser mass because it will be further from the barycenter than its companion.
For example, Pluto has a gravitationally bound companion named ...
72
Gravity isn't just about mass, but about distance, too.
Our moon has a surface gravity of about 1/6th of Earth, because it is small and less dense than the Earth is. Surface gravity of a body is inversely proportional to the square of its radius, holding mass constant. That means that if you compressed the moon such that it was $\frac{1}{\sqrt{6}}$th of its ...
2
What I should have been looking at is the Geoid of Mars & the depth from it to the mantle
The thickness of the crust varies between 50 km & 22 km due to the Geography & features (rock layers) above the Geoid while the distance from it to the mantle should be reasonably uniform.
I presume the putative Geoid of Mars is the altitude used for ...
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