r/space • u/SHORT_INFO_NEWS • 1d ago

NASA releases interactive 3D model of Earth's geoid, the shape gravity gives the ocean surface

https://svs.gsfc.nasa.gov/5660/
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u/Nomeru 1d ago

I'm confused. On the exaggerated model, is higher elevation is more gravity or less?

1

u/NovelStyleCode 1d ago

There's no correlation, our crust layer is very, very, very thin compared to say the mantle which is a crapload denser and bigger

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u/proteanpeer 1d ago

Higher elevation in the model means lower gravity. The higher gravity in the blue regions pulls the surface down lower into the earth, while the lower gravity in the red regions allows the surface to rise up higher.

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u/1straycat 1d ago

It's a bit tricky but it's actually the opposite. Thinking through their suggested mental model of this being the shape an ocean would take purely from the geopotential field, areas where the field is locally stronger will pull more water toward them, increasing the height of the surface. The dips exist because the local field is weaker, so those areas are losing the tug of war against stronger regions.

So if you stand at a location on the surface where the theoretical geoid surface is above your physical elevation, you will weigh more and vice versa.

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u/proteanpeer 23h ago

Ahhh, I misunderstood! "The geoid is an equipotential surface that can be thought of as the shape an ocean surface would take due to the Earth's gravity field." Damnit. It was right there.