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Name: Gary Flatow
Status: other
Age: 40s
Location: N/A
Country: N/A
Date: 2000-2001

I'm a docent at the California Academy of Sciences and lead school groups and adults on tours focused on Earth and space sciences. During a tour, I mentioned that Jupiter and Saturn had no solid surface, and then later, I mentioned how the surface gravity of Saturn was only slighly more than Earth, even though it's so much larger. Someone asked, "how do you have surface gravity when there is no surface?" And of course, I had no idea. What is the "surface" that astronomers refer to when they measure "surface gravity" on Saturn? And if they picked some other point as the surface, would the force of gravity be different?

The surface gravity is for the point on the planet where the optical density is 1.0. Since there is no real surface, this is what is used as the effective radius for such measurements.

Nathan A. Unterman

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