Jupiter and Saturn Surface
Date: 1999 - 2000
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?
Where is the surface of a cloud? Even though you know that a cloud is just
a misty fog, from a distance it appears to have well-defined edges. The gas
giant planets are the same. Although it's technically impossible to point
to a precise place where the "surface" is, you can get pretty close.
Richard E. Barrans Jr., Ph.D.
PG Research Foundation, Darien, Illinois
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Update: June 2012