Why are Planets Round?
Asking on behalf of the class teacher who brought students
to the lab: "Why planets are spherical?
If one weren't, it would collapse to a sphere under its own gravity. All
the matter tries to fall toward the center, and will if there's nothing in
its way. The sphere is the shape in which everything has fallen toward the
center as far as it can.
Actually, planets bulge out a little at their equators, because of their
rotation. So they're not exactly spherical, but pretty close.
Richard E. Barrans Jr., Ph.D
PG Research Foundation, Darien, Illinois
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Update: June 2012