More thoughts on Terra-Uranus

Uranus apparently has a rocky core with a mass equivalent to 0.55 Earth's mass. Uranus's radius also equals about four times Earth's radius, and the core has a radius of about 0.2 of Uranus's radius, which therefore equals 0.8 times Earth's radius. This me gives a way to estimate the gravitational acceleration on the surface of the rocky planet inside Uranus, assuming that we could extract it without significant loss of its mass, and that it maintains its current radius. Until someone else comes up with a better name, I denote this new planet Terra-Uranus.

Gravitational acceleration on the surface of a planet varies directly as the planet's mass M, and inversely as the square of the planet's radius r. Earth has a gravitational acceleration on its surface at 9.8 m s^-2. Therefore gravitational acceleration on the surface of Terra-Uranus would approximately equal:

9.8 m s^-2 X 0.55 X (0.8)^-2 = 8.4 m s^-2

Compare this figure, 8.4 m s^-2, to Venus's surface gravity of 8.9 m s^-2. A planet with Terra-Uranus's level of surface gravitation could probably hold onto a substantial atmosphere over geologic time, like Venus and Earth.