Geophysical definition of planet

The International Union of Geological Sciences (IUGS) is the internationally recognized body charged with fostering agreement on nomenclature and classification across geoscientific disciplines. However, they have yet to create a formal definition of the term planet. As a result, there are various geophysical definitions in use among professional geophysicists, planetary scientists, and other professionals in the geosciences. Many professionals opt to use one of several of these geophysical definitions instead of the definition voted on by the International Astronomical Union. Some geoscientists adhere to the formal definition of a planet that was proposed by the International Astronomical Union (IAU) in August 2006. According to IAU definition of planet, a planet is an astronomical body orbiting the Sun that is massive enough to be rounded by its own gravity, and has cleared the neighbourhood around its orbit. Another widely accepted geophysical definition of a planet includes that which was put forth by planetary scientists Alan Stern and Harold Levison in 2002. The pair proposed the following rules to determine whether an object in space satisfies the definition for a planetary body. A planetary body is defined as any body in space that satisfies the following testable upper and lower bound criteria on its mass: If isolated from external perturbations (e.g., dynamical and thermal), the body must: Be low enough in mass that at no time (past or present) can it generate energy in its interior due to any self-sustaining nuclear fusion chain reaction (else it would be a brown dwarf or a star). And also, Be large enough that its shape becomes determined primarily by gravity rather than mechanical strength or other factors (e.g. surface tension, rotation rate) in less than a Hubble time, so that the body would on this timescale or shorter reach a state of hydrostatic equilibrium in its interior.