A UCLA professor has proposed a new definition of what constitutes a planet, one that he says is simpler and more objective than the current definition.
The current definition, adopted by the International Astronomical Union (IAU) in 2006, states that a planet is a celestial body that:
* Is in orbit around the Sun
* Has sufficient mass to assume hydrostatic equilibrium (a nearly round shape)
* Has "cleared the neighborhood" around its orbit
The third criterion is the most controversial, as it is not always clear what it means to have "cleared the neighborhood." Some astronomers argue that Pluto should still be considered a planet because it has not completely cleared its orbit of other objects, while others argue that it should be reclassified as a dwarf planet.
The new definition, proposed by UCLA professor Alan Stern, does away with the third criterion. Instead, Stern proposes that a planet be defined simply as a celestial body that:
* Is in orbit around the Sun
* Has sufficient mass to assume hydrostatic equilibrium
Stern argues that this definition is simpler and more objective than the current definition, as it does not require astronomers to make subjective judgments about what it means to have "cleared the neighborhood."
Stern's definition would reclassify Pluto as a planet, as it meets both of the criteria. However, it would also reclassify many other objects in the solar system as planets, including the dwarf planets Ceres, Eris, Haumea, Makemake, and Sedna.
Stern's proposal is likely to be controversial, as it would change the way that we think about the solar system. However, it is a well-reasoned argument that deserves to be considered.
Pros and cons of Stern's proposed definition
There are a number of pros and cons to Stern's proposed definition of a planet.
Pros:
* Simpler and more objective: The new definition is simpler than the current definition, as it does not require astronomers to make subjective judgments about what it means to have "cleared the neighborhood."
* More inclusive: The new definition would reclassify Pluto and other objects in the solar system as planets, which would make the solar system more diverse and interesting.
* Consistent with scientific understanding: The new definition is consistent with our current scientific understanding of the solar system.
Cons:
* Not consistent with the IAU's definition: The new definition is not consistent with the IAU's definition, which is the internationally recognized definition of a planet.
* Could lead to confusion: The new definition could lead to confusion, as it would change the way that we think about the solar system.
Conclusion
Stern's proposed definition of a planet is a well-reasoned argument that deserves to be considered. However, it is likely to be controversial, as it would change the way that we think about the solar system.
