A recent proposal by three astronomers suggests redefining what constitutes a planet in astronomy. The current definition, established in 2006 by the International Astronomical Union (IAU), requires a celestial body to orbit the sun, clear its orbit, and have enough mass to be nearly round in shape to be considered a planet. However, this definition does not include planets orbiting stars other than our sun.
The new proposal aims to expand the definition to include exoplanets, which are planets orbiting stars outside our solar system. The proposed definition focuses on a planet’s mass, with specific limits to determine whether a celestial body qualifies as a planet. For example, a planet must be lighter than 13 Jupiters to be classified as such. This mass-based approach aims to provide a more objective criterion for defining planets, removing ambiguity about a planet’s shape or orbit.
The researchers emphasize the need for a revised definition that can be applied to any celestial body orbiting a star, stellar remnant, or brown dwarf. They argue that the current definition’s requirement for planets to be nearly round is challenging to implement, especially for distant worlds whose shapes cannot be accurately determined. By anchoring the definition to mass, the proposed criteria aim to simplify the classification of planets and encourage discussions within the scientific community about what truly defines a planet.
Notably, the proposed definition would not change the status of Pluto, which was reclassified as a dwarf planet in 2006. Pluto’s mass falls below the lower limit suggested by the new definition, meaning it would continue to be classified as a dwarf planet under the proposed criteria.
While the International Astronomical Union has not yet commented on the proposed definition, lead researcher Jean-Luc Margot is set to present the proposal at the IAU General Assembly next month. Changes to the official definition of a planet would require a vote by IAU members during the assembly.
Overall, the proposed mass-based definition of planets in astronomy seeks to modernize and clarify the criteria for classifying celestial bodies as planets, particularly those orbiting stars beyond our solar system. By establishing specific mass limits, the new definition aims to provide a more objective and practical approach to defining planets, sparking conversations within the scientific community about the nature of planets in the universe.
