Last week, three astronomers proposed expanding the official definition of a planet to include worlds orbiting stars other than Earth, a nuance that’s not currently included in the official definition of a planet established by the International Astronomical Union (IAU) in 2006. If their new definition goes ahead, thousands of objects in the universe could be officially identified as planets.
According to the current IAU definition, for an object to be considered a planet it must orbit the Sun, clear an area around its orbit, have sufficient mass, and gravity To be a planet, it would have had to be sculpted into a roughly round shape. The third criterion is particularly vague because it doesn’t quantify how round an object should be, according to a team led by UCLA astronomer Jean-Luc Margot.
“Earth is not perfectly round, so how round does a planet have to be?” Brett Gladman, an astronomy professor at the University of British Columbia and co-author of the study, wrote in a recent paper. statement“When we look at planets orbiting other stars with our current technology, we can’t measure their shapes.”
The researchers also say some aspects of the current definition are too specific, since it requires that planets must orbit the Sun, and excludes the thousands of planets that orbit other planets. Performer There are several celestial bodies in the universe that meet the criteria to be called planets.
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“We now know that there are thousands of ‘planets’ orbiting other stars, but the IAU definition only applies to planets in our solar system, which is clearly a major flaw,” Margot said. “We propose a new definition that can be applied to objects orbiting any star, stellar remnant, or brown dwarf.”
in paper In a paper posted to a preprint server on July 10 and soon to be published in the Journal of Planetary Science, Margot and his colleagues propose determining an object’s planetary status based on its mass. According to the proposed definition, a world could be called a planet if it was within a certain mass limit — for example, it would need to be lighter than 13. Jupiterbeyond which nuclear fusion begins and the object is no longer a planet but becomes what is called a quasi-stellar. Brown dwarf.
“By fixing the definition on the quantity that is most easily measured – mass – we eliminate any debate about whether a particular object meets the criteria,” Gladman said. “This is the weakness of the current definition.”
PlutoThe planet, which was downgraded to a dwarf planet in 2006 after a heated IAU debate, will remain a dwarf planet because it is lighter than the minimum limit set by the newly proposed definition. Dwarf planet.
Moreover, Margot and his team argue that the current IAU definition, which requires planets to be “nearly round” in shape, is difficult to implement and effectively useless because it cannot reliably resolve the shapes of many distant planets. Instead, by using a mass-based threshold, “we replace vague and unrealistic specifications for roundness,” the researchers write in their new paper.
“We’re putting numbers on these definitions, drawing lines around them, and encouraging the community to start the discussion. teeth A planet?’” Gladman said.
The IAU has not yet announced any potential changes to its official planet definition. UCLA’s statement said Margot plans to present the proposed definition at the IAU General Assembly in Cape Town, South Africa, next month. IAU resolutions are typically voted on by members at the General Assembly.
