Three astronomers last week proposed expanding the official definition of a planet to include worlds orbiting stars other than our own, a nuance not currently included in the official definition of the term established in 2006 by the International Astronomical Union, or IAU. If the new definition of the trio pans out, thousands of celestial bodies across the universe could be confirmed as official planets.
For a celestial body to qualify as a planet under the current IAU definition, it must orbit the sun, must have cleared the area around its orbit, and must have enough mass that its gravity would have sculpted it into a nearly spherical shape. round so that it is a “planet”. The third requirement is particularly vague because it does not quantify how round the celestial body must be, according to a team led by astronomer Jean-Luc Margot of the University of California, Los Angeles (UCLA).
“The Earth is not perfectly round, so how round does a planet have to be?” Study co-author Brett Gladman, who is a professor of astronomy at the University of British Columbia, said in a recent. STATEMENT. “If you look at a world orbiting another star, with current technology, we can’t measure the shape.”
The researchers also say that some aspects of the current definition are too specific, such as the one that requires planets to orbit our sun because it excludes thousands of worlds around other stars in the universe that otherwise meet the criteria to be called planets.
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“We now know of thousands of ‘planets’ orbiting other stars, but the IAU definition only applies to those in our own solar system, which is clearly a major flaw,” Margot said. “We propose a new definition that can be applied to celestial bodies orbiting any star, stellar remnant, or brown dwarf.”
In one paper posted on a preprint server July 10, soon to be published in the Planetary Science Journal, Margot and his colleagues propose determining the planetary status of a celestial object based on its mass. According to the proposed definition, a world can be called a planet if it is within certain mass limits. For example, it should be lighter than 13 Jupiters, beyond which nuclear fusion begins and the object is no longer a planet, but a substar called a brown dwarf.
“Having definitions anchored in the most easily measurable quantity—mass—removes arguments about whether or not a specific object meets the criterion,” Gladman said. “This is a weakness of the current definition.”
Pluto, which in 2006 was demoted to a dwarf planet in a much-debated decision by the IAU, would be lighter than the lower limit suggested by the newly proposed definition, and would thus continue to remain a planet. dwarf
Furthermore, the current IAU definition requiring planets to have “nearly round” shapes is difficult to enforce, Margot and his team argue, and is thus effectively useless since the shapes of many distant worlds do not can be safely resolved. Instead, using mass-based thresholds would “replace a vague and impractical prescription regarding roundness,” the researchers write in the new paper.
“We’re drawing a line in the sand by putting some numbers on these definitions, to encourage our community to start the discussion: What exactly IS a planet?” Gladman said.
The IAU has so far made no announcement of possible changes to its official definition of a planet. The UCLA statement noted that Margot is scheduled to present the proposed definition next month at the IAU General Assembly in Cape Town, South Africa. IAU resolutions are usually voted by its members during general assemblies.