Pluto Got Robbed, Say Astronomers

It deserves to be a planet, say University of Central Florida researchers
By John Johnson,  Newser Staff
Posted Sep 10, 2018 7:49 AM CDT
A combination of images captured by the New Horizons spacecraft of Pluto.   (NASA/JHUAPL/SwRI via AP)

(Newser) – Pluto deserves to be a planet again, says new research out of the University of Central Florida. Scientists there think the 2006 rules used to boot Pluto from the planet club are bogus, and they recommend a different standard under which it would qualify, per a UCF release. The researchers specifically take issue with the International Astronomical Union's 2006 declaration that a celestial body is a planet only if it "has cleared the neighborhood around its orbit," meaning it's the "largest gravitational force in its orbit," in the UCF translation. Pluto does not meet that standard—but the UCF researchers say it's not supported in scientific literature, reports New Atlas. In fact, they found one only published study in the last two centuries using the clear-their-orbit standard to define a planet, and that 1802 study was based on now-debunked information.

"The IAU definition would say that the fundamental object of planetary science, the planet, is supposed to be defined on the basis of a concept that nobody uses in their research," says Phillip Metzger, lead scientist on the study, in Icarus. "It's a sloppy definition," he adds. "If you take that literally, then there are no planets, because no planet clears its orbit." The UCF team instead recommends that a celestial body deserves to be called a planet if it's big enough that its gravity shapes it into a ball, or sphere. That was one of three criteria the IAU listed in 2006, but Metzer thinks it should be the only one. It's "not just an arbitrary definition," he says. "It turns out this is an important milestone in the evolution of a planetary body, because apparently when it happens, it initiates active geology in the body." (Pluto's sky is similar to ours.)

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