Pluto should be classified as a planet again, say scientists

Mindy Sparks
September 12, 2018

In 2006, during their 26th General Assembly, the International Astronomic Union (IAU) passed a resolution to adopt a formal definition for the term "planet".

Originally called Planet X, Pluto was a massive discovery both as a new planet and for the Lowell Observatory's latest camera and photography systems.

The IAU defines a planet as having the largest gravitational force in its orbit, which disqualifies Pluto because it is under the influence of Neptune's gravity. However, in a new paper published August 29 in the journal Icarus, Florida Space Institute researcher Philip Metzger and co-authors reported that this standard for classifying planets is not supported in the scientific literature.

"It's a sloppy definition", Metzger continued, talking about the IAU's definition.

Experts now say Pluto should be reclassified as a planet, suggesting that the icy dwarf should be a planetary body. "If you take that literally, then there are no planets, because no planet clears its orbit".

Metzger and his team looked at more than two centuries' worth of research and found just one study, from the early 19th century, that employed the orbit-clearing standard the IAU used to downgrade Pluto. He said it was based on reasoning that has since been disproved.

"Clearly I have a totally nonscientific bias in favor of the old designation", Twarog said.

"We now have a list of well over 100 recent examples of planetary scientists using the word planet in a way that violates the IAU definition, but they are doing it because it's functionally useful", he said. Stars, asteroids, meteorites, black holes would still be ruled out, but that would up the number of so-called planets in our solar system from eight to-wait for it-110.

Moons such as Saturn's Titan and Jupiter's Europa have been called planets by scientists since the time of Galileo.


Set against this backdrop, he believes that the IAU definition of what constitutes a planet needs to be rethought.

The new definition, they argue, would meet the needs of both scientific classification and "peoples' intuition".

'We showed that this is a false historical claim, ' Runyon said.

In short, their definition would apply to any astronomical body that has achieved hydrostatic equilibrium, which not only applies to Pluto but most of the Solar System's largest moons. Metzger recommended changing the definition to include the planets intrinsic properties rather than the status of a planet's orbit. Today, the debris and asteroids that fall into Pluto's path are many, but they may disappear a billion years from now - so they shouldn't be fundamental to describing a body.

"And that's not just an arbitrary definition", he said. "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, he notes, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons.

"It's more dynamic and alive than Mars", Metzger says.

"Any revision which places Pluto back where it belongs among the other planets is welcome", Twarog said.

Certainly, this isn't the last word, but the lively debate is valuable and useful.

Other reports by Iphone Fresh

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