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Pluto a Planet? New Research from UCF Suggests Yes
The reason Pluto lost its planet status is not valid, according to new research from the University of Central Florida in Orlando. In 2006, the International Astronomical Union, a global group of astronomy experts, established a definition of a planet that required it to "clear" its orbit, or in other words, be the largest gravitational force in its orbit. [...] [Philip] Metzger, who is lead author on the study, reviewed scientific literature from the past 200 years and found only one publication -- from 1802 -- that used the clearing-orbit requirement to classify planets, and it was based on since-disproven reasoning.
[...] The planetary scientist said that the literature review showed that the real division between planets and other celestial bodies, such as asteroids, occurred in the early 1950s when Gerard Kuiper published a paper that made the distinction based on how they were formed. However, even this reason is no longer considered a factor that determines if a celestial body is a planet, Metzger said.
[...] Instead, Metzger recommends classifying a planet based on if it is large enough that its gravity allows it to become spherical in shape. "And that's not just an arbitrary definition, Metzger 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, for instance, has an underground ocean, a multilayer atmosphere, organic compounds, evidence of ancient lakes and multiple moons, he said. "It's more dynamic and alive than Mars," Metzger said. "The only planet that has more complex geology is the Earth."
Planet Ceres, please.
The Reclassification of Asteroids from Planets to Non-Planets (DOI: 10.1016/j.icarus.2018.08.026) (DX)
Related: Pluto May Regain Status as Planet
Earth is a "Dwarf Planet" Because it has not Cleared its Orbit
(Score: 4, Interesting) by AthanasiusKircher on Saturday September 08 2018, @01:29PM (1 child)
You're right, there's nothing magical about any of these numbers. We're talking about SCIENCE here, not magic.
But actually, yes, there is something non-arbitrary about the number 1 here. It wasn't just chosen arbitrarily. If you actually read the original paper this metric was derived from (you notably seem to have ignored replying to my post, which dealt with the exact same issue), you'd see that the number was derived based on orbital mechanics and estimates about how a given body could clear an orbital neighborhood over the timespan of the main stellar sequence. Is that an "arbitrary" definition? Yes, in the sense that all definitions are ultimately arbitrary. But the number wasn't chosen for no reason at all, or just to exclude Pluto -- it was chosen to be meaningful both in our solar system and in other stellar systems where bodies might reasonably clear other objects around them in finite amount of time that's meaningful on the timescale of stars.
As the original article that defined that metric noted, one could choose 1/10th of the average main stellar sequence timespan as the metric, and then you'd have to increase mass by a factor of ~6. And you can tweak definitions of "orbit clearing," etc. in various ways. But they tried to come up with some reasonable standards, which had nothing to do with demoting Pluto or any other such nonsense. This is about coming up with a reasonable metric that would be useful for thinking about exoplanets, etc.
The GP wasn't confused. You are. GP in this context clearly meant inside the orbital region CLOSER TO THE SUN THAN the asteroid belt. Try reading again. And maybe try reading the original article that proposed the metric for clearing the neighborhood. You might learning something.
(Score: 1) by khallow on Sunday September 09 2018, @12:44PM
Sure, we are.