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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 theluggage on Saturday September 08 2018, @03:02PM (3 children)
Historically, "planet" has also referred to any object that moved against the "fixed background" of stars, which would cover anything up to and including Russel's Teapot. Between 1930 and 2006 "planet" included Pluto - so what changed between 1846 and 1930?
Beyond what radius/volume does a "small ball of rock" become a "big ball of rock"? Just bigger than Pluto? Or should it go by mass (a bit more massive than Eris)?
So, sorry, your argument depends on "Historical" meaning "discovered before Pluto" and "big" meaning "bigger than Pluto". Not very scientific.
If you want a "traditional" definition of "planet" just say "the planets are - by tradition - Mercury, Venus, Earth, Mars, Jupiter, Saturn, Neptune and Uranus" and, I dunno, maybe use trial by combat to decide whether to include Pluto - or ask that octopus that predicts the superbowl winner. That's fine - just be upfront that its a historical artefact rather than scientific definition and don't try and pass off an arbitrary line in the sand as "science".
As TFA argues: if you want a science-based definition, the "gravity strong enough to form a spheroid" criteria at least has some scientific significance.
Problem is, at some stage the argument is going to have to turn to the categorisation of exoplanets (and there's already more known exoplanets than planets - fortunately, so far, they tend to be firmly in the big-balls-of-whatever category because we can't see the small ones - yet). Then, we'll have exoDwarfPlanets and will need to use CamelCase to make it readable - and nobody wants to see that!!!
All hail planet Eris - except it obviously should be called Rupert [wikipedia.org] - the IAU just can't get it right, can they?
(Score: 2) by isostatic on Saturday September 08 2018, @03:36PM (2 children)
Historically, "planet" has also referred to any object that moved against the "fixed background" of stars,
Historical as in since man first looked up at the stars and saw wanderers - pre Galileo
Beyond what radius/volume does a "small ball of rock" become a "big ball of rock"? Just bigger than Pluto? Or should it go by mass (a bit more massive than Eris)?
Both size and mass wise the jump between Pluto/Eris and Mercury is enormous, more than the distance between them and Makemake/2007 OR10, and we believe we'll be finding far more objects in that region.
I don't mind if you want to include Pluto in your definition of Planet, however you have to include Eris and any other similar objects as well. We then just need a new term to define "big planets".
(Score: 0) by Anonymous Coward on Saturday September 08 2018, @07:15PM
That's OK. If they meet the criteria for a "planet" then they should be called a "planet".
Hmm ... why? What's the difference between a "planet" and a "big planet"? Why would we need to distinguish between them?
(Score: 2) by theluggage on Saturday September 08 2018, @08:29PM
Lets see - looks up some numbers on Wikipedia - I make Pluto 49% of the size of Mercury... and once you add in the larger moons there's severalin-between sized rocky balls in the solar system. On the other hand, Uranus a mere 44% of the size of Saturn and there is nothing in between. That's not to mention the fricking huge quantum leap in diameter and mass between Earth and Neptune... If exoplanet-detection technology improves so that Astronomers can be sure that they're not just picking up the oddities then either the gaps will get filled in or the real, physical distinctions will show up.
Is anybody saying otherwise? Its the Pluto-demoters who argue against Eris etc. being planets.