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Dr. Phil Metzger @DrPhiltill
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To be clear: our new paper shows that asteroids were reclassified as non-planets not on the basis of orbit-sharing, but their geophysical properties: they are unlike planets. The argument in 2006 (that they were reclassified because of orbit sharing) is factually untrue. /1
2/ If we apply the exact same standard to Pluto that we applied to asteroids, then it is most definitely a planet. This is what the published scientific record shows.
3/ The standard that was applied to asteroids, first in thinking they were planets, later in realizing they should not be, was completely in-line with the geophysical definition of a planet that came down to us from Galileo in the Copernican Revolution.
4/ Before the Copernican Revolution, planets were a dynamical category of "stars" (lights in the sky). The planets (including the sun and Moon) were the 7 "stars" that moved in regular patterns around the Earth. In ancient times they were gods, each ruling its own sphere.
5/ At the Copernican Revolution, the establishment thought there were two different physics: one physics for Earth and a different physics for the heavens. The planets were part of the heavenly physics.
6/ Galileo pointed his telescope at the Moon and saw mountains. He argued the Moon is a geophysical body like Earth. Geo=Earth. Physical=physics. Thus, the heavens have the same physics as Earth. Since the Moon was a planet, he extrapolated all the planets are geophysical bodies.
7/ He thus proved the Earth is in the heavens, so it orbits the sun. But the Moon orbits the Earth and he still called it a planet. And he found four moons of Jupiter and he called them planets. Note well: Galileo redefined "planet" from a dynamical category to a geophysical one.
8/ In other words, Galileo did not care that the planets are in different dynamic states. It didn't matter that they orbit the sun or something else. Dynamics was no longer the defining characteristic of a planet. Being a body "like the Earth" was the new defining characteristic.
9/ This Galilean definition of a planet has defined Planetary Science for 400 years. This is what is at stake in the IAU's definition of a planet. It's not mainly about Pluto. It's about Galileo's legacy. It's about undoing the taxonomical progress of the Copernican Revolution.
10/ If we say a body has to be dominant to be a planet, we are injecting a cultural expectation into science. We are saying planets "ought" to be a few bodies that rule in their own spheres like gods. Why? Because culture expects it. Even though it is not useful in science.
11/ No scientist is writing papers about how the geochemistry of orbit-clearing planets is different from those that fail to clear their orbits. Nobody is studying how it makes their atmospheres different, or their cores, or mantles, or, or,... Orbit-clearing is 99.9% irrelevant.
12/ Galileo put planetary science firmly on the basis of geophysics. An orbit clearing definition undoes that. It takes away the central geophysical word of our science ("planet") and gives it to a narrow dynamics concept that is not useful for 99.999% of people studying planets.
13/ There's a LOT more that can be said about this... (stepping off soapbox) 😅
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