Is Pluto a Planet, or What? By Brian Simpson

Here is an article for our numerous readers who have an amateur interest in astronomy and astro-physics, which keeps people like me off the street, and looking at the stars. Pluto was demoted as being a planet, but not all agree with this, since it is not orbiting another planet as a moon, and just because it is small, well, small is relative. Just look at that bully Jupiter.

https://phys.org/news/2018-09-pluto-reclassified-planet.html

https://www.space.com/41769-pluto-planet-definition-debate-rages-on.html

https://theconversation.com/curious-kids-is-pluto-a-planet-or-not-133738

https://www.sciencedirect.com/science/article/pii/S0019103518303063

“Scientists have spent 12 years arguing over how to classify Pluto, and a recently published paper offers a new — but surprisingly old — reason for restoring the object's planetary status.

The new research focuses not on any qualities of celestial bodies themselves but on the past 200 years of scientific literature. Four scientists trawled through astronomy papers published since 1802 looking for instances of the word planet used as defined by the controversial 2006 verdict from the International Astronomical Union (IAU) that reclassified Pluto as a dwarf planet. That group is responsible for handling astronomical nomenclature. The definition included the requirement that planets "clear" their orbit, making them the gravitational big shots in their neighborhoods.

"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," lead author Philip Metzger, a planetary scientist at the University of Central Florida, said in a statement released by the university.

The new research focuses on how scientists over the past two centuries have discussed asteroids. This term was used interchangeably with "small planets" or even just "planets" up until the early 1950s, the investigators found.

The authors argued that the IAU's definition, which the group voted on during its annual conference in 2006, attempts to override long historical usage in the community. "We recommend that, regarding planetary taxonomy, central bodies such as the IAU do not resort to voting to create the illusion of scientific consensus," the authors wrote. "The IAU has done damage to the public perception of science, which is a process free from centrally dictated authority, in its imposition of a definition of planet and the number of planets fitting that definition, which has been instilled in educational textbooks around the world on the basis of their authority."

(The authors didn't comment on the fact that plenty of very definitely nonplanet objects have been referred to as planets over the history of scientific discourse, up to and including the sun.)

The definition agreed upon at that IAU meeting requires that an object meet three conditions to qualify as a planet: It must orbit the sun, it must be massive enough that its gravity pulls it more or less into a spherical shape, and it must clear the neighborhood around its orbit. Metzger and his co-authors argued that the third piece of that definition does not match historical usage by scientists and should be revoked.”