Why isn’t a dwarf planet still a planet?:
When Pluto was excluded from the planetary display in 2000 at the American Museum of Natural History in New York City, children sent hate mail to Neil deGrasse Tyson, director of the museum’s planetarium. Likewise, there was a popular uproar when 15 years ago, in August 2006, the International Astronomical Union, or IAU, wrote a new definition of “planet” that left Pluto out. The new definition required that a body 1) orbit the sun, 2) have enough mass to be spherical (or close) and 3) have cleared the neighborhood around its orbit of other bodies. Objects that meet the first two criteria but not the third, like Pluto, were designated “dwarf planets.”
Lisa Grossman, “The definition of planet is still a sore point – especially among Pluto fans” at ScienceNews
Grossman cites scientists pro and con, and then notes,
But since 2006, we’ve learned that Pluto has an atmosphere and maybe even clouds. It has mountains made of water ice, fields of frozen nitrogen, methane snow–capped peaks, and dunes and volcanoes. “It’s a dynamic, complex world unlike any other orbiting the sun,” journalist Christopher Crockett wrote in Science News in 2015 when NASA’s New Horizons spacecraft flew by Pluto.
Lisa Grossman, “The definition of planet is still a sore point – especially among Pluto fans” at ScienceNews
She adds, “The truth is, there’s no single definition of a planet — and I’m beginning to believe that’s a good thing.”
Dumping Pluto as a planet just added needless complexity to the system — for all the people who don’t live this stuff. At least it gave the people who do live this stuff something to do.