An excellent feature of the book "Is Pluto a Planet? A Historical Journey through the Solar System" by David A. Weintraub is it shows how often the list and number of planets has changed through human history.
The Greeks thought the Sun was the planet and the Earth was not.
Vulcan was a planet that ninetheen century smart people believed in and earnestly expected to be found to explain oddities in Mercury's orbit. Vulcan wasn't found. Einstein's theory of relativity explained and accurately predicted the oddity of Mercury.
As more and more moons of planets were found, they were called planets too, until it seemed like they were too many and they were called moons and not planets. That is, it was decided, after asteroids started being noticed in quantity, that to be called a planet the object had to directly orbit the sun, not orbit something orbiting the sun--and so of course orbet the sun itself.
Same thing with asteroids--the first found were called planets but then there seemed to be too many, so they were called asteroids, or minor planets.
"Is Pluto a Planet?" is good with that historical perspective of changing ideas of what a planet is. It is good also to read to get a feel for the many objects and many kinds of objects that are orbiting the sun, as we are.
I like when he talks about "the object we call Pluto." There are lots of objects out there; what we call them varies; their amazingness and beauty does not.
David Weintraub being a professional planet studier, he often gets asked the question who used to name his book: Is Pluto a planet?
He really likes the question because gives him a chance to talk about all the different kinds of objects in the solar system, how we noticed them, what we've named them, what they are like.
I feel reading his book sometimes part of a grand procession around the sun, sometimes part of a gangling group. Hundreds of asteroids, eight or nine biggish to gigantic planets, and now we're just starting to notice the beyond Pluto group, which many think includes Pluto--the Kuiper Belt Objects. We've noticed few--there are very probably many more to notice.
Pluto kind of had a slow motion treatment like the first asteroids got. Ceres, a large for an asteroid asteroid noticed early was felt to be a planet by many until folks got a feeling for how many asteroids there are. Pluto was the outermost planet for a good long time because star scientists theorized and then found the Kuiper Belt.
When things we call planets in our solar system threaten to rise to number far above ten we humans feel that is not okay and make new rules to keep the count down.
But the many objects revolving are there before and after we notice them, and I get to live on one in part of the large, slowly being revealed, elliptical parade.