History repeating itself . . . Ceres / Pluto debate?

I think the article by James Hilton "When did the asteroids become minor planets?" on the US Naval Observatory website that I've referenced below is the best discussion I've seen on the topic.

My summary is that in the 1850's the discovery rate of objects in orbits between those of Mars and Jupiter began to pick up, leading to the dawning realisation that there were was a whole belt of objects out there.

There was less of a debate in the 1850s. But the parallel is even stronger.

When Ceres was first discovered, astronomers didn't know of the other asteroids. So they thought Ceres was alone. It seemed to make sense to consider it a planet--though a very smalll one. Then they discoevered others--Juno, Pallas, Vesta, etc. It bacame clear that Ceres was only one of many small bodies orbiting between Mars and Jupiter--so they invented a new categorie--the asteroids.

Not unlike the whole Pluto thing. For decades, Pluto was the only object we knew about that orbited past Neptune. And although small, and with an odd orbit, it seemed to fit the definition of a planet. Then, a couple of decades ago, astronomers began to detect similar objects out past Neptune--and its' become clear Pluto is just the closest (and one of the largest) of these objects--which are now known collectively as the Kyber Belt--and the larger members, like Pluto, are in a new category: dwarf planets.

Herschel who had discovered Uranus in 1781 (and its 2 largest moons and 2 further moons of Saturn) felt that Ceres when it was discovered in 1801 was disappointingly small compared to the other planets.

When 2 Pallas was found in 1802 and was even smaller. and it too was hailed as a planet Herschel invented the term "asteroid" (meaning "star-like") and hoped therefore to prevent a proliferation of planets.

After 3 Juno (1804) and 4 Vesta (1807) were found no more were discovered till the 1840s. But by the mid-1850s the total number of asteroids had reached 15 and until they were all removed from planetary status the number of planets we had thereby acquired was 23 (6 classical planets plus Uranus and in 1846 Neptune)

There was no IAU till the 1920s but even so a concensus was arrived at that 23 was too many planets to contemplate having on board, Just as well that they acted decisively as numbers topped 100 by 1868, reached 400 before the 20th century had even dawned and as of April 2007 there are now hundreds of thousands of asteroids that have been discovered within the solar system. As of March 3, 2007, a total of 368,650 registered minor planets within the solar system and the present rate of discovery is about 5000 per month.

As of March 3, 2007, 152,554 have orbits known well enough to be given permanent official numbers. Of these, 13,627 have official names.

Current estimates put the total number of asteroids above 1 km in diameter in the solar system to be between 1.1 and 1.9 million. The largest asteroid in the inner solar system is 1 Ceres, with a diameter of 975 to 909 km. Two other large inner solar system belt asteroids are 2 Pallas and 4 Vesta; both have diameters of ~500 km. Vesta is the only main belt asteroid that is sometimes visible to the naked eye (in some very rare occasions, a near-Earth asteroid may be visible without technical aid; see 99942 Apophis).

The mass of all the asteroids of the Main Belt is estimated to be about 3.0-3.6×1021 kg, or about 4% of the mass of our moon. Of this, 1 Ceres comprises 0.95×1021 kg, some 32% of the total. Adding in the next three most massive asteroids, 4 Vesta (9%), 2 Pallas (7%), and 10 Hygiea (3%), brings this figure up to 51%; while the three after that, 511 Davida (1.2%), 704 Interamnia (1.0%), and 3 Juno (0.9%), only add another 3% to the total mass. The number of asteroids then increases rapidly as their individual masses decrease.