Dwarf planets are all those other planet like bodies in the solar system that somehow resemble the eight planets. Once there were nine planets but Pluto got demoted from a planet to the status of a dwarf planet. The special characteristics that make up a planet, and they're one all dwarf planets meet, is having enough substance to round themselves out into a ball like structure, and simply not to float around up there in any old ragtag fashion but to have some kind of consistency to their movements. To do this there must be gravity. That is the capability to attract other particles and substances and the ability, by protective rings, or other methods, of holding on to their substance after it has been collected.
Order and the ability to attract and to forge ahead and instill balance wherever possible is as important to the solar system as it is to the earth. In fact, earth is the third planet from the sun. The first two are Mercury, Venus. Mars is the fourth, followed by Jupiter, Saturn, Uranus and Neptune. In between Mars and Jupiter, on the planet and planet-like chart is Ceres, a dwarf planet. It is so placed because it not as close to the sun as Mars, but is closer to the sun than Jupiter.
After Neptune, the eight planet, there are six listings of forms taking up space in the atmosphere and on the charts. They are listed only by a number and a couple of letters. and then the name Orcus appears, and below that is Pluto. On down the line in distances from the sun are Ixion, Huya, Quaoar, Eris and Sedna. And in between those are other number and letter designations of something's. Most of these have not been fully explored and therefore little is known about them.
How many dwarf planets are out there? Three. Yes, only three, of all the other asteroids, or whatever, only three meet the qualifications to be called dwarf planets. The others are probably irregular shaped boulders or some other kind of body. Yet of the three, only Ceres is round, and even that is contradictory information about what makes a planet designated a dwarf. Others may be, but not much is known about their shapes or their characteristics.
As outer space is further explored and new information is learned, lots more knowledge about designating this or that as an asteroid, or whatever, will be forthcoming. The most recent place that has a lot of unknowns are the Kuiper belt, a farther distance away from the sun and way beyond Neptune. It is possible many icy objects will be found there that will classify as dwarf planets, if the truth will ever be known.
Exactly why did Pluto get demoted to a dwarf planet? According to NPR (National Public Radio) it happened like this: A California Institute of Technology astronomer killed it. Asked by an interviewer why he did it, Professor Mike Brown answered: Pluto should never have been a planet in the first place. In 1930, those the who designated Pluto the eight planet was wrong. In other words, the honest professor was only righting a wrong.
How did the professor discover this fact? He was looking for a tenth planet and what he found, way beyond Pluto, was something much larger and a whole unexplored area known as the Kuiper belt area. He then went back and loped Pluto off the list. Mike Brown's book, where more information can be found is "How I Killed Pluto and Why It Had It Coming."