The stuff in the Solar System is now divided into 4 main categories. The first 3 are, in order of decreasing size: Planets, Dwarf Planets, and Small Solar System Bodies. All of those orbit the Sun. The 4th category is the Moons, which orbit planets instead of the Sun.
Planets: For something to be a planet, it has to be big and round, it has to orbit the Sun, and it has to have done a pretty good job of cleaning smaller things out of its orbit. (Clean your room, Sammy!) There are 8 planets right now. Four have surfaces you could stand on (Mercury, Venus, Earth, Mars), and 4 are big balls of gas (Jupiter, Saturn, Uranus, Neptune). These gas giants might have a rock/ice core waaaaay down in the center, but to get there you'd have to go through a very deep ocean of either metallic hydrogen (JS) or ammonia-methane-water (UN). No fun!
Dwarf Planets: It's counterintuitive, but Dwarf Planets don't count as "Planets". A Dwarf Planet is big enough to be round, but too small to have really cleaned up its orbit. If you were standing on one, it would probably be a lot like the surface of a moon. To pay homage to Pluto, the Dwarf Planets near/beyond the orbit of Neptune are called Plutoids. At the moment there's only one Dwarf Planet that's not a Plutoid: That's Ceres, which orbits in the Main Asteroid Belt between Mars and Jupiter.
Small Solar System Bodies: Includes Asteroids and Comets. These are smaller and generally oddly-shaped (sometimes like potatoes). Asteroids are made of rock/iron, and comets are made of rock/ice. When a comet gets too close to the Sun, it heats up and the ice melts and evaporates, making for a very pretty Coma as well as a long gassy Tail (actually, more than one tail!).
Here are the names of the current Plutoids:
- Pluto
- Haumea
- Makemake
- Eris
Here are the names of some objects that might someday count as Plutoids (scientists don't know if they're big/round enough yet):
- Orcus
- Ixion
- Huya
- Varuna
- Quaoar
- Sedna
Here are the names of smaller things with names, orbiting the Sun out near Neptune:
- Logos
- Chaos
- Rhadamanthus
- Deucalion
- Borasisi
- Teharonhiawako
- Ceto
Sammy, you asked about something named Cygna? I guess you meant Sedna! The names of everything listed above are either Creation or Underworld gods in different cultures throughout history. Well, actually, some of them are just so far from the Sun that they're just named for things that are COLD. For example, Sedna is the Inuit goddess of the sea (the Arctic Ocean)!
