Recently Pluto has been demoted to dwarf planet, and some have feared that it would be removed out of science textbooks since it's no longer a planet - well I would like to make a suggestion - why not include all worlds in science textbooks - there are fascinating worlds that are not planets, like Io, Europa, Titan, and Triton. Instead of only eight planets, we would have atleast 41 worlds in our solar system.
The 42 worlds are Mercury, Venus, Earth, Moon, Mars, Ceres, Jupiter, Io, Europa, Ganymede, Callisto, Saturn, Mimas, Enceladus, Tethys, Dione, Rhea, Titan, Iapetus, Uranus, Miranda, Ariel, Umbriel, Titania, Oberon, Neptune, Triton, Orcus, Pluto, Charon, Ixion, Huya, Varuna, 2002 TX300, Haumea, Quaoar, Makemake, 2002 AW197, 2007 OR10, Eris, 1996 TL66, and Sedna. On this list of worlds, I've included all planets, round moons, and dwarf planets, as well as potential dwarf planets that are very likely above 500 miles in diameter and those that have been tested for roundness.
There are also many objects that may be on the border line (where it is hard to say if it is a world or not) - some of these are mentioned in the list below, but not counted on the list of worlds above (until more is known about them). Border line cases include Vesta and several others, many of them have estimated diameters that vary around or below 500 miles. Ungravitized objects could be called ACOs (or asteroid class objects), they include all small solar system bodies that are clearly not dwarf planets as well as non-round satellites.
The inner solar system consists of 5 worlds and several ACOs, all of the worlds are clearly notable objects in this region - four of them are planets, while the other is our moon. All five of these rocky worlds were known since ancient times.
Mercury - (planet) at 3032 miles across. This airless cratered world has scorching days and frigid nights.
Venus - (planet) at 7521 miles across. Venus has a thick choking atmosphere of carbon dioxide with traces of sulfuric acid. Temperatures are hot enough to melt zinc. It is known as the Morning and Evening Star.
Earth - (planet) at 7926 miles across. Earth has a nitrogen/oxygen atmosphere, has oceans of water, and land made of silicates. It also has life. Earth has one moon, the moon itself.
Moon - (moon) at 2160 miles across. Formally called Luna, it is the Earth's moon. The moon is an airless cratered world.
Mars - (planet) at 4222 miles across. It has a red surface with occasional global sand storms, it also has a thin atmosphere of carbon dioxide. Mars has two moonlets, the ACOs Phobos and Deimos.
The various ACOs in this region are Mars's two moonlets and the various Apollo asteroids and their kin.
The asteroid belt contains 1 (possibly 2) worlds, and hundreds of thousands of ACOs, Pallas is the largest ACO in the asteroid belt - it is about the same size as Vesta.
Vesta - (possible dwarf planet) is about 350 miles wide and 285 miles polar (pole to pole measure). It has a giant crater near its south pole which affects its overall shape (oblate spheroid with a chunk missing). Vesta is on the border of being a world or an ACO, if it can be shown that it is truly a world, then it would also be counted as a dwarf planet, it is a significant member of the asteroid belt. I'll give Vesta a 50% chance of being a world.
Ceres - (dwarf planet) is about 590 miles wide and is nearly the size of Saturn's moon Tethys. It is spherical and is clearly a world. It is obviously a significant member of the asteroid belt, since it is the largest. It has a surface of rock and ice, and a mantle of ice. Ceres is usually called an asteroid, but it is not an ACO.
All of the other asteroids (except Pallas (330 miles - egg shaped) and Hygiea (252 miles)) are under 250 miles across.
This region consists of four giant planets, their rings and satellites (many of which are worlds), the centairs (ACOs of this region which usually resemble comets), some comets, and the trojan asteroids of Jupiter and Neptune. The only worlds here are the four planets and many of their satellites, all other satellites and objects are ACOs.
Jupiter - (planet) at 88846 miles across, is the largest planet in our solar system. It is a gasious planet with a deep hydrogen atmosphere. It's cloudtops form bands around the planet as well as several hurricane like spots, of which the Great Red Spot is the most famous. Jupiter has smoke like rings, and 63 known satellites of which 4 are worlds (moons), the others are ACOs (moonlets).
Io - (moon) at 2264 miles across, it is a yellowish volcanic moon of Jupiter - actually it sort of looks like a spherical pizza and is so active it is nearly turning itself inside out. Its surface is primarily made of sulfur. The caldera (black lava pools) are hotter than Venus, while the rest of the world is frigid cold.
Europa - (moon) at 1940 miles across, it is an icy moon of Jupiter, that is believed to have an ocean of water under its crust. Its surface consists of grooves, and broken ice slabs. Europa is the most likely world in our solar system outside of Earth to contain life (none has been found though).
Ganymede - (moon) at 3270 miles across, it is the largest moon in the solar system. It is a brownish world of rock and ice with ridges and craters on its surface. It also has a magnetosphere.
Callisto - (moon) at 2996 miles across, it is a dark colored moon of Jupiter with bright icy craters all over. Its surface is surprisingly smooth considering how cratered it is. It also has spires on its surface.
Saturn - (planet) at 74898 miles across, is the most stunning planet due to its enourmous ring system. It is a gaseous planet like Jupiter, but has haze in its atmosphere. It also has fierce winds. Saturn has 59 known satellites, of which 7 are worlds, the others are ACOs. It is somewhat flattened at the poles due to its fast rotation.
Mimas - (moon) at 244 miles across, it is a rugged cratered moon of Saturn. It is elongated somewhat due to Saturn's tidal forces on it. It also has an enormous crater, making it resemble Star Wars's Death Star.
Enceladus - (moon) at 309 miles across, is a smooth bright icy moon of Saturn. It has geyser activity in its southern hemisphere. It is very spherical for its size.
Tethys - (moon) at 659 miles across, is a cratered icy moon of Saturn. It also has canyons.
Dione - (moon) at 696 miles across, is a cratered icy moon of Saturn.
Rhea - (moon) at 951 miles across, is a cratered icy moon of Saturn.
Titan - (moon) at 3200 miles across, it is an orange colored moon of Saturn with a thick atmosphere. Its surface is mainly methane and ice. It has dunes on its surface and is believed to have lakes in the polar regions.
Iapetus - (moon) at 907 miles across, it is a moon of Saturn with areas as dark as asphalt and areas as white as snow. It also has a strange equatorial ridge that gives it a walnut like shape.
Uranus - (planet) at 31763 miles across, it is a bluish ice giant with a thick atmosphere. It also has several thin rings. Uranus has 27 satellites of which 5 are worlds. Uranus is tilted on its side.
Miranda - (moon) at 293 miles across, it is a crazy looking moon of Uranus. It looks as if the moon has literally come apart and came back together, it has canyons, grooves, and all sorts of odd terrain. It is also elongated due to Uranus's tidal forces on it.
Ariel - (moon) at 720 miles across, it is a moon of Uranus with canyons in various places.
Umbriel - (moon) at 727 miles across, it is a dark cratered moon of Uranus.
Titania - (moon) at 981 miles across, it is a brownish speckled moon of Uranus.
Oberon - (moon) at 946 miles across, it is a brownish speckled moon of Uranus. It also has a mountain on its surface.
Neptune - (planet) at 30778 miles across, it is a blue ice giant with a thick atmosphere. Neptune sometimes has hurricane like blue spots. It has a few thin rings and ring arcs. Neptune has 13 satellites, of which only one (Triton) is a world.
Triton - (moon) at 1678 miles across, it is a pinkish-tan moon of Neptune, with geysers all over, it has a thin nitrogen atmosphere. Triton is cyrogenically cold at 35 degrees Kelvin
This region has several world sized objects, the most notable are Eris, Pluto and Charon, 2005 FY9, 2003 EL61, Orcus, and Quaoar. Most objects in this region are icy ACOs and various comets (also ACOs) and the satellites of other KBOs. Some objects out here are clearly worlds, but there are several others that are border line cases (they may be worlds or ACOs) and there's not enough info on them to sort it out. However according to this PDF from www.sc.eso.org, a few more worlds can be added (Varuna, Ixion, Huya, 1996 TL66, 2002 AW197, and 2002 TX300).
Orcus - (undeclared dwarf planet) at around 700 miles across, it is a dark world with a Pluto-like orbit. It has one satellite. It is one of the largest KBOs. I would give this object a 98% chance of being a world.
Pluto - (dwarf planet) at 1413 miles across, it is a pinkish-yellow world with darker regions. It has a faint methane atmosphere which freezes when Pluto gets further from the sun. It has three satellites of which one (Charon) is a world. Pluto was considered a planet for 75 years until Aug 2006 due to the IAU decision. In 1989, I had a dream where I seen Pluto and Charon (which I believe was an answer to a prayer of mine). During that time I assumed Pluto was a dark bluish-grey cratered world and Charon looked about the same, but in the dream it looked surprisingly a lot like the artist renderings do today - pinkish-yellow with a darker region facing Charon.
Charon - (moon) at 728 miles across, it is a greyish moon of Pluto - it and Pluto keep the same face towards each other as they orbit. In the previously mentioned dream, Charon was greyish and darker than Pluto with a slightly lighter hemisphere facing Pluto, it also had a mountain which faced Pluto which was a guyser that shot its material in a thin stream all the way to Pluto's surface - We'll need to wait for New Horizons to get there in 2015 to see if this turns out to be the case or not. If it is, it will be stunning surprise for planetary scientist, as well as myself.
Ixion - (potential dwarf planet) at about 500 miles, it is a moderately large KBO. It is dark red colored and appears to be a world occording to the PDF, (I'll give it a 90% chance).
Huya - (potential dwarf planet) at about 350 miles, it is a moderate sized KBO. It appears to be a world occording to the PDF (a very small one that is), (I'll give it an 80% chance).
Varuna - (undeclared dwarf planet) is about 600 miles across, it is believed to be slightly flattened due to its rotation. It has a somewhat reddish color and appears to be a world (I'll give it a 90% chance).
2002 TX300 - (potential dwarf planet) is less than 550 miles across and has a greyish color. According to the PDF, it is a world. I'll give it an 85% chance.
Haumea - (dwarf planet) is about 1400 miles by 800 miles by 575 miles. It has a strange capsule shape due to its rapid rotation. It has a bright greyish white color and its surface is mainly ice, inside it is likely made of rock. It's mass is a third of Pluto's. It was for three years known as 2003 EL61. It has 2 satellites and has also been called "Santa".
Quaoar - (undeclared dwarf planet) at about 780 miles across, it is a dark colored world with a nearly circular orbit. It is a notably large KBO. According to the IAU definition, it is very likely a dwarf planet (I'll give it aleast a 99% chance). It has a satellite.
Makemake - (dwarf planet) at about 1000 miles across, it is a very significant KBO and has finally been classified as a dwarf planet and given a real name. It is a pinkish Pluto-like world with frozen methane on its surface. It has been nicknamed "Easterbunny" and was previously known as 2005 FY9. Due to the long three year wait for it to get named, I drew this cartoon to reflect it. (drawn before it got named).
2002 AW197 - (potential dwarf planet) is about 430 miles across, according to the PDF, it is a world. (I'll give it an 80% chance.)
2007 OR10 - (potential dwarf planet) is about 700 miles across and was just announced. (I'll give it an 95% chance.)
Eris - (dwarf planet) is about 1490 miles across and is a bright white colored world with very little surface variations. It has one satellite. It was once referred to as "the tenth planet" and called "Xena", it is larger than Pluto and is the most notable of the worlds in this region.
1996 TL66 - (potential dwarf planet) is about 400 miles across, according to the PDF, it is a world. (I'll give it an 80% chance.)
The following may or may not be worlds, they are closer to the border line:
1999 TC36 - is about 300 miles across, I'll give it a 60% chance of being a world.
2001 QF298 - is about 350 miles across, I'll give it a 60% chance of being a world.
2003 AZ84 - is about 430 miles across, I'll give it a 70% chance of being a world.
1995 SM55 - (ACO) is about 300 miles across, according to the PDF mentioned above, this one is not a world.
2002 MS4 - is about 450 miles across, I'll give it a 40% chance.
2004 GV9 - is about 430 miles across, I'll give it a 40% chance.
2002 UX25 - (large ACO) is about 560 miles across and is quite reddish, it also has a satellite. According to the PDF, this one is not a world.
2001 UR163 - is about 430 miles across, I'll give it a 70% chance of being a world.
2002 TC302 - is less than 750 miles across (size unknown) - if it is around 750, it would likely be a dwarf planet, but its size is more likely around 500 miles or less. Very little info on this object is available. I'll give it a 50% chance.
1999 DE9 - is about 350 miles across, I'll give it a 60% chance of being a world.
2004 XR190 - AKA "Buffy" is in the 300-400 mile vacinity. It has a very circular orbit which is highly inclined. It is unknown if Buffy is a world or not, Ill give it a 40% chance.
This region as well as the next one the Oort cloud region haven't been searched out yet, very few objects have been found in this region, and only one world is known and that one is Sedna. As more is known about this region, more worlds will likely be found.
Sedna - (undeclared dwarf planet) at about 1000 miles across, it is a significant object in this vacinity (unless scores of Sedna sized objects are found here in the future) - so it very likely a dwarf planet (I'll give it a 99.99% chance). It has a highly eccentric orbit, bringing it to within Eris's orbit and taking it way out to about 900 AUs. It is dark red in color.