Search the Community

With the huge variety of planets being discovered now, scientists have been theorizing about other types of planets. Some have real-life examples (like Chthonian Planets) while others are just science fiction for now (Coreless Planets). I also have a lot of hypothetical planet types. Some of these types have examples in our own solar system, which goes to show how exotic our planetary neighborhood really is. This list will be constantly updated, and other types for other forum users are welcome! OCEANIAS: These are the so-called "Water worlds" that have been appearing in science fiction for years. However, not all oceanias fit into one category. Water planets fall into 3 groups: Water Dwarfs, Classical Oceanias, and Water Giants. All 3 groups are defined by radius, mass, and proportion of water. WATER DWARFS: Tiny ocean worlds are known as Water Dwarfs. These wet midgets range from 0.05-0.5 Earth Radii and 0.01-0.4 Earth Masses, and are more commonly moons than planets. They form from small ice worlds, with radii at most 0.5 ER, migrating inwards either alone or around a migrating gas giant. Water Dwarfs could also be around gas giants farther away from the habitable zone of their stars. They are either heated by tidal forces, greenhouse gases, or both. Unlike moons like Europa and Enceladus, Water Dwarfs do not have ice crusts if they're outside the habitable zone. Those would still be classified as ice worlds. There are no known examples of Water Dwarfs yet, but some gas giants like Kepler-458b may have some as moons. If Laythe from KSP did not have any islands, then it would be a Water Dwarfs. CLASSICAL OCEANIAS: These are ocean worlds that are more or less similar in size and mass to Earth and other sci-fi ocean planets, like Kamino. Classical Oceanias cannot be more than 50% smaller or larger than Earth. Otherwise, they are either Water Dwarfs or Giants. They range from 0.5-1.5 Earth Radii and 0.4-1.25 Earth Masses. However, COs cannot have a density greater than 2.5 grams/cubic cm or gravity greater than 0.85 gees. That would make them Mini Earths or regular terrestrial planets. COs form in the same ways as Water Dwarfs, and have no known examples. But these objects could form around gas giants like HD 125612 b. WATER GIANTS: The final type of ocean planet is much more different than the other two classes, yet seems to be much more common. Water Giants are similar in size and mass to gas dwarfs and ice giants, but at least 70% of their mass is liquid water. The remaining mass is a rocky outer core, an iron inner core, and a relatively thin atmosphere. Only 1-3% of a Water Giant's mass is its atmosphere. That's really thin compared to those of Neptune and Jupiter. However, certain specifications need to be put into place for a plane to be called a Water Giant. They range from 3-5 Earth Radii and 6-20 Earth Masses, but some radius-mass ratios within these ranges can turn Water Giants into Ice Giants. Take Gliese 436 b for example. It has 4.3 times the radius of Earth, putting it right in the range. But the mass of 22 Earth Masses gives it a gravity 18% higher than that on our own planet. This compresses the water into ice and removes the planet from the Water Giant category. WGs form from ice giants or gas dwarfs with high levels of H2O inside them that migrate close to their parent stars. Hydrodynamic escape can reduce the planet's atmosphere to the mass of what other WGs have. They can also form from large ice worlds melting and/or sublimating. There are several examples, such as GJ 1214 b and Kepler-22b.