I have developed a system of classifying planetary bodies, including planets, dwarf planets, asteroids, satellites, and perhaps even some stars, that I feel is more versatile than the current classification system in effect. In the current scheme of astronomy, planets are usually divided into two major groups: the Terrestrial Planets (Mercury, Venus, Earth, Mars), and the Gas Giants (Jupiter, Saturn, Uranus, Neptune).
One of my problems with this scheme is that it is too general. Dividing all 8 planets in our Solar System (and presumeably extrasolar planets as well) into two groups leaves a lot of information out of the picture. It doesn't well reflect the special physical properties that each planet has due to differences in their anatomies. The internal dynamics of planets should be taken into consideration.
Another problem that I have with this system is its potential inaccuracy. For example, the label "Gas Giant" seems to be a misnomer to me. In reference to what I've learned, these planets are mostly liquid. According to my calculations, Jupiter is over 99% liquid by volume and Saturn is more than 95% liquid. Therefore, I think we should be calling them "Liquid Giants" if anything.
My new system of classification is based on the phases of matter present in these planets, and the order in which they are layered. Such layers are known in common terminology as the atmosphere (gas), the oceans and seas (liquid), the crust (solid), the mantle (liquid), and the core (solid or liquid). The presence or absence of such features in a planet contributes strongly to its behavior and physical attributes. This is what I call a "layering code".
For example, let's take the layering code of the Earth: GLSLS. Each letter in the code denotes a phase of matter; G for gas, L for liquid, and S for solid. The code starts with the outermost layer of the planet and moves inward. The G represents the outermost layer of the Earth: the atmosphere. The first L represents the liquid water that rests on top of the crust in seas and oceans. The first S represents the solid crust below the oceans. The second L represents the molten rock and metal in the mantle and outer core. Finally, the second S represents the innermost layer of Earth: the solid iron-nickel core.
My classification system groups planetoids based on "phaseotype", which is a two-part code that is assigned to a planet based on its layering code. Phaseotypes have two components, a number and a letter. Here is a list of what each number and letter denotes in a phaseotype:
I - These planetoids do not possess a significant atmosphere or hydrographics.
II - These planetoids possess a significant atmosphere, but no hydrographics.
III - These planetoids possess a significant atmosphere and hydrographics.
a - These planetoids have bodies that, except for hydrographics, are uniformly solid.
b - These planetoids have solid crusts, and a molten mantle, but no solid core.
c - These planetoids have solid crusts, a molten mantle, and a solid core.
d - These planetoids do not have any solid body.In accordance with my classification system, a "significant" atmosphere is an atmosphere with a surface pressure of over 1 pascal. A "tenuous", or "insignificant" atmosphere has a pressure of 1 pascal or less. There isn't any "magical" difference between atmospheres that arises at this pressure, but I use it as an arbitrary cut-off point.
By mixing and matching numbers and letters, you come up with the different phaseotypes that are included in my classification system.
The following is a list of the different phaseotypes of planets that make up this scheme; including layering codes, descriptions, and properties of each phaseotype. Although I also try to mention real-life examples of these phaseotypes in some places, it is sometimes difficult because of our limited understanding of planetary structure. Different people think different planets have different internal structures. A fuller knowledge of this is required for my phaseotypic classification system to be effective.
Phaseotype Ia
Layering Code S Phaseotype Ia planetoids have one of the simplest of all structures. They are composed completely of solid matter. Although they may have distinct layers made of different materials (such as a rocky crust and an iron core), each layer is in the solid phase. Planetoids of this type can be considered as having few internal dynamics, and have little to no self-induced tectonic activity. Any sort of seismic phenomena such as tremors are more likely to be generated by gravitational stress from nearby planetoids or stellar bodies than from interior movement.
Phaseotype Ia planetoids have a tenuous or nonexistant atmosphere, which means that weather is not present on them or is present only faintly. Wind erosion and nonvolcanic clouds may be absent in their environment. With a tenuous atmosphere, the surface temperature of Phaseotype Ia planetoids varies much more from day to night than with planetoids that have significant atmospheres.
Many planetoids of this type can be expected to be small. Due to their dimunitive size, their internal pressure is insufficient to melt their interior. Their gravity is also too weak to hold onto any concernable atmosphere. This weak gravity means that many of them are oblong or nonspherical, unlike most other types.
A very large number of asteroids will likely be identified as Phaseotype Ia planetoids. Small satellites should also be enlisted as Phaseotype Ia's. The asteroids Vesta and Ceres are probably this type of planetoid. Pluto may also belong to this group.
Phaseotype Ib
Layering Code SL These planetoids are expectedly larger than most in the Phaseotype Ia group. Due to their larger size, their internal pressure is sufficient to melt their solid interior, producing a "mantle" of what may usually be molten rock or metal. Because they have a layer of fluid beneath their crust, tectonic activity will be far more pronounced in Phaseotype Ib planetoids than in Phaseotype Ia, as convection currents flow through the mantle. Such land features as mountains and chasms should be far more prominent in Phaseotype Ib's than Phaseotype Ia's as well.
As with Phaseotype Ia planetoids, these objects lack a significant atmosphere. Again, this means little or no weather. If a planetoid has enough mass to melt its center, then it may well have enough gravity to attract an atmosphere. Because of this, You should expect to find Type Ib planetoids in gasless or low-gas regions of space, probably far away from stars. However, being close to a star might also strip a planetoid of most of its atmosphere, due to solar wind. This may be the reason that Mercury has a thin atmosphere. Mercury is probably a Phaseotype Ia planetoid.
Phaseotype Ic
Layering Code SLS If a moderately-sized planetoid has enough mass, it can melt its interior. However, there may still be a kernel of solid matter left at the center of the planetoid, called the core. This is the case with Type Ic planetoids. Because the temperature inside the planet is sufficient to turn the mantle into liquid, we should expect the core to be made of different material than the mantle. Usually, the core will be composed of metals such as iron and nickel.
The tectonic movement in Phaseotype Ic planetoids can be comparable to Phaseotype Ib planetoids. This is due, of course, to the molten rock they possess under their crust. What effect a solid core would have on such activity, I do not know. I wouldn't expect it to be too great, unless the core is very large relative to the entire planetoid.
Their asphyxiating surfaces are like that of the previous two types. They should be found in similar areas of space that Phaseotype Ib's exist, so that their gravity cannot gather a significant atmosphere. Of course, solar wind might also blow an atmosphere away. One example of a Phaseotype Ic body is the Earth's own Moon, which has a very thin atmosphere. Pluto could be in this group, if its internal warmth is sufficient to melt subsurface ices.
Phaseotype IIa
Layering Code GS Anatomically, this type of planetoid is identical to those in the Phaseotype Ia group. What sets them apart is their atmosphere. This feature creates a more uniform climate than airless worlds have. Wind erosion and clouds are still unlikely, because the atmosphere will be thin and devoid of moisture.
This planetoid type is a bit of a balancing act. It has to be small enough to retain a solid interior, but large enough to hold an atmosphere. This may not even be possible. If the planetoid is composed mostly of dense metal, then it may be able to hold a stable atmosphere on its own. I would expect these types to have a relatively thin atmosphere at best when compared to Earth.
Phaseotype IIb
Layering Code GSL This is an airy analogy of the Phaseotype Ib planetoid. They can be expected to have thicker atmospheres than Phaseotype IIa's, since they would typically have more gravity. Under these circumstances, wind erosion could become an important factor. Clouds would be rare to nonexistant, because of the lack of moisture.
One might expect these planetoids to be relatively common, since they can exist in many sizes and would not be difficult to form. Mars is an example of this planetoid type.
Phaseotype IIc
Layering Code GSLS Similar to the Phaseotype Ic planetoid, this type has a solid core. It also possesses an atmosphere, and could be expected to have properties analogous to Phaseotype IIb planetoids, including wind erosion, and tectonic movement. They should also be common, maybe even more common than Phaseotype IIb's are. Venus should be a Phaseotype IIb planetoid, assuming that it has a dry surface devoid of sulfuric acid seas or lava lakes.
Phaseotype IId
Layering Code G Along with the Phaseotype Ia planetoids, this type has among the simplest of structures. It is composed completely of gas, almost like an atmosphere in and of itself. The gas is least dense and coldest around the edge of the planetoid, and is the most dense and hottest at the center.
This is somewhat of a speculative phaseotype, since I don't normally think of gases gathering together into a planet-like body without producing some sort of liquid or solid center due to pressure. This phaseotype would also be a balancing act; large enough to hold itself together with gravity, but small enough to prevent condensation at its core. This may not be possible in a conventional sense.
Actually, many stars could be effectively classified as Phaseotype IId planetoids, since they are completely gaseous. They are, however, different from planets because of the fusion reactions that occur in their core. The heat liberated in these reactions is sufficient to prevent the gas from condensing into a liquid or solid state.
Phaseotype IIIa
Layering Code GLS This is the first of the planetoid types that possesses hydrographics. Hydrographics are liquid reserviors on a planet's surface, such as seas, lakes, oceans or rivers. Though these hydrographics may be composed of water, they may also be made of other liquids, such as liquified ammonia, liquid hydrogen, molten sulfur, or hydrocarbons.
Since liquids cannot exist in a vacuum, all Phaseotype IIIa planetoids have atmospheres. Without the ambient pressure of an atmosphere, hydrographics would boil away. The hydrographics of a world may or may not cover the entire surface of that planetoid. The hydrographics are always present above the crust, however. Due to evaporation, Phaseotype IIIa planetoids have dynamic weather patterns, including cloud formation and precipitation.
Phaseotype IIIa planetoids are like Phaseotype IIa planetoids with hydrographics. However, this does not necessarily mean that they are made mostly of rock. Imagine a hypothetical planet made entirely of water. The atmosphere is pure water vapor, the hydrographics cover the entire surface of the planetoid and form a deep ocean. This ocean is so large that the internal pressure at deep levels causes the water to revert to ice. This is not typical ice, however, as it is denser than the ice we normally know of. It makes up the entire core of the planet. Phaseotype IIIa planetoids of this form may be very large. If the "Gas Giants" have solid cores, then this is the type they would be.
Phaseotype IIIb
Layering Code GLSL This type is like Phaseotype IIb planetoids with hydrographics. Dynamic weather patterns could be expected here as well. However, tectonic activity coupled with an ocean of liquid may produce phenomena similar to tsunami waves.
Phaseotype IIIc
Layering Code GLSLS This is the most complex of all planetoid types. Starting from the outside, it is surrounded by an atmosphere, below which is an ocean of liquid. Below this ocean is a solid crust, then a liquid mantle, and finally a solid core. This is in essence a Phaseotype IIc planetoid with hydrographics. The Earth is this type of planetoid. Titan may also belong in this group, if its internal heat is sufficient.
Phaseotype IIId
Layering Code GL This world is made entirely out of fluids. It has a body made of liquid, perhaps liquid hydrogen or molten rock, and a thick, active atmosphere. Planets of this type may be very large. All four of the "Gas Giants" of the Solar System may well fall into this group. The Gas Giants are thought to have a thick atmosphere of hydrogen and helium, an ocean of liquid hydrogen beneath that, a layer of liquid metallic hydrogen even further down, and a core of molten rock at their center. Some, however, believe the Gas Giants to have solid cores, which would classify them as Phaseotype IIIa planetoids.
The presence of metallized hydrogen fluid allows for the creation of tremendous magnetic fields, which may be a characteristic common to many Phaseotype IIId planetoids. One might even go so far to say that "Brown Dwarf" stars fit into this class, which are between stars and planets in size.
