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Planetary classification

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Planetary classification is a scheme for classifying planets according to mass, surface, and composition.

It is estimated that there are 820 billion planets in the Milky Way Galaxy orbiting 180 billion stars, corresponding to the average of 4.55 planets per star. Based on the probability of being shut out in baseball scoring 4.55 runs per game, 95% of all stars would have planets. There are 1071 planets identified as of February 8, 2014, which is more than a billionth of all planets in our galaxy. There are 843 probable-clouded planets (787‰) and 228 probable terrestrial planets (213‰). There are ~524 billion terrestrial planets (639‰) and ~296 billion giant planets (361‰) in the Milky Way Galaxy.

Classifications Edit

Mass Edit

Planetary mass classification is the classification of planets by mass. The mass ranges from 1 Lunar mass to 13 Jupiter masses. This classification uses the letter codes in order of decreasing mass. There are three broad types of planets by mass: Jupiter-mass planet (class J), Neptune-mass planet (class N), and Earth-mass planet (class E) with subclasses a (super-), b (mid-) and c (sub-) in order of decreasing mass.

Planets are non-stellar objects that revolve around stars including the Sun that have suitable mass range that clear the neighborhoods without fusing deuterium in their cores. Brown dwarf (hyperjovian) and dwarf planet (hypoterrestrial) were originally included. It was removed because these are not planets. Brown dwarf is not considered a planet because they are massive enough to fuse deuterium in their core, somewhat like stars, and dwarf planet because it is not massive enough to clear the neighborhood.

Of all known planets, super-Jupiters are most abundant despite it is the rarest mass class of planet in the galaxy due to the fact that super-Jupiters are most easily detected with mid-Jupiters not far behind. Sub-Jupiters, midplanets, and super-Earth each have percentage in the teens. There are only few known mid-Earths and sub-Earths due to difficulties in detecting them, at just 5% of all known planets combined. Mid-Earth is the Milky Way's most abundant mass class of planet with sub-Earth close behind. Planets massing less than 20 M make up about 73% of all planets with remainder 27% are more massive than 20 M. For identified planets, however, the percentages are switched between these mass classes: 72% are over 20 M while 28% are under.

Class Symbol Name Mass range Composition Known planets Abundance in our galaxy
I Ja Super-Jupiter 2–13 MJ Gaseous 294 ~46 billion
II Jb Mid-Jupiter 0.5–2 MJ Gaseous 283 ~69 billion
III Jc Sub-Jupiter 0.1–0.5 MJ Gaseous or icy 121 ~65 billion
IV N Midplanet 0.03–0.1 MJ
10–32 M
Icy, watery, gaseous or rocky 145 ~123 billion
V Ea Super-Earth 2–10 M Rocky, watery, icy or gaseous 141 ~155 billion
VI Eb Mid-Earth 0.5–2 M Rocky, watery or icy 30 ~185 billion
VII Ec Sub-Earth 0.01–0.5 M Rocky 21 ~177 billion

Orbit Edit

Planetary orbit classification is the planet classification according to their orbital distance (semimajor axis) from the parent star.

Class Symbol Name Orbit range (AU) Known planets Abundance in our galaxy
I B Bellerophian <0.1 405 ~42 billion
II V Vulcanian 0.1–0.25 164 ~54 billion
III H Hermian 0.25–0.5 75 ~67 billion
IV C Cytherean 0.5–0.8 58 ~82 billion
V G Gaian 0.8–1.25 89 ~81 billion
VI M Martian 1.25–2.5 133 ~124 billion
VII A Alphian 2.5–5 89 ~135 billion
VIII J Jovian 5–10 36 ~105 billion
IX U Uranian 10–25 7 ~76 billion
X P Plutonian 25–50 6 ~29 billion
XI E Eridian 50–100 2 ~11 billion
XII S Sednian >100 7 ~13 billion

Surface Edit

Planetary surface classification is the classification of planets about what's on the surface, such as deserts, forests, and oceans. More than one surface class can be identified for one planet.

Class Name Symbol Life-bearing status Color Probable planets Abundance in our galaxy
0 Gas G Poor Various 843 ~296 billion
I Lava L Poor Red, orange 91 ~133 billion
II Crater Ct Poor Various 7 ~169 billion
III Barren B Fair Brown, gray 38 ~233 billion
IV Desert D Fair Tan, brown, peach, yellow 26 ~141 billion
V Mountain Mt Fair Brown, gray 5 ~23 billion
VI Ice I Good White, gray 4 ~113 billion
VII Ocean O Good Blue 63 ~52 billion
VII Forest F Excellent Green 0 ~620 million
IX City U Excellent Gray 0 ~16 million

Composition Edit

This scheme is about what the planet is dominantly made of, such as carbon, methane, or water. Like the surface classification, more than one composition class can be identified for one planet, albeit more rarely.

Class Name Symbol Life-bearing status Color Probable planets Abundance in our galaxy
0A Hydrogen H Poor Various 843 ~296 billion
0B Helium He Poor Various 0 ~301 million
I Iron Fe Poor Reddish brown ~2 ~9 billion
II Chlorine Cl Fair Green ~0 ~3 million
III Ammonia A Fair Brown ~0 ~24 billion
IV Phosphorus P Fair White ~1 ~427 million
V Methane M Fair Turquoise ~0 ~43 billion
VI Sulfur S Good Yellow ~4 ~13 billion
VII Carbon C Good Brown, black, gray ~6 ~86 billion
VIII Silicon Si Good Various 154 ~429 billion
IX Water W Excellent Blue ~61 ~77 billion

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