------------------------------------------- DEFINING AND CLASSIFYING A PLANET (of one sort or another) Characteristics, Circumstances, Cosmogony ------------------------------------------- I. Is it a planet? A. Planet or brown dwarf? Two possible tests based on characteristics. 1. Brown dwarf as fusor of deuterium (~13 JM). 2. Brown dwarf as fully convective (Wiki ~10 JM?). B. Lower limit in size? 1. If meteoroids included as "nanoplanets," then 100 microns - 10 meters or larger. 2. If "minor planets" are lower limit, then about 10-100 meters. II. What kind of planet? A. General Circumstances. 1. Zeroeth Level Planet -- free-floating. Orbits neither fusor nor larger nonfusor. 2. Primary Planet -- orbits a fusor, and not a larger nonfusor. 3. Secondary Planet or Satellite, orbits a larger nonfusor, with both often orbiting a fusor -- but maybe sometimes not. B. For Primary or Secondary Planet, Dynamical Status and Hydrostatic Equilibrium. (see Table). 1. Dominant or Belt Planet/Satellite? 2. Macroplanet, Mesoplanet, or Microplanet? C. Is Cosmogony Destiny? Origins and Circumstances. 1. Three main levels of origins. A. Zeroeth Level Origins: Core of collapsed region in molecular cloud, "starlike," subbrown dwarf planet if remains nonfusor. B. First Level Origins: Formation from circumstellar or protoplanetary disk -- might apply to some brown dwarfs as well as planets. C. Second Level Origins: Formation near accretion disk for planet, or possibly by collision (Theia hypothesis of "Big Smack" for Earth-Moon system). 2. How circumstances might change -- some examples. A. Ejected planet: first-level origins in protoplanetary disk, but "cleared out of neighborhood" later, and now zeroeth-level planet. B. Immigrant planet? Might sub-brown dwarf planet formed from central core collapse of molecular cloud, with zeroeth-level origins, be captured by gravitation of fusor it encounters and "naturalized" into solar system, now primary planet? C. Escaped moon. Satellite somehow diverted from planet it's orbiting, now primary planet. (At one time proposed for 134340 Pluto as former moon of Neptune.) D. Primary planet captured as moon. This has been proposed for Martian satellites Deimos and Phobos: primary planet (here more specifically microplanet) might form independently (e.g. in Main Asteroid Belt), then have encounter with larger planet and become satellite or secondary planet.