{"id":632,"date":"2026-02-27T20:47:31","date_gmt":"2026-02-27T10:47:31","guid":{"rendered":"https:\/\/stevewatson.info\/blog\/?p=632"},"modified":"2026-02-27T20:47:31","modified_gmt":"2026-02-27T10:47:31","slug":"planetary-categorization","status":"publish","type":"post","link":"https:\/\/stevewatson.info\/blog\/2026\/02\/27\/planetary-categorization\/","title":{"rendered":"Planetary Categorization"},"content":{"rendered":"<p><span style=\"color: #000000;\">The explosion in exoplanet discoveries has revealed that the Solar System is very far from a typical stellar system, and a need has arisen for a categorization of planetary types that includes far more than the kinds of planets found orbiting the Sun. To form these classification appeal has been made to a range of characteristics that are at least observable. The principal such characteristics are<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">r = Radius (r<sub>E<\/sub>)<\/span><\/li>\n<li><span style=\"color: #000000;\">m = Mass (m<sub>E<\/sub>)<\/span><\/li>\n<li><span style=\"color: #000000;\">D = Density (x H<sub>2<\/sub>O)<\/span><\/li>\n<li><span style=\"color: #000000;\">T = Temperature (eq. to 1AU from Sun) \u2013 referring to the irradiation of the planet<\/span><\/li>\n<li><span style=\"color: #000000;\">a = Atmospheric composition (<em>n<\/em>)<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>n<\/em> = 0: No atmosphere (P &lt; 0.001b,)<\/span><\/li>\n<li><span style=\"color: #000000;\">else: <em>n<\/em> = mean molecular mass of atmospheric gases.<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<p><span style=\"color: #000000;\">Together with a few other observables these can be used to produce the following table of categorizations.<\/span><\/p>\n<ul>\n<li><span style=\"color: #000000;\">Common\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span>\n<ul>\n<li><span style=\"color: #000000;\">Orbital focus<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Rogue<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Not orbiting a star<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Circumbinary<\/em>\u00a0\u00a0\u00a0\u00a0 Orbiting a binary star<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Circumtriple<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Orbiting a triple star<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Orbital character<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Eccentric<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Highly eccentric orbit<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Double<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Two planets orbiting each other<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Trojan<\/em>\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Co-orbiting with another planet<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Solid\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0r &lt; 1.7\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 m &lt; 6\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0D \u2248 5<\/span>\n<ul>\n<li><span style=\"color: #000000;\">Structure<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Coreless<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 No metallic core, thus essentially all mantle<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Composition<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Carbon<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Iron core w\/ carbon-based mantle<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Iron<\/em> \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Iron core w\/ minimal mantle<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Ocean<\/em> (1)\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 Significant hydrosphere around core\/mantle\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Silicate<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Iron core w\/ silicone-based mantle<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">History<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Chthonian<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Close to star. Ex-fluid with envelope stripped away<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Surface<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Desert<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Dry desert (<em>Arid<\/em>, <em>Dune<\/em>)<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Hycean<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Ocean w\/ Hydrogen envelope<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Ice<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Frozen volatiles (eg. water, ammonia, methane)<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Lava<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 Lava<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Ocean<\/em> (2)\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0Liquid (usually H<sub>2<\/sub>O.) Oceans may be sub-surface<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Habitability<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Goldilocks<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 T \u2248 1<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Size<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Sub-Earth<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 r &lt; 0.8\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 m &lt; 0.5<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Earth<\/em>(-<em>sized<\/em>)\u00a0 \u00a0 \u00a0 \u00a00.8 &lt; r &lt; 1.7\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0.5 &lt; m &lt; 6<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Super-Earth<\/em>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a06 &lt; m &lt; 10<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Mega-Earth<\/em>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 10 &lt; m<\/span><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Fluid\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a01.7 &lt; r,\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a06 &lt; m\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 D &lt;&lt; 5 \u00a0<\/span>\n<ul>\n<li><span style=\"color: #000000;\">Irradiation<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Hot<\/em>&#8211;\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 T &gt;&gt; 1<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Cold-\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 <\/em>T &lt;&lt; 1<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Size<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Super-Earth<\/em> (<em>Gas Dwarf<\/em>)\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 6 &lt; m &lt; 10<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Mini-Neptune<\/em>\u00a0 \u00a0 \u00a01.7 &lt; r &lt; 3.9\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a06 &lt; m &lt; 20 (<em>sic<\/em>)\u00a0<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Sub-Neptune<\/em>\u00a0 \u00a0 \u00a0 \u00a01.7 &lt; r &lt; 3\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 m &lt; 10<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Neptunian<\/em>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 3 &lt; r &lt; 5 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 10 &lt; m &lt; 20<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Super-Puff<\/em>\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a04 &lt; r\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 m &lt; 4\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 D &lt; 0.8<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Super-Neptune<\/em>\u00a0 \u00a0 5 &lt; r &lt; 7 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 20 &lt; m &lt; 80<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Jovian<\/em> \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 7 &lt; r &lt; 10\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 80 &lt; m &lt; 400<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Puff planet<\/em> \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 80 &lt; m &lt; 400\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 D &lt; 0.8<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Super-Jupiter<\/em>\u00a0\u00a0\u00a0\u00a0 10 &lt; r \u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 400 &lt; m &lt; 4000<\/span><\/li>\n<\/ul>\n<\/li>\n<li><span style=\"color: #000000;\">Composition<\/span>\n<ul>\n<li><span style=\"color: #000000;\"><em>Gas Giant<\/em>\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 0 &lt; a &lt; 4<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Helium\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/em>a \u2248 4<\/span><\/li>\n<li><span style=\"color: #000000;\"><em>Ice Giant\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0\u00a0 <\/em>4 &lt; a<\/span><em><span style=\"color: #000000;\">\u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0 \u00a0<\/span> \u00a0 \u00a0 \u00a0 \u00a0\u00a0<\/em><\/li>\n<\/ul>\n<\/li>\n<\/ul>\n<\/li>\n<\/ul>\n","protected":false},"excerpt":{"rendered":"<p>The explosion in exoplanet discoveries has revealed that the Solar System is very far from a typical stellar system, and a need has arisen for a categorization of planetary types that includes far more than the kinds of planets found orbiting the Sun. To form these classification appeal has been made to a range of [&hellip;]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[54],"tags":[],"class_list":["post-632","post","type-post","status-publish","format-standard","hentry","category-space"],"_links":{"self":[{"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/posts\/632","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/comments?post=632"}],"version-history":[{"count":1,"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/posts\/632\/revisions"}],"predecessor-version":[{"id":633,"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/posts\/632\/revisions\/633"}],"wp:attachment":[{"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/media?parent=632"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/categories?post=632"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/stevewatson.info\/blog\/wp-json\/wp\/v2\/tags?post=632"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}