sometimes a planet was named after its sun , followed by the number corresponding to the planet 's ordering in the stellar system ( like how we sometimes refer to earth as sol iii ) ; many times a planetparticularly if it is perhaps not quite a planet by conventional standardswould be named after one of its prominent or recurring features ; other times a planet might be named terra , followed by a sequence of digits , so as to convey that the planet is easily inhabitable and not some ferocious gas giant .