Double planet arguing that Jupiter is a double star is "not" analogous to arguing Pluto-Charon is a double dwarf planet. The problem is that Jupiter is not even a star, or even a brown dwarf, and due to its low mass it is unable to achieve any form of fusion. Isaac Asimov suggested a distinction between planet–moon and double-planet structures based in part on what he called a "tug-of-war" value, which does not consider their relative sizes. This quantity is simply the ratio of the force exerted on the smaller body by the larger (primary) body to the force exerted on the
Gas dwarf extrasolar planet that might be a gas dwarf is Kepler-138d, which is less massive than Earth but has a 60% larger volume and therefore has a density (2.1(+2.2/-1.2) grams per cubic centimetre) that indicates either a substantial water content or possibly a thick gas envelope. A low-mass gas planet can still have a radius resembling that of a gas giant if it has the right temperature. Gas dwarf A gas dwarf is a gas planet with a rocky core that has accumulated a thick envelope of hydrogen, helium, and other volatiles, having as result a total radius between 1.7 and