Editing Double planet (section)

=== Mass ratios closer to 1 ===

One important consideration for defining "double planets" is the ratio of the masses of the two bodies. A mass ratio of 1 would indicate bodies of equal mass, and bodies with mass ratios closer to 1 are more attractive to label as "doubles".{{citation needed|date=May 2023}} Using this definition, the satellites of Mars, Jupiter, Saturn, Uranus, and Neptune can all easily be excluded; they all have masses less than 0.00025 ({{frac|4000}}) of the planets around which they revolve. Some [[dwarf planet]]s, too, have satellites substantially less massive than the dwarf planets themselves.

The most notable exception is the Pluto–Charon system. The Charon-to-Pluto mass ratio of 0.122 (≈ {{frac|1|8}}) is close enough to 1 that Pluto and Charon have frequently been described by many scientists as "double dwarf planets" ("double planets" prior to the 2006 definition of "planet"). The [[International Astronomical Union]] (IAU) earlier classified Charon as a satellite of Pluto, but had also explicitly expressed the willingness to reconsider the bodies as double dwarf planets in the future.<ref>{{Cite web|title=International Astronomical Union {{!}} IAU|url=https://www.iau.org/public/themes/pluto/|access-date=2021-09-11|website=www.iau.org}}</ref> However, a 2006 IAU report classified Charon–Pluto as a double planet.<ref>{{Cite journal|title=The Public Communication Activities at the 2006 General Assembly (GA)|url=https://www.iau.org/static/public_press/iau_po_report.pdf |archive-url=https://web.archive.org/web/20130501174441/http://www.iau.org/static/public_press/iau_po_report.pdf |archive-date=2013-05-01 |url-status=live|journal=International Astronomical Union|pages=45}}</ref> 
[[File:ESO-L._Calçada_-_Eso1142c_(by).jpg|thumb|Artist's impression of the Eris-Dysnomia system]]
The Moon-to-Earth mass ratio of 0.01230 (≈ {{frac|81}}) is also notably close to 1 when compared to all other satellite-to-planet ratios. Consequently, some scientists view the Earth–Moon system as a double planet as well, though this is a minority view. [[Eris (dwarf planet)|Eris]]'s lone satellite, [[Dysnomia (moon)|Dysnomia]], has a radius somewhere around {{frac|1|4}} that of [[Eris (dwarf planet)|Eris]]; assuming similar densities (Dysnomia's compositional make-up may or may not differ substantially from Eris's), the mass ratio would be near {{frac|40}}, a value intermediate to the Moon–Earth and Charon–Pluto ratios.