{"id":18943,"date":"2022-10-22T19:00:22","date_gmt":"2022-10-22T17:00:22","guid":{"rendered":"https:\/\/www.sciencefocus.com\/?p=128631"},"modified":"2022-10-22T19:21:10","modified_gmt":"2022-10-22T17:21:10","slug":"what-is-a-binary-planet-system","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/rss_feed\/what-is-a-binary-planet-system\/","title":{"rendered":"What is a binary planet system?"},"content":{"rendered":"

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By Dr Alastair Gunn\n \t\t<\/p>

Published: Saturday, 22 October 2022 at 12:00 am<\/p>

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A binary planet system is a theorised arrangement where the mass of two closely orbiting objects, are similar.<\/p>\n

The criteria which distinguish between a \u2018binary planet\u2019 (or \u2018double planet\u2019) and a \u2018planet-moon system\u2019 (or \u2018planet-satellite system\u2019) are, unfortunately, not well defined. An obvious criterion is the ratio of the two objects\u2019 masses. A value close to 1 implies the objects are very similar in mass, but how close to 1 does the ratio have to be for the system to be a double planet rather than a planet and moon?<\/p>\n

The Earth-Moon system has a ratio of only 0.01230, while the Pluto-Charon system<\/a> has a ratio of 0.122. Neither is particularly close to 1, and so neither is regarded as a binary planet.<\/p>\n

Other criteria have been suggested, such as the position of the \u2018barycentre<\/a>\u2019 about which the two objects orbit, the strength of the gravitational force of the parent star on the pair, or how the objects were formed in the first place.<\/p>\n

The Pluto-Charon system could be described as a double planet because both objects orbit around a point above their surfaces. This is not true of the Earth-Moon system, as the barycentre is about 1,700km below Earth\u2019s surface. But this, and other definitions, are not wholly adequate \u2013 and none are fully adopted by astronomers.<\/p>\n

Read more:<\/strong><\/p>\n