{"id":16222,"date":"2022-08-15T00:00:00","date_gmt":"2022-08-14T22:00:00","guid":{"rendered":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/?post_type=purple_issue&p=16222"},"modified":"2022-08-22T11:40:06","modified_gmt":"2022-08-22T09:40:06","slug":"if-the-moon-were-bigger-at-what-point-would-it-be-deemed-a-planet-and-the-earth-and-moon-a-binary-planet-system","status":"publish","type":"post","link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/2022\/08\/15\/if-the-moon-were-bigger-at-what-point-would-it-be-deemed-a-planet-and-the-earth-and-moon-a-binary-planet-system\/","title":{"rendered":"If the Moon were bigger, at what point would it be deemed a planet and the Earth and \u2018Moon\u2019 a \u2018binary planet\u2019 system?"},"content":{"rendered":"\n

If the Moon were bigger, at what point would it be deemed a planet and the Earth and \u2018Moon\u2019 a \u2018binary planet\u2019 system?<\/h3>\n\n

DERRYCK MORTON, POUGHILL, DEVON <\/p>\n\n

\"\"<\/figure><\/div>\n\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. <\/p>\n\n

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

Other criteria have been suggested, such as the position of the \u2018barycentre\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. 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. AGu<\/strong><\/em><\/p>\n\n

<\/div>
\n

Email your questions to<\/span>
questions@sciencefocus.com<\/a>
or submit on Twitter<\/span>
@sciencefocus<\/a><\/p>\n<\/div><\/section>\n\n

IMAGE: GETTY IMAGES<\/p>\n","protected":false},"excerpt":{"rendered":"

If the Moon were bigger, at what point would it be deemed a planet and the Earth and \u2018Moon\u2019 a \u2018binary planet\u2019 system? DERRYCK MORTON, POUGHILL, DEVON 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 […]<\/p>\n","protected":false},"author":24,"featured_media":16565,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"ub_ctt_via":"","purple_page_number":"82","purple_custom_meta_purple_page_number":"82","purple_seq_number":"2","purple_custom_meta_purple_seq_number":"2","purple_source_article":"article_82-2.xml","purple_custom_meta_purple_source_article":"article_82-2.xml","purple_source_issue":"August-2022","purple_custom_meta_purple_source_issue":"August-2022","purple_external_id":"August-2022-82-2","purple_custom_meta_purple_external_id":"August-2022-82-2","purple_issue_code":"|0000089657||","purple_custom_meta_purple_issue_code":"|0000089657||","purple_android_product":"com.focus.magazine.issue381","purple_custom_meta_purple_android_product":"com.focus.magazine.issue381","purple_ios_product":"com.focus.magazine.issue381","purple_custom_meta_purple_ios_product":"com.focus.magazine.issue381","purple_web_product":"","purple_custom_meta_purple_web_product":"","purple_publication_id":"0f422ad1-c939-476d-9f82-a410052ad4c3","purple_migrated":"","kt_blocks_editor_width":"","apple_news_api_created_at":"2022-08-15T15:42:18Z","apple_news_article-theme":"","apple_news_api_id":"1786ea87-84a0-4167-a13a-419130ded405","apple_news_api_modified_at":"2022-08-22T09:40:13Z","apple_news_api_revision":"AAAAAAAAAAAAAAAAAAAACA==","apple_news_api_share_url":"https:\/\/apple.news\/AF4bqh4SgQWehOkGRMN7UBQ","apple_news_coverimage":0,"apple_news_coverimage_caption":"","apple_news_is_hidden":false,"apple_news_is_paid":true,"apple_news_is_preview":true,"apple_news_is_sponsored":false,"apple_news_maturity_rating":"","apple_news_pullquote":"","apple_news_pullquote_position":"","apple_news_article_theme":"","apple_news_sections":"[]"},"categories":[30],"tags":[15],"apple_news_notices":[],"featured_image_src":"https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644.jpg","author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/author\/importmanagerhubsprylab-com\/"},"acf":{"readingTimeMinutes":"2","apple_news_title":""},"uagb_featured_image_src":{"full":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644.jpg",1200,800,false],"thumbnail":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644-150x150.jpg",150,150,true],"medium":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644-300x200.jpg",300,200,true],"medium_large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644-768x512.jpg",768,512,true],"large":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644-1024x683.jpg",800,534,true],"1536x1536":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644.jpg",1200,800,false],"2048x2048":["https:\/\/c01.purpledshub.com\/uploads\/sites\/42\/2022\/08\/GettyImages_1057166644.jpg",1200,800,false]},"uagb_author_info":{"display_name":"importmanagerhub@sprylab.com","author_link":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/author\/importmanagerhubsprylab-com\/"},"uagb_comment_info":0,"uagb_excerpt":"If the Moon were bigger, at what point would it be deemed a planet and the Earth and \u2018Moon\u2019 a \u2018binary planet\u2019 system? DERRYCK MORTON, POUGHILL, DEVON 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…","_links":{"self":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts\/16222"}],"collection":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/users\/24"}],"replies":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/comments?post=16222"}],"version-history":[{"count":9,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts\/16222\/revisions"}],"predecessor-version":[{"id":16909,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/posts\/16222\/revisions\/16909"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media\/16565"}],"wp:attachment":[{"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/media?parent=16222"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/categories?post=16222"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c01.purpledshub.com\/bbcsciencefocus\/wp-json\/wp\/v2\/tags?post=16222"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}