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Interactions between Earth\u2019s solid inner core, its molten outer core and its rocky mantle control how fast the planet rotates.Credit: Gregoire Cirade\/SPL<\/p>\n
Small fluctuations in the length of Earth\u2019s 24-hour day can be explained by a battle between forces generated by the movement of the planet\u2019s metallic core. The finding, reported today in Nature1<\/a>, suggests that geophysicists could be on the right track to understanding mysterious structures in Earth\u2019s deep interior<\/a>.<\/p>\n The planet\u2019s rate of rotation changes subtly over time<\/a>, giving rise to variations in the length of our day that are on the order of just a few milliseconds over decades. Geophysicists measure these changes by observing Earth\u2019s position relative to distant cosmic objects.<\/p>\n Researchers have suspected that these variations are linked to interactions between Earth\u2019s core and its rocky mantle, but it wasn\u2019t clear what forces were involved, says Mathieu Dumberry, a geophysicist at the University of Alberta in Edmonton, Canada. Scientists know that it is the core \u201cthat\u2019s responsible for these decadal changes. But how does it do it?\u201d he says. \u201cThis is the part that\u2019s unclear.\u201d<\/p>\n Core torque<\/p>\n Earth\u2019s core is a Mars-sized ball at the centre of the planet made up mostly of iron. The inner core is solid and can rotate independently within a molten, flowing outer core. There are a few ways researchers have proposed that these parts of the core can couple with the rocky mantle that surrounds them to either slow or accelerate the planet\u2019s overall rotation.<\/p>\n Has Earth\u2019s inner core stopped its strange spin?<\/p>\n <\/a><\/p>\n One is by creating mechanical torque, which is a twisting force: the flow of the molten outer core could push against bumps and bulges at its interface with the mantle, like a river flowing around rocks. Another possibility is that the magnetic field generated by the flow of the outer core attracts iron-rich parts of the mantle, generating electromagnetic torque. And a third force could come from gravity pulling dense regions of the inner core towards anomalously dense regions of the mantle.<\/p>\n Dumberry and his colleague Huifeng Zhang, also at the University of Alberta, developed a model to explore how different combinations of these forces would alter the length of Earth\u2019s day. A key part of this model relied on research published in 20232<\/a> that used seismic waves from earthquakes to measure the inner core\u2019s rate of rotation relative to the rest of the planet since the 1960s. The work found that the inner core spun slightly faster relative to the rest of the planet until around 2010<\/a>, when it began rotating more slowly.<\/p>\n Gravity always wins<\/p>\n The researchers found that their model best matched the record of changes in Earth\u2019s length of day when gravitational torque was the dominant force. But it had to be balanced by the electromagnetic and mechanical torques pushing in the opposite direction in a kind of geophysical tug-of-war. \u201cBefore we obtained the result, we didn\u2019t know they are competing with each other,\u201d Zhang says.<\/p>\n This push-and-pull battle also seems to influence the rate of rotation of the inner core. According to the model, the inner core \u2018wants to be aligned\u2019 with the mantle because its dense regions are attracted to the mantle\u2019s dense regions, Dumberry explains. But over time, it gets pulled out of alignment by the generally westward flows of the outer core, before being slowly pulled back eastward into position by gravity.<\/p>\n","protected":false},"excerpt":{"rendered":"Interactions between Earth\u2019s solid inner core, its molten outer core and its rocky mantle control how fast the…\n","protected":false},"author":2,"featured_media":858602,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[32],"tags":[19944,22174,1159,1160,16492,79],"class_list":["post-858601","post","type-post","status-publish","format-standard","has-post-thumbnail","category-science","tag-computer-science","tag-geophysics","tag-humanities-and-social-sciences","tag-multidisciplinary","tag-planetary-science","tag-science"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/858601","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/comments?post=858601"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/posts\/858601\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media\/858602"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/media?parent=858601"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/categories?post=858601"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/us\/wp-json\/wp\/v2\/tags?post=858601"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}![\"\"](\"https:\/\/www.newsbeep.com\/us\/wp-content\/uploads\/2026\/09\/d41586-026-03018-x_23939466.jpg\"\/)
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