Magnetic fields<\/a> require a dynamo: conductive material churning in the deep interior, generating electrical currents that sustain the field. <\/p>\n Planets do this routinely. Ganymede<\/a>, uniquely among moons, seems to do it as well.<\/p>\n A new paper proposes an answer \u2013 and if it\u2019s right, Ganymede isn\u2019t just unusual. It\u2019s unique in a way that nobody anticipated.<\/p>\n The magnetic field, the researchers suggest, may be powered by a core that is still forming.\u00a0<\/p>\n The standard explanation<\/p>\n The way Earth generates its magnetic field is reasonably well understood. The outer core \u2013 a shell of liquid iron and nickel surrounding the solid inner core \u2013 churns constantly, driven by heat and compositional differences.\u00a0<\/p>\n Those motions generate electrical currents which sustain the magnetic field. It\u2019s been running for billions of years, and it\u2019ll keep running as long as the core stays liquid enough to move.<\/p>\n For Ganymede, researchers proposed a variation called iron snow. The idea is that liquid iron near the top of the core cools enough to crystallize, sinks through the warmer liquid below, and re-melts deeper down.\u00a0<\/p>\n That cycling motion drives the convection the dynamo needs. It\u2019s plausible, and for a while it was the leading explanation.<\/p>\n But it rests on the assumption that Ganymede formed hot enough \u2013 and early enough \u2013 for metals<\/a> to separate out and build a core back when the Solar System was young.\u00a0<\/p>\n Some researchers have questioned that assumption. They argue that icy moons<\/a> may have formed too cold for rapid differentiation \u2013 the process that separates dense metals from lighter material and builds a core. <\/p>\n If so, Ganymede\u2019s core could be far less developed than scientists have assumed.<\/p>\n A core building in slow motion<\/p>\n Kevin Trinh, a planetary scientist at Caltech<\/a>, and his colleagues decided to take that cold-start scenario seriously and model what would happen.<\/p>\n In their simulations, Ganymede begins cold and warms gradually over billions of years \u2013 heated by the radioactive decay of heavy elements in its rocks and by the constant gravitational kneading of Jupiter\u2019s enormous tidal pull. <\/p>\n Over time, that warmth does two things.\u00a0It releases water from the rocks, feeding the vast subsurface ocean Ganymede is known to have. <\/p>\n The heat also melts iron-rich material. This begins a long, slow trickle down toward the moon\u2019s center, building a core grain by grain over geological time.<\/p>\n As that iron drips in and accumulates, it stirs the liquid interior around it. Fresh, dense metal arriving continuously drives convection \u2013 and that convection is enough to sustain a magnetic dynamo.\u00a0<\/p>\n In many of their simulations, this process is still running today. The core isn\u2019t finished and the act of building it is what generates the magnetic field.<\/p>\n \u201cI\u2019m used to thinking of core formation being this ancient process,\u201d Trinh said. The new model suggests it might be delayed by billions of years in the right circumstances.<\/p>\n A narrow range of conditions<\/p>\n There\u2019s a reason this scenario hasn\u2019t been proposed before. It only works within a fairly narrow range of conditions.\u00a0<\/p>\n If Ganymede had started out too cold, the iron would never have melted and begun separating at all. <\/p>\n If it had started out too hot, the core would have finished forming long ago. This mechanism would have shut down before humans ever existed to wonder about it.<\/p>\n Ganymede, in this picture, happened to form under conditions that have kept the process running for billions of years and haven\u2019t finished yet. <\/p>\n That\u2019s a remarkable coincidence, and some researchers are understandably cautious about it.<\/p>\n Some questions still remain<\/p>\n \u201cIn principle, the story sounds interesting and reasonable,\u201d said Doris Breuer, a planetary scientist at the German Aerospace Center<\/a>, who wasn\u2019t involved in the study.\u00a0<\/p>\n But with so many factors in play, she\u2019s not totally convinced the model has accounted for everything.<\/p>\n Tina R\u00fcckriemen-Bez, a planetary scientist at the University of M\u00fcnster<\/a> who reviewed the paper, put the broader implication plainly. <\/p>\n If the still-forming core turns out to be real, \u201cmaybe people have to revise how they think about magnetic field generation.\u201d<\/p>\n The next chapter<\/p>\n The good news is that this won\u2019t stay a theoretical question for much longer. <\/p>\n The European Space Agency\u2019s JUICE mission<\/a> (Jupiter Icy Moons Explorer) is on its way and due to arrive at Ganymede in 2031.\u00a0<\/p>\n Its instruments will measure the moon\u2019s gravity field with enough precision to reveal how mass is distributed in the deep interior. <\/p>\n The mission will clarify whether iron<\/a> is concentrated in a compact, fully formed core, or still spread more broadly through the moon\u2019s insides.\u00a0<\/p>\n Magnetic measurements will add further detail about the core\u2019s size and state.<\/p>\n A world that\u2019s still evolving<\/p>\n If the measurements confirm that the core is still forming, Ganymede will become something genuinely without parallel in the known Solar System. <\/p>\n It would be the only world where a process scientists assumed ended billions of years ago is still quietly unfolding today.<\/p>\n Galileo\u2019s 1996 flyby made Ganymede unique among moons. Nearly three decades of thinking about what that magnetic field means has led to a suggestion that it might be unique among worlds entirely.<\/p>\n The study is published in the journal Science Advances<\/a>.<\/p>\n \u2014\u2013<\/p>\n Like what you read? Subscribe to our newsletter<\/a> for engaging articles, exclusive content, and the latest updates.<\/p>\n Check us out on EarthSnap<\/a>, a free app brought to you by Eric Ralls<\/a> and Earth.com<\/a>.<\/p>\n \u2014\u2013<\/p>\n","protected":false},"excerpt":{"rendered":"In 1996, NASA\u2019s Galileo spacecraft flew past Ganymede, Jupiter\u2019s largest moon and the largest moon in the Solar…\n","protected":false},"author":2,"featured_media":455927,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[23],"tags":[111,139,69,147,392],"class_list":["post-455926","post","type-post","status-publish","format-standard","has-post-thumbnail","category-space","tag-new-zealand","tag-newzealand","tag-nz","tag-science","tag-space"],"_links":{"self":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/455926","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/comments?post=455926"}],"version-history":[{"count":0,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/posts\/455926\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media\/455927"}],"wp:attachment":[{"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/media?parent=455926"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/categories?post=455926"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.newsbeep.com\/nz\/wp-json\/wp\/v2\/tags?post=455926"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}
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\n<\/a><\/p>\n