{"id":193,"date":"2021-12-02T12:45:12","date_gmt":"2021-12-02T11:45:12","guid":{"rendered":"https:\/\/kids.esa.int\/comets\/"},"modified":"2026-10-08T00:25:20","modified_gmt":"2026-10-07T22:25:20","slug":"comets","status":"publish","type":"post","link":"https:\/\/kids.esa.int\/fi\/comets\/","title":{"rendered":"Komeetat"},"content":{"rendered":"
\n

Muinaiset ihmiset pelk\u00e4siv\u00e4t komeettoja \u2013 niiden sanottiin tuovan huonoa onnea tai ennustavan katastrofeja. Nyky\u00e4\u00e4n tied\u00e4mme, ett\u00e4 komeetat ovat pieni\u00e4 j\u00e4\u00e4maailmoja, jotka ovat j\u00e4\u00e4neet j\u00e4ljelle planeettojen muodostumisen j\u00e4lkeen. Aurinkokunnan reunalla, Pluton kiertoradan ulkopuolella, arvioidaan olevan miljardeja komeettoja.<\/p>\n<\/div>\n

Suurin osa komeetoista on niin pieni\u00e4 ja niin kaukana, ettemme n\u00e4e niit\u00e4 edes suurimmilla kaukoputkilla. Voimme kuitenkin n\u00e4hd\u00e4 ne, kun ne l\u00e4hestyv\u00e4t Aurinkoa ja niille muodostuu kaasu- ja p\u00f6lyh\u00e4nti\u00e4. (Sana \u2018komeetta\u2019 tarkoittaa \u201dkarvaista t\u00e4hte\u00e4\u201d.)<\/p>\n

Auringon l\u00e4mp\u00f6 saa j\u00e4\u00e4n muuttumaan kaasuksi, joka virtaa miljoonia kilometrej\u00e4 avaruuteen. Pituudestaan huolimatta niiss\u00e4 olevat p\u00f6lyhiukkaset eiv\u00e4t ole hiekanjyvi\u00e4 suurempia.<\/p>\n

\"Rosetta
Rosetta \u2013 komeettojen jahtaaja<\/figcaption><\/figure>\n

Joidenkin komeettojen kiertoaika Auringon ymp\u00e4ri kest\u00e4\u00e4 vain muutaman vuoden. Toisilla \u2013 kuten Halleyn komeetalla \u2013 se kest\u00e4\u00e4 paljon kauemmin. Toiset n\u00e4kyv\u00e4t vain kerran, eik\u00e4 niit\u00e4 en\u00e4\u00e4 koskaan n\u00e4hd\u00e4. ESAn SOHO-avaruusluotaimen avulla on l\u00f6ydetty tuhansia pieni\u00e4 komeettoja, jotka lent\u00e4v\u00e4t hyvin l\u00e4hell\u00e4 Aurinkoa. Monet niist\u00e4 t\u00f6rm\u00e4\u00e4v\u00e4t Aurinkoon tai hajoavat sen voimakkaan painovoiman vaikutuksesta.<\/p>\n

Vuonna 2014 eurooppalainen Rosetta-avaruusluotain tekee historiaa siirtym\u00e4ll\u00e4 komeetan kiertoradalle ja laskemalla laskeutumisaluksen sen pinnalle.<\/p>","protected":false},"excerpt":{"rendered":"

Ancient people were afraid of comets \u2013 they were said to bring bad luck or foretell disaster. We now know that comets are small ice worlds that have been left […]<\/p>\n","protected":false},"author":5,"featured_media":0,"comment_status":"closed","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"_jetpack_newsletter_access":"","_jetpack_dont_email_post_to_subs":false,"_jetpack_newsletter_tier_id":0,"_jetpack_memberships_contains_paywalled_content":false,"esa_banner_image":"https:\/\/www.esa.int\/var\/esa\/storage\/images\/esa_multimedia\/images\/2003\/04\/giotto_s_art_shows_a_comet_in_the_background2\/17913109-2-eng-GB\/Giotto_s_art_shows_a_comet_in_the_background.jpg","esa_banner_description":"Giotto's art shows a comet in the background","esa_banner_credit":"ESA","esa_banner_licence":"ESA Standard Licence","esa_banner_detail_url":"https:\/\/www.esa.int\/ESA_Multimedia\/Images\/2003\/04\/Giotto_s_art_shows_a_comet_in_the_background2","esa_external_url":"","esa_external_new_window":false,"_jetpack_feature_clip_id":0,"_jetpack_memberships_contains_paid_content":false,"footnotes":"","jetpack_post_was_ever_published":true},"categories":[46,10,11],"tags":[2],"panel":[],"language":[],"age":[],"duration":[],"resource_type":[],"audience":[],"wf_post_folders":[],"class_list":["post-193","post","type-post","status-publish","format-standard","hentry","category-comets-and-meteors","category-learn","category-our-universe","tag-background-article"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/posts\/193","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/users\/5"}],"replies":[{"embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/comments?post=193"}],"version-history":[{"count":4,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/posts\/193\/revisions"}],"predecessor-version":[{"id":4350,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/posts\/193\/revisions\/4350"}],"wp:attachment":[{"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/media?parent=193"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/categories?post=193"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/tags?post=193"},{"taxonomy":"panel","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/panel?post=193"},{"taxonomy":"language","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/language?post=193"},{"taxonomy":"age","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/age?post=193"},{"taxonomy":"duration","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/duration?post=193"},{"taxonomy":"resource_type","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/resource_type?post=193"},{"taxonomy":"audience","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/audience?post=193"},{"taxonomy":"wf_post_folders","embeddable":true,"href":"https:\/\/kids.esa.int\/fi\/wp-json\/wp\/v2\/wf_post_folders?post=193"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}