{"id":11529,"date":"2020-01-07T17:46:09","date_gmt":"2020-01-07T17:46:09","guid":{"rendered":"https:\/\/blogs.futura-sciences.com\/feldmann\/?p=11529"},"modified":"2020-01-30T05:28:18","modified_gmt":"2020-01-30T05:28:18","slug":"hippocampe-la-petite-lune-de-neptune-qui-nest-pas-a-sa-place","status":"publish","type":"post","link":"https:\/\/blogs.futura-sciences.com\/feldmann\/2020\/01\/07\/hippocampe-la-petite-lune-de-neptune-qui-nest-pas-a-sa-place\/","title":{"rendered":"Hippocampe, la petite lune de Neptune qui n&#8217;est pas \u00e0 sa place"},"content":{"rendered":"<p><strong>D\u00e9couverte autour de Neptune en 2013, la petite lune Hippocampe est sans doute un fragment de Prot\u00e9e dont elle est beaucoup trop proche.<\/strong><\/p>\n<h5>Chasseur de lunes :<\/h5>\n<p>L&#8217;astronome am\u00e9ricain <a href=\"https:\/\/www.seti.org\/our-scientists\/mark-showalter\" target=\"_blank\" rel=\"noopener noreferrer\">Mark Showalter<\/a> aime bien traquer les lointaines petites lunes dans le Syst\u00e8me solaire. On lui doit les d\u00e9couvertes de Pan autour de <a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2018\/09\/17\/saturne-la-planete-qui-fait-naitre-des-vocations\/\" target=\"_blank\" rel=\"noopener noreferrer\">Saturne<\/a>, Mab et Cupid du c\u00f4t\u00e9 d&#8217;<a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2014\/11\/20\/tempetes-geantes-sur-uranus\/\" target=\"_blank\" rel=\"noopener noreferrer\">Uranus<\/a> et Kerberos et Styx qui gravitent autour de <a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2018\/06\/21\/il-y-a-40-ans-on-decouvrait-charon-la-lune-de-pluton\/\" target=\"_blank\" rel=\"noopener noreferrer\">Pluton<\/a>. En 2013 il a rajout\u00e9 Hippocampe \u00e0 son tableau de chasse. Except\u00e9 pour Pan, toutes ses d\u00e9couvertes ont \u00e9t\u00e9 r\u00e9alis\u00e9es en analysant les images prises par le t\u00e9lescope spatial <a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2015\/04\/24\/en-video-science-et-poesie-pour-feter-le-telescope-hubble\/\" target=\"_blank\" rel=\"noopener noreferrer\">Hubble<\/a>.<\/p>\n<p><iframe loading=\"lazy\" title=\"Animation of Neptune\u2019s moon Hippocamp\" width=\"474\" height=\"267\" src=\"https:\/\/www.youtube.com\/embed\/nX3SCxp6Ww0?start=6&#038;feature=oembed\" frameborder=\"0\" allow=\"accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share\" referrerpolicy=\"strict-origin-when-cross-origin\" allowfullscreen><\/iframe><\/p>\n<h5>Tout au fond de la mer :<\/h5>\n<p>Hippocampe est un caillou d&#8217;une trentaine de kilom\u00e8tres de diam\u00e8tre. D\u00e9nicher un objet aussi petit \u00e0 plus de 4 milliards de kilom\u00e8tres est un d\u00e9fi de taille, m\u00eame avec le t\u00e9lescope spatial. Seule solution pour contourner la difficult\u00e9 : superposer plusieurs clich\u00e9s pour en augmenter la sensibilit\u00e9 et la r\u00e9solution. Un proc\u00e9d\u00e9 qu&#8217;utilisent tous les astrophotographes amateurs qui cherchent \u00e0 r\u00e9v\u00e9ler de faibles <a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2019\/04\/02\/les-astronomes-amateurs-decouvrent-encore-des-nebuleuses\/\" target=\"_blank\" rel=\"noopener noreferrer\">n\u00e9buleuses<\/a>. En lui ayant choisi ce nom, Mark Showalter s&#8217;est fait plaisir (il est passionn\u00e9 de plong\u00e9e) tout en restant dans le royaume de la mer du dieu <a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2016\/06\/16\/voyager-2-immortalisait-neptune-triton\/\" target=\"_blank\" rel=\"noopener noreferrer\">Neptune<\/a>.<!--more--><\/p>\n<h5>Curieuse proximit\u00e9 :<\/h5>\n<p>Mais la nouvelle petite lune n&#8217;est qu&#8217;\u00e0 12.000 kilom\u00e8tres de Prot\u00e9e, un imposant voisin de 400 kilom\u00e8tres de diam\u00e8tre. Les adeptes de la m\u00e9canique c\u00e9leste savent qu&#8217;une telle proximit\u00e9 entre deux satellites est impossible. Avec ses forces de mar\u00e9e, le plus massif \u00e9jecte le plus ch\u00e9tif ou l&#8217;attire pour une in\u00e9vitable collision. Les astronomes ont alors imagin\u00e9 un autre sc\u00e9nario pour Hippocampe. Selon eux la petite lune pourrait \u00eatre compos\u00e9e des restes de son imposante voisine. Ils ont imagin\u00e9 que l&#8217;impact d&#8217;une com\u00e8te sur Prot\u00e9e soit \u00e0 l&#8217;origine d&#8217;un nuage de d\u00e9bris dont la lente accr\u00e9tion aurait fini par donner naissance \u00e0 Hippocampe. T\u00e9moin de cet impact com\u00e9taire, le crat\u00e8re Pharos (250 kilom\u00e8tres de diam\u00e8tre) marque profond\u00e9ment le visage de Prot\u00e9e.<\/p>\n<h5>\u00c0 savoir :<\/h5>\n<p>Neptune est la huiti\u00e8me et derni\u00e8re plan\u00e8te du Syst\u00e8me solaire. Elle est la seule dont l&#8217;existence avait \u00e9t\u00e9 pr\u00e9dite par le calcul avant d&#8217;\u00eatre observ\u00e9e. Ce sont les perturbations inexpliqu\u00e9es de l&#8217;orbite d&#8217;Uranus qui ont incit\u00e9 John Couch Adams (en Angleterre) en 1843 et Urbain Le Verrier (en France) en 1846 \u00e0 calculer sa position th\u00e9orique. Elle a \u00e9t\u00e9 observ\u00e9e le 23 septembre 1846 par l&#8217;astronome allemand Johann Gottfried Galle. Neptune se trouvait alors \u00e0 1 degr\u00e9 de la position calcul\u00e9e par Le Verrier et \u00e0 12 degr\u00e9s de celle calcul\u00e9e par Adams.<\/p>\n<!-- AddThis Advanced Settings generic via filter on the_content --><!-- AddThis Share Buttons generic via filter on the_content -->","protected":false},"excerpt":{"rendered":"<p>D\u00e9couverte autour de Neptune en 2013, la petite lune Hippocampe est sans doute un fragment de Prot\u00e9e dont elle est beaucoup trop proche. Chasseur de lunes : L&#8217;astronome am\u00e9ricain Mark Showalter aime bien traquer les lointaines petites lunes dans le Syst\u00e8me solaire. On lui doit les d\u00e9couvertes de Pan autour de Saturne, Mab et Cupid &hellip; <a href=\"https:\/\/blogs.futura-sciences.com\/feldmann\/2020\/01\/07\/hippocampe-la-petite-lune-de-neptune-qui-nest-pas-a-sa-place\/\" class=\"more-link\">Continuer la lecture de <span class=\"screen-reader-text\">Hippocampe, la petite lune de Neptune qui n&#8217;est pas \u00e0 sa place<\/span>  <span class=\"meta-nav\">&rarr;<\/span><\/a><!-- AddThis Advanced Settings generic via filter on get_the_excerpt --><!-- AddThis Share Buttons generic via filter on get_the_excerpt --><\/p>\n","protected":false},"author":8,"featured_media":11530,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":"","_links_to":"","_links_to_target":""},"categories":[86],"tags":[2763,2764,642,2765],"class_list":["post-11529","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-soleil-et-planetes","tag-hippocampe","tag-mark-showalter","tag-neptune","tag-protee"],"yoast_head":"<!-- This site is optimized with the Yoast SEO plugin v24.1 - 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