Dao Vallis

Dao Vallis
Géographie
Astre
Mercure
Coordonnées
Longueur
794 km[1]Voir et modifier les données sur Wikidata
Quadrangle
Géologie
Types
Localisation sur la carte de Mars
voir sur la carte de Mars

Dao Vallis est une haute et large vallée de Mars de 1 200 km de long. Elle fait partie d'un système d'écoulement dans le quadrangle d'Hellas.

Désignation

Les grandes vallées martiennes reçoivent un nom rattaché à Mars ou bien la traduction du mot étoile dans diverses langues[2]. L'Union astronomique internationale (UAI) officialise le nom Dao Vallis en 2006, Dao signifiant « étoile » en thaï[3].

Géologie

Dao Vallis constitue un relief notable, dont les caractéristiques ont des implications importantes pour l'histoire du climat et de la géologie martiens[4].

Cartographie

Dao Vallis parcourt 1 200 km en partant du flanc sud-est du volcan Hadriacus Mons, traverse les hautes terres cratérisées du sud en direction du sud-ouest sur environ mille kilomètres et coupe les plaines sédimentaires du bord oriental du bassin d'Hellas, où elle s'interrompt[5],[6]. Son volume est estimé à 2,5 fois celui du second plus grand canyon terrestre, le Grand Canyon[7].

Formation

Vallées Dao, Niger, Harmakhis et Reull, rejoignant Hellas Planitia.

Dao Vallis fait partie des quatre principaux systèmes de canaux d'écoulement avec les vallées Niger, Harmakhis et Reull. Leur formation s'insère entre celle des vallées du Noachien et de l'Hespérien et celle des ravins et des cônes de débris (en) de l'Amazonien. La naissance de Dao Vallis sur les flancs d'un volcan et l'étude des données de THEMIS, Viking, MGS, Odyssey et MOLA conduisent à interpréter Dao Vallis comme résultant d'inondations éclair provoquées par la fonte brutale de grandes quantités de glace du sous-sol lors d'intrusions magmatiques, ainsi que d'effondrements dus à ce vidage du sous-sol, par effet de sape[4].

Dao Vallis et son affluent Niger Vallis

Les vallées Dao et Niger atteignent 40 km de large par endroits[8]. Au nord Dao Vallis est profond d'environ 2 400 m, avec un fond essentiellement lisse (ne comportant que des reliefs très érodés). Au sud son affluent Niger Vallis est profond d'environ 1 400 m[8]. Les deux vallées sont séparées par des plaines affaissées, sans doute à la suite d'écoulements souterrains[4].

Étude des matériaux et recherche de vie

Une équipe scientifique de la mission MRO a observé dans la région de Dao Vallis de la matière blanche étant possiblement de la glace d'eau poussiéreuse. Il pourrait y avoir une analogie entre les particules de poussière de cette glace et la poussière tombée sur les glaciers terrestres favorisant des poches d'eau souterraines appelées trous de cryoconite et abritant de la vie simple. Ce qui en ferait un endroit privilégié pour la recherche de vie sur Mars[9]. L'eau y a peut-être coulé il y a 3,5 millions d'années[10].

Matière blanche observée par Mars Reconnaissance Orbiter

Galerie

Notes et références

  1. Gazetteer of Planetary Nomenclature (base de données), IAU.Voir et modifier les données sur Wikidata
  2. (en) « Categories for naming features on Mars and martian satellites », Gazetteer of Planetary Nomenclature,‎ (lire en ligne [PDF])
  3. « Planetary Names », sur planetarynames.wr.usgs.gov (consulté le ).
  4. a b et c D. A. Crown, L. F. Bleamaster et S. C. Mest, « Geologic Evolution of Dao Vallis, Mars », AGU Fall Meeting Abstracts, vol. 2003,‎ , P11B–1035 (lire en ligne, consulté le )
  5. S. Kukkonen et V. -P. Kostama, « Modification history of the Harmakhis Vallis outflow channel, Mars, based on CTX-scale photogeologic mapping and crater count dating », Icarus, vol. 299,‎ , p. 46–67 (ISSN 0019-1035, DOI 10.1016/j.icarus.2017.07.014, lire en ligne, consulté le ).
  6. « HiRISE | Des ravins sur le mur sud de Dao Vallis, près de la confluence avec Niger Vallis (ESP_024315_1435) », sur www.uahirise.org (consulté le ).
  7. (en) Jarmo Korteniemi, « Detailed Mapping and Chronology of the Dao Vallis Canyon, Mars », Conference: Lunar and Planetary Institute Science Conference Abstracts,‎ (lire en ligne).
  8. a et b (en) « The eroded valleys of Dao and Niger Valles », sur www.esa.int (consulté le )
  9. (en-US) « Dusty Water Ice in Mars' Dao Vallis », sur NASA Jet Propulsion Laboratory (JPL) (consulté le ) : « On Earth, the dust that forms these pockets are called cryoconite, and the pockets are called cryoconite holes. These Earth-based pockets of water are often teeming with simple life, including algae, fungi and cyanobacteria. Scientists believe similar shallow pools of water could exist on Mars, and may also be excellent places to search for life on the Red Planet today. »
  10. (en) « Dao and Niger Valles », sur www.geo.fu-berlin.de, (consulté le )

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