線狀谷底沉積

線狀谷底沉積 (Lineated valley fill),簡稱「LVF」,又叫線狀底表沉積(lineated floor deposit),是火星上某些谷道中的一種特徵,顯示為象被環流沖刷出道道溝脊的障礙物。陰影測量顯示,至少部分溝脊有數米高。據認為,這些線狀谷底沉積富含百米厚的水冰[1][2],並可能被保護在一層薄薄的岩殼下面[3][4][5]。這層岩殼由風載塵埃、碎落岩壁以及冰岩混合物中冰蒸發(從固態直接變成氣態)後的剩餘物所構成。地球上一些冰川也顯示了類似的脊狀。高解像度成像科學設備拍攝的高清照片顯示,部分線狀谷底沉積表面顯示出一層奇特的圖案,叫做細胞閉合型和細胞開放型腦紋地形。研究認為這種類似腦紋的地形,為堆積的塵埃和其他碎屑表面產生的裂紋以及部分表面冰升華所致,是重力和季節性冷熱變化共同作用的結果[6][7]舌狀岩屑坡同心坑沉積也顯示出這種相同的表面,因此,這三種結構的表面被認為有關聯性。

線狀底表沉積起始於舌狀岩屑坡(LDAs),當這些碎屑瀉入峽谷後就留在了狹窄的谷底,並攤開成一層覆蓋層[8]。通過追蹤舌狀岩屑坡的脊線路徑,研究人員逐漸相信舌狀岩屑坡彎曲的脊線會慢慢伸直,多少會變成較筆直的線狀谷底沉積脊線[5][9][10][11]。 在發生線狀谷底沉積和舌狀岩屑坡的區域,許多撞擊坑具有同心坑沉積:巨大的壟脊和類似人腦紋的「腦紋地形」表面[12]。 

西彌斯衛星、火星軌道相機、火星勘測軌道飛行器背景相機高解像度成像科學設備獲得的許多火星表面高品質圖像以及詳細的測高數據。這些大量的數據為研究線狀谷底沉積及其它特徵提供了極大的幫助。

火星勘測軌道器淺表層雷達接收到了分別來自舌狀岩屑坡頂部和底部發出的強烈反射信號,這意味着它的裏面大部分為純淨的水冰(在兩個反射信號之間),有力地證明了赫拉斯平原的舌狀岩屑坡為覆蓋着一層薄岩殼的冰川。由於線狀谷底地形來自於舌狀岩屑坡,因此,可能至少在某些地方含有被埋藏的冰[8][13][14]。  

與過去氣候的關係

對舌狀岩屑坡和線狀谷底沉積的研究表明,火星上曾發生過多次冰川活動,其中一次的冰川厚度接近一公里。這些大冰期與火星轉軸傾角大幅度變化所引起的氣候大變遷有關[15][16]。質量較大的月球阻止了地球傾角出現巨幅搖擺,而火星的兩顆衛星都很小,所以,火星會經歷一個讓極地冰蓋照射到更多直射陽光的大周期[17][18]。  在這段時期中,火星冰蓋中的冰會升華,厚厚的積雪降落在中緯度地區,而在這些地區,同心坑沉積、線狀山谷沉積和舌狀岩屑坡都很常見[19]。線狀谷底沉積上的撞擊坑分佈表明,至少在某些地區曾出現過亞馬遜紀 [1][20]

位置

在中緯度地區,尤其是是北部火星分界區附近,線狀谷底沉積很常見。尼羅瑟提斯桌山群普羅敦尼勒斯桌山群都特羅尼勒斯桌山群都有許多線狀谷底沉積的示例,伊斯墨諾斯湖區赫拉斯區的許多峽谷,也都顯示有線狀谷底沉積。 線狀山谷沉積及其他與冰有關的形式統稱為銳蝕地形,分佈在那些伴隨有孤聳高原和桌山群的蜿蜒或筆直峽谷中[21]

線狀谷底沉積的重要性

對線狀谷底沉積的研究補充了證明火星氣候在過去曾經歷許多巨大變化的證明[22]

有時下雪,有時雪會融化,由此產生的小面積液態水導致了岩石風化,可能為生命提供了有利的環境。理解線狀谷底沉積和其他冰貯藏的形式將可讓未來定居者能夠在火星上找到源。

魯爾谷, 如下圖所示,顯示了這些沉積物。有時,線狀底表沉積顯示出V形圖案,這是運動的進一步證據。下面這張由高解像度成像科學設備在魯爾谷拍攝的照片展示了這些圖案。

 

參見

參考文獻

  1. ^ 1.0 1.1 Head, J.; Marchant, D.R.; Agnew, M.C.; Fassett, C.I.; Kreslavsky, M.A. Extensive valley glacier deposits in the northern mid-latitudes of Mars: Evidence for late Amazonian obliquity-driven climate change. Earth Planet. Sci. Lett. 2006, 241 (3–4): 663–671. Bibcode:2006E&PSL.241..663H. doi:10.1016/j.epsl.2005.11.016. 
  2. ^ Head, J., et al.  2006. Modification if the dichotomy boundary on Mars by Amazonian mid-latitude regional glaciation.  Geophys. Res. Lett.  33
  3. ^ Morgan, G.;  Head,  James W.;  Marchant,  David R.  Lineated valley fill (LVF) and lobate debris aprons (LDA) in the Deuteronilus Mensae northern dichotomy boundary region, Mars: constraints on the extent, age, and episodicity of Amazonian glacial events. Icarus.  2009, 202 ( 1): 22–38. Bibcode:2009Icar..202...22M. doi:10.1016/j.icarus.2009.02.017. 
  4. ^ Head, J. and D. Marchant.  2006.  Evidence for global-scale northern mid-latitude glaciation in the Amazonian period of Mars:  Debris-covered glacial and valley glacial deposits in the 30 - 50 N latitude band.  Lunar. Planet. Sci. 37.  Abstract 1127
  5. ^ 5.0 5.1 Head, J.   & D. Marchant  . Modification of the walls of a Noachian crater in northern Arabia Terra (24E, 39N) during mid-latitude Amazonian glacial epochs on Mars: Nature and evolution of lobate debris aprons and their relationships to lineated valley fill and glacial systems. Lunar Planet. Sci. 2006,  37:  Abstract # 1126. 
  6. ^ Mellon, M.  1997.  Small-scale polygonal features on Mars:  Seasonal thermal contraction cracks in permafrost.  J. Geophysical Res: 102. 25,617-625,628.
  7. ^ Ley, J. et al.  2009.  Concentric crater fill in Utopia Planitia:  History and interaction between glacial "brain terrain" and periglacial processes.  Icarus: 202.  462-476.
  8. ^ 8.0 8.1 Souness C., Hubbard B. An alternative interpretation of late Amazonian ice flow: Protonilus Mensae, Mars. Icarus. 2013, 225 (1): 495–505. Bibcode:2013Icar..225..495S. doi:10.1016/j.icarus.2013.03.030. 
  9. ^ Kress, A., J. Head.  Ring-mold craters in lineated valley fill and lobate debris aprons on Mars: Evidence for subsurface glacial ice. Geophys. Res. Lett.  2008, 35 ( 23): L23206–8. 8GeoRL..3523206K Bibcode:200 8GeoRL..3523206K 請檢查|bibcode=值 (幫助). doi:10.1029/2008gl035501. 
  10. ^ Baker, D.; Head, James W.; Marchant, David R. Flow patterns of lobate debris aprons and lineated valley fill north of Ismeniae Fossae, Mars: Evidence for extensive mid-latitude glaciation in the Late Amazonian. Icarus. 2010, 207 (1): 186–209. Bibcode:2010Icar..207..186B. doi:10.1016/j.icarus.2009.11.017. 
  11. ^ Kress., A.   & J. Head  . Ring-mould craters on lineated valley fill, lobate debris aprons, and concentric crater fill on Mars: Implications for near-surface structure, composition, and age. Lunar Planet. Sci. 2009, 40: abstract 1379. 
  12. ^ Levy, J.; Head, James W.; Marchant, David R. Concentric crater fill in Utopia Planitia: History and interaction between glacial "brain terrain" and periglacial processes. Icarus. 2009, 202 (2): 462–476. Bibcode:2009Icar..202..462L. doi:10.1016/j.icarus.2009.02.018. 
  13. ^ Plaut, J. et al.  2008. Radar Evidence for Ice in Lobate Debris Aprons in the Mid-Northern Latitudes of Mars. Lunar and Planetary Science XXXIX.  2290.pdf
  14. ^ Head, JW; Neukum, G; Jaumann, R; Hiesinger, H; Hauber, E; Carr, M; Masson, P; Foing, B; et al. Tropical to mid-latitude snow and ice accumulation, flow and glaciation on Mars. Nature. 2005, 434 (7031): 346–350. Bibcode:2005Natur.434..346H. PMID 15772652. S2CID 4363630. doi:10.1038/nature03359. 
  15. ^ Madeleine, J. et al.  2007.  Exploring the northern mid-latitude glaciation with a general circulation model.  In: Seventh International Conference on Mars.  Abstract 3096.
  16. ^ Barlow, N.  2008.  Mars:  An Introduction to its Interior, Surface and Atmosphere.  Cambridge University Press.  ISBN 978-0-521-85226-5
  17. ^ 存档副本. [2020-11-03]. (原始內容存檔於2017-08-21). 
  18. ^ Forget, F., et al.  2006.  Planet Mars Story of Another World.  Praxis Publishing, Chichester, UK.  ISBN 978-0-387-48925-4
  19. ^ Carr, M.  2006.  The Surface of Mars.  Cambridge University Press.  ISBN 978-0-521-87201-0
  20. ^ Levy, J.; et al. Lineated valley fill and lobate debris apron stratigraphy in Nilosyrtis Mensae, Mars: Evidence for phases of glacialmodification of the dichotomy boundary. J. Geophys. Res. 2007, 112 (E8): E08004. Bibcode:2007JGRE..112.8004L. doi:10.1029/2006je002852. 
  21. ^ Sharp, R. Mars Fretted and chaotic terrains. J. Geophys. Res. 1973, 78 (20): 4073–4083. Bibcode:1973JGR....78.4073S. doi:10.1029/JB078i020p04073. 
  22. ^ Kreslavsky, M.   & J. Head  . Modification of impact craters in the northern planes of Mars: Implications for the Amazonian climate history. Meteorit. Planet. Sci. 2006, 41 (10): 1633–1646. Bibcode:2006M&PS...41.1633K. CiteSeerX 10.1.1.715.3727 . doi:10.1111/j.1945-5100.2006.tb00441.x . 

外部連結