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平原上部单元（upper plains unit）是在火星中纬度地区发现的50-10 … 平原上部单元（upper plains unit）是在火星中纬度地区发现的50-100米厚的覆盖层残余物，首次是在都特罗尼勒斯桌山群探测到，但其他地方也有出现。该残余层由撞击坑和洼地中以及沿台地分布的一系列倾斜结构层组成。倾斜层的大小和形状可能各不相同，有些看起来像来自中美洲的阿兹特克金字塔。
* 撞击坑中的层状结构，可能曾是覆盖面积更大的层状单元残剩部分，其构成物为从天空落下的冰核尘埃。该照片是高分辨率成像科学设备按照 HiWish 计划拍摄于希腊区。
* HiWish计划下高分辨率成像科学设备显示的位于希腊区的倾斜结构层。
* HiWish计划下高分辨率成像科学设备显示的希腊区倾斜层。
* HiWish计划下高分辨率成像科学设备显示的希腊区倾斜层。
* HiWish计划下高分辨率成像科学设备显示的倾斜层。
* HiWish计划下高分辨率成像科学设备显示的伊斯墨诺斯湖区一座桌山山体上的倾斜层近景图。
* HiWish计划下高分辨率成像科学设备显示的一座撞击坑中的倾斜结构层。
* HiWish项目指示下高分辨率成像科学设备显示的撞击坑中的层状特征。
* HiWish计划下高分辨率成像科学设备显示的撞击坑中的层状特征。
* 科罗拉多州红岩公园的层状特征，它的起源与火星上的不同，但形状相似，红岩区的特征是由山脉抬升引起的。
* HiWish计划下高分辨率成像科学设备显示的倾斜结构层。
* iWish计划下高分辨率成像科学设备显示的层状结构。
* iWish计划下高分辨率成像科学设备显示的倾斜结构层。 这种单元也会退化为脑纹地形，脑纹地形是一种3-5米高的迷宫状垄脊区。有些山脊可能由冰核芯构成，因此它们可能是未来定居者的水源。
* HiWish计划下高分辨率成像科学设备显示的希腊区一处小型层状结构，图片也显示了脑纹地形的形成。脑纹地形似乎起始于凹坑，而后变得越来越长，越来越复杂。
* 层状特征和脑纹地形，高分辨率成像科学设备显示，平原上部单元经常会转变为脑纹地形。
* 高分辨率成像科学设备显示脑纹地形形成于较厚的单元结构层。箭头显示较厚的单元分裂成小细胞。
* 正如HiWish计划下高分辨率成像科学设备显示的那样，脑纹地形是从上部平原单元的裂解中形成的。箭头指向的断裂处，正在转变为脑纹地形。
* 脑纹地形形成于平原上部单元的裂解，箭头所指的断裂处，正在转变为脑纹地形。 平原上部单元的一些区域显示出大裂缝和带有凸起边缘的凹槽，这些地区被称为棱状上部平原（Ribbed Upper Plains）。据信断裂起始于应力引起的小裂缝，因为当碎屑堆聚集到一起或靠近碎屑堆边缘时（这在棱状上部平原很常见），应力就会引发断裂作用。此类位置会产生挤压应力，使裂缝暴露出更多的表面，因此，材料中更多的冰会升华到行星稀薄的大气层中。最终，小裂缝逐惭演变成大峡谷或大槽沟。
* 发育良好的棱状上部平原地层，它们起始于小裂缝，随着冰从表面裂缝中升华而扩展。该照片为HiWish项目控制下的高分辨率成像科学设备所拍摄。
* HiWish计划下高分辨率成像科学设备显示的众多大小不一裂缝，由于地面冰的升华，左边的小裂缝会扩展得更大。裂缝暴露出更多的表面积，因此大大增加了火星稀薄空气中的升华现象。
* HiWish项目指示下的高分辨率成像科学设备也显示了倾斜层，图片右上角可看到棱状上部平原地层。它形成于平原上部单元，反过来又会被侵蚀为脑纹地形。
* 应力缝和因升华（冰直接气化）而被扩大的更大裂缝图，这可能是棱状地形的开始。
* 棱状地形演变自应力缝—左侧的裂缝终将会被扩大，并成为图右的棱状地形。
* HiWish计划下高分辨率成像科学设备显示的棱状地形和脑纹地形宽视图。
* 高分辨率成像科学设备显示，棱状地形形成于平原上部单元，起始于被升华促进的裂缝。方框显示足球场大小的区域。
* 背景相机拍摄的宽视图，显示了平原上部单元的下部与下方单元之间的联系。
* HiWish计划下高分辨率成像科学设备所显示，左侧的平原上部单元正在破裂，图片右侧存在一个较低的单元。
* 图中显示了平原上部物质如何破裂的细节，大量裂缝的形成似乎促进了裂解过程。
* 平原上部单元被侵蚀成凹洞的广角图，下一幅照片为局部放大图。
* 平原上部单元侵蚀成凹陷的特写，随着越来越多的冰从地面上消失，地表裂缝逐惭扩展。
* 凹陷或凹坑特定图 小裂缝通常包含小洞坑和洞坑链，被认为形成于地表冰的升华。火星表面大片区域都蕴含了水冰，冰被一层1米厚的灰尘和其他物质所保护。然而，一旦出现地表缝，将会使水冰暴露在稀薄的大气层中.，在很短时间内，冰将消失在寒冷稀薄的大气中，这一过程称为升华，干冰在地球上也有类似的行为。当凤凰号火星探测器发现裸露的冰块在几天内就消失了时，则在火星上观察到了升华的现象。此外，高分辨率成像科学设备还发现了坑底有冰的新陨坑，但隔了一段时间后，它看到的冰沉积物就已消失无踪了。
* 在四天的时间里，被挖开的“渡渡鸟-金凤花”沟中模具大小的白色块消失了，这意味着它们是由冰组成的，冰在暴露后就会升华 。
* 彩色照片显示了冰的升华，图片右上角插图为放大了的挖沟左下角。 据认为，平原上部单元来自于天空中飘落的物质，它覆盖在各种表面上，仿佛均匀落下。与其他沉积覆盖层一样，上部平原单元具有层状、细粒度和富含冰的特点，它分布普遍，似乎没有来源点。火星某些区域的表面外观是缘于该单元的退化，它也是造成舌状岩屑坡表面外观的主要原因之一据信，平原上部覆盖单元和其他覆盖单元的分层，是由该行星气候发生重大变化所致。模型预测，随着地质时间推移，火星自转轴倾角或倾斜度可能会从目前的25度改变到超过80度。高倾斜期间将导致火星极地冰盖中的冰重新分布，并改变大气中的尘埃含量。变到超过80度。高倾斜期间将导致火星极地冰盖中的冰重新分布，并改变大气中的尘埃含量。
, The upper plains unit is the remnants of a … The upper plains unit is the remnants of a 50-100 meter thick mantling that has been discovered in the mid-latitudes of the planet Mars. It was first investigated in the Deuteronilus Mensae (Ismenius Lacus quadrangle) region, but it occurs in other places as well. The remnants consist of sets of dipping layers in impact craters, in depressions, and along mesas. Sets of dipping layers may be of various sizes and shapes—some look like Aztec pyramids from Central America.
* Layered structure in crater that is probably what is left of a layered unit that once covered a much larger area. Material for this unit fell from the sky as ice-coated dust. The picture was taken by HiRISE, under the HiWish program. Picture is from Hellas quadrangle.
* Tilted layers, as seen by HiRISE under HiWish program Location is Hellas quadrangle.
* Tilted layers, as seen by HiRISE under HiWish program Location is Hellas quadrangle.
* Tilted layers, as seen by HiRISE under HiWish program Location is Hellas quadrangle.
* Dipping layers, as seen by HiRISE under HiWish program
* Close view of dipping layers along a mesa wall, as seen by HiRISE under HiWish program Location is Ismenius Lacus quadrangle.
* Dipping layers in a crater, as seen by HiRISE under HiWish program
* Layered features in crater, as seen by HiRISE under HiWish program
* Layered feature in crater, as seen by HiRISE under the HiWish program
* Layered feature in Red Rocks Park, Colorado. This has a different origin than ones on Mars, but it has a similar shape. Features in Red Rocks region were caused by uplift of mountains.
* Dipping layers, as seen by HiRISE under HiWish program
* Layered structures, as seen by HiRISE under HiWish program
* Dipping layers, as seen by HiRISE under HiWish program This unit also degrades into brain terrain. Brain terrain is a region of maze-like ridges 3–5 meters high. Some ridges may consist of an ice core, so they may be sources of water for future colonists.
* Small, layered structure, as seen by HiRISE under the HiWish program Picture also shows brain terrain forming. Brain terrain seems to start with pits that get longer and more complicated. Picture is from Hellas quadrangle.
* Layered features and brain terrain, as seen by HiRISE under HiWish program The upper plains unit often changes into brain terrain.
* Brain terrain being formed from a thicker layer, as seen by HiRISE under HiWish program. Arrows show the thicker unit breaking up into small cells.
* Brain terrain is forming from the breakdown of upper plains unit, as seen by HiRISE under HiWish program Arrow points to a place where fractures are forming that will turn into brain terrain.
* Brain terrain is forming from the breakdown of upper plains unit, as seen by HiRISE under HiWish program Arrow points to a place where fractures are forming that will turn into brain terrain. Some regions of the upper plains unit display large fractures and troughs with raised rims; such regions are called ribbed upper plains. Fractures are believed to have started with small cracks from stresses. Stress is suggested to initiate the fracture process since ribbed upper plains are common when debris aprons come together or near the edge of debris aprons—such sites would generate compressional stresses. Cracks exposed more surfaces, and consequently more ice in the material sublimates into the planet’s thin atmosphere. Eventually, small cracks become large canyons or troughs.
* Well developed ribbed upper plains material. These start with small cracks that expand as ice sublimates from the surfaces of the crack. Picture was taken with HiRISE under HiWish program
* Small and large cracks, as seen by HiRISE under HiWish program The small cracks to the left will enlarge to become much larger dues to sublimation of ground ice. A crack exposes more surface area, hence greatly increases sublimation in the thin Martian air.
* Dipping layers, as seen by HiRISE under HiWish program Also, Ribbed Upper plains material is visible in the upper right of the picture. It is forming from the upper plains unit, and in turn is being eroded into brain terrain.
* View of stress cracks and larger cracks that have been enlarged by sublimation (ice changing directly into gas) This may be the start of ribbed terrain.
* Evolution of ribbed terrain from stress cracks—cracks to the left eventually will enlarge and become ribbed terrain toward the right side of picture, as seen by HiRISE under HiWish program
* Wide view showing ribbed terrain and brain terrain, as seen by HiRISE under HiWish program
* Ribbed terrain being formed from upper plains unit, as seen by HiRISE under HiWish program Formation begins with cracks that enhance sublimation. Box shows the size of football field.
* Wide view showing contact between upper plains unit lower part of picture and a lower unit, as seen by CTX
* Contact, as seen by HiRISE under HiWish program Upper plains unit on the left is breaking up. A lower unit exists on the right side of picture.
* Close view of contact, as seen by HiRISE under HiWish program Picture shows details of how upper plains material is breaking. The formation of many fractures seems to proceed the break up.
* Wide view of upper plains unit eroding into hollows, as seen by HiRISE under HiWish program Parts of this image are enlarged in following images.
* Close view of upper plain unit eroding into hollows, as seen by HiRISE under HiWish program Break up begins with cracks on the surface that expand as more and more ice disappears from the ground.
* Close view of hollows, as seen by HiRISE under HiWish program Small cracks often contain small pits and chains of pits; these are thought to be from sublimation of ice in the ground.Large areas of the Martian surface are loaded with ice that is protected by a meters thick layer of dust and other material. However, if cracks appear, a fresh surface will expose ice to the thin atmosphere. In a short time, the ice will disappear into the cold, thin atmosphere in a process called sublimation. Dry ice behaves in a similar fashion on the Earth. On Mars sublimation has been observed when the Phoenix lander uncovered chunks of ice that disappeared in a few days. In addition, HiRISE has seen fresh craters with ice at the bottom. After a time, HiRISE saw the ice deposit disappear.
* Die-sized clumps of bright material in the enlarged "Dodo-Goldilocks" trench vanished over the course of four days, implying that they were composed of ice which sublimated following exposure.
* Color versions of the photos showing ice sublimation, with the lower left corner of the trench enlarged in the insets in the upper right of the images. The upper plains unit is thought to have fallen from the sky. It drapes various surfaces, as if it fell evenly. As is the case for other mantle deposits, the upper plains unit has layers, is fine-grained, and is ice-rich. It is widespread; it does not seem to have a point source. The surface appearance of some regions of Mars is due to how this unit has degraded. It is a major cause of the surface appearance of lobate debris aprons.The layering of the upper plains mantling unit and other mantling units are believed to be caused by major changes in the planet’s climate. Models predict that the obliquity or tilt of the rotational axis has varied from its present 25 degrees to maybe over 80 degrees over geological time. Periods of high tilt will cause the ice in the polar caps to be redistributed and change the amount of dust in the atmosphere.ange the amount of dust in the atmosphere.
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