South polar residual cap of Mars: Features, stratigraphy, and changes
South polar residual cap of Mars: Features, stratigraphy, and changes
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火星南极残留盖：特征、地层和变化
DOI：
10.1016/j.icarus.2004.07.028
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发表时间：
2005
期刊：
影响因子：
3.2
通讯作者：
P. Gierasch
中科院分区：
文献类型：
--
作者：
P. Thomas;M. Malin;P. James;B. Cantor;Rebecca M. E. Williams;P. Gierasch
火星南极残留冰帽富含CO2冰，与以H2O冰为主的北极残留冰帽在成分上存在差异。南冰冠在形态上也是独特的，显示出在薄层沉积物中形成的令人困惑的各种凹陷，这些凹陷被观察到在一个火星年的间隔内通过悬崖退缩而变化（Malin等人，2001，Science 294，2146-2148）。残留冰帽的气候敏感性表明，它们的行为可能有助于解释火星气候最近的波动或重复性。我们使用火星全球勘测者号火星轨道器相机（MOC）在三个南部夏季获得的图像来绘制南部残留帽的各种特征，并评估两个火星年（火星y）的变化。图像显示，存在两个不同的分层单元，其在不同的时间沉积，由降解期隔开。较老的单元，厚10米，层厚约2米。较年轻的单元有不同数量的层，每层厚约1.1米。较老的单位是侵蚀的陡崖后退平均3.6米/火星y，大于后退2.2米/火星y观察到的年轻的单位。陡崖后退的速率和不同类型凹陷的大小表明，残留帽盖的历史是短期沉积，其间穿插着较长的侵蚀期。旧单元的侵蚀可能需要100-150火星年。其中一层可能是在1972年水手9号观测之后沉积的。残余帽层似乎不同于正常的年度冬季存款有较高的孔隙度，也许有较高的孔隙度。这些属性可能产生的差异，影响在冬季沉积的高孔隙度雪的分数的沉积气象。
The south residual polar cap of Mars, rich in CO2ice, is compositionally distinct from the north residual cap which is dominantly H2O ice. The south cap is also morphologically distinct, displaying a bewildering variety of depressions formed in thin layered deposits, which have been observed to change by scarp retreat over an interval of one Mars year (Malin et al., 2001, Science 294, 2146–2148). The climatically sensitive locale of the residual caps suggests that their behavior may help in the interpretation of recent fluctuations or repeatability of the Mars climate. We have used Mars Global Surveyor Mars Orbiter Camera (MOC) images obtained in three southern summers to map the variety of features in the south residual cap and to evaluate changes over two Mars years (Mars y). The images show that there are two distinct layered units which were deposited at different times separated by a period of degradation. The older unit, ∼10 m thick, has layers approximately 2 m thick. The younger unit has variable numbers of layers, each ∼1 m thick. The older unit is eroding by scarp retreat averaging 3.6 m/Mars y, a rate greater than the retreat of 2.2 m/Mars y observed for the younger unit. The rates of scarp retreat and sizes of the different types of depressions indicate that the history of the residual cap has been short periods of deposition interspersed with longer erosional periods. Erosion of the older unit probably occupied ∼100–150 Mars y. One layer may have been deposited after the Mariner 9 observations in 1972. Residual cap layers appear to differ from normal annual winter deposits by having a higher albedo and perhaps by having higher porosities. These properties might be produced by differences in the depositional meteorology that affect the fraction of high porosity snow included in the winter deposition.