The evolution of the albedo of dark spots observed on Mars polar region
The evolution of the albedo of dark spots observed on Mars polar region
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DOI：
10.1016/j.icarus.2012.09.008
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发表时间：
2012-11-01
期刊：
影响因子：
3.2
通讯作者：
Elliott, H. M.
中科院分区：
文献类型：
--
作者：
Martinez, G. M.;Renno, N. O.;Elliott, H. M.
我们提出了一种方法来消除大气的影响，从高分辨率成像科学实验数据，以计算在近红外（0.8-1 μ m），红色（0.55-0.85 μ m），蓝色绿色（0.4-0.6 μ m）光谱波段的火星表面的反射率。我们的方法的应用结果在高达20%的修正，在卫星测量的最大值。本文利用火星表面反射波的时间演化来研究在火星南极地区理查森环形山观测到的暗斑。这些黑点在冬末形成，在春末消失。它们具有很高的科学兴趣，因为它们似乎是由颗粒物质、液体或两者的组合的流动引起的。除图像外，以下数据在我们的研究中用作辅助信息：由热发射成像系统测量得出的尘埃光学深度，由火星小型侦察成像光谱仪探测到的CO2冰或H2O冰的存在，由热发射光谱仪测量得出的表面压力和温度值，最后进行了动力学计算和数值模拟，结果支持了以前提出的气体排放假说，以解释暗斑的形成。我们表明，喷射的CO2气体和伴随的松散的材料，通过在半透明的CO2冰层的裂缝，建议由这个假设，是一致的时间演变的表面冰。一旦暗点形成，表面的反射值表明它们有三个不同的区域：中心的暗核，周围的亮区（被许多作者称为亮晕），以及将暗核与亮晕分开的光学上不同的中间区域。我们的分析表明，这三个地区是物理上不同的，CO2和H2O冰的沉积和升华是必要的，以解释的时间演变的暗斑和周围地区的时间演变。然而，这些传统的机制不能解释一些观察到的功能，如一个意想不到的减少和随后的增加，而表面温度不断上升的热释电。我们假设，这种意想不到的减少是由盐水形成，并提出了一种机制来解释它。一个新的喷射的黑暗物质或尘埃沉积也可以解释这种减少。然而，我们表明，这些过程是不可能的原因，减少的碳同位素。在理查森陨石坑观测到的黑点含有液态盐水的假设可以通过实验室实验或未来着陆器的现场测量来验证。(C)2012 Elsevier Inc. All rights reserved.
We present a methodology to remove atmospheric effects from High Resolution Imaging Science Experiment data in order to calculate the albedo of the martian surface in the near infrared (0.8-1 mu m), red (0.55-0.85 mu m), and blue green (0.4-0.6 mu m) spectral bands. The application of our methodology results in corrections of up to 20% in the albedo measured by the satellite. Time evolution of the surface albedo is used to study dark spots observed in Richardson Crater, on Mars south polar region. These dark spots form in late winter and vanish in late spring. They are of high scientific interest because they appear to be caused by the flow of granular material, liquid, or a combination of both. Besides images, the following data are used as ancillary information in our study: dust optical depth derived from measurements by the Thermal Emission Imaging System, the detection of the presence of either CO2 ice or H2O ice by the Compact Reconnaissance Imaging Spectrometers for Mars, surface pressure and temperature values derived from measurements by the Thermal Emission Spectrometer, and finally kinetic calculations and numerical modeling.Our results support the gas venting hypothesis previously proposed to explain the formation of dark spots. We show that the ejection of CO2 gas and accompanying loose material through cracks in the translucent CO2 ice layer, suggested by this hypothesis, is consistent with the time evolution of the surface albedo. Once dark spots form, surface albedo values indicate that they have three distinct areas: a dark core at their center, a brighter zone surrounding them (referred to as bright halo by various authors), and an optically distinct intermediate area separating the dark core from the bright halo. Our analysis indicates that these three areas are physically distinct and that the deposition and sublimation of CO2 and H2O ices are necessary to explain the time evolution of the albedo of the dark spots and the areas surrounding them. However, these conventional mechanisms cannot explain some observed features such as an unexpected decrease and subsequent increase in albedo while the surface temperature raises continuously. We hypothesize that this unexpected decrease in albedo is caused by brine formation and propose a mechanism to explain it. A new ejection of dark material or dust deposition could also explain this decrease. However, we show that these processes are unlikely to be the cause of the albedo decrease. The hypothesis that the dark spots observed in Richardson Crater contain liquid brines can be tested with laboratory experiments or in situ measurements by future landers. (C) 2012 Elsevier Inc. All rights reserved.