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Recent observations of the surface of Mars have shown several fresh mid-latitude craters. Some of these craters show exposed ice (Byrne, S. et al. [2009]. Science 325, 1674-1676.). In some craters, albedo of ice slowly decreases, while in others, it remains nearly constant. We attempt to determine influence of the regolith structure on the rate of sublimation of ice. For this purpose we performed numerical simulations describing evolution of the exposed ice in model craters located at middle latitudes.We consider a new model for the structure and evolution of the material at- and beneath the crater floors. In contrast to the previous study by Dundas and Byrne (Dundas, C.M., Byrne, S. [2010]. Icarus 206, 716-728.) we do not investigate sublimation of dirty ice, and the related formation of a sublimation lag. Instead, we consider sublimation of a pure ice layer on top of layered regolith. In our model the observed reflectivity decreases due to the sublimation-driven changes of the optical properties of thinning clean ice. This offers an alternative to the deposition of the dust embedded in ice (sublimation lag).We have shown that in our model among many parameters affecting ice sublimation rate, volumetric fraction of water ice in the subsurface beneath the crater has the strongest influence. Hence observed darkening of the ice patch on the crater floor might be sufficient to determine the content of water ice in the subsurface. Our calculations show that an albedo decrease of fresh ice patches in mid-latitude craters can be explained by either strong dust sedimentation or, if this is excluded, by sublimation of a thin layer of water ice from the regolith with large thermal inertia. This is consistent with a large volumetric fraction of water ice beneath the crater floor and contributes to evidence for an extended subsurface water reservoir on Mars.The overall conclusion of our work is that a thin post-impact surface ice coating over ice-rich ground beneath the crater floors is consistent with the observations. 相似文献
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Enigmatic surface features, known as ‘spiders’, found at high southern martian latitudes, are probably caused by sublimation-driven erosion under the seasonal carbon dioxide ice cap. The Mars Reconnaissance Orbiter (MRO) High Resolution Imaging Science Experiment (HiRISE) has imaged this terrain in unprecedented details throughout southern spring. It has been postulated [Kieffer, H.H., Titus, T.N., Mullins, K.F., Christensen, P.R., 2000. J. Geophys. Res. 105, 9653-9700] that translucent CO2 slab ice traps gas sublimating at the ice surface boundary. Wherever the pressure is released the escaping gas jet entrains loose surface material and carries it to the top of the ice where it is carried downslope and/or downwind and deposited in a fan shape. Here we model two stages of this scenario: first, the cleaning of CO2 slab ice from dust, and then, the breaking of the slab ice plate under the pressure built below it by subliming ice. Our modeling results and analysis of HiRISE images support the gas jet hypothesis and show that outbursts happen very early in spring. 相似文献
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C.J. Hansen N. Thomas G. Portyankina A. McEwen T. Becker S. Byrne K. Herkenhoff H. Kieffer M. Mellon 《Icarus》2010,205(1):283-295
The High Resolution Imaging Science Experiment (HiRISE) on the Mars Reconnaissance Orbiter (MRO) has imaged the sublimation of Mars’ seasonal CO2 polar cap with unprecedented detail for one complete martian southern spring. In some areas of the surface, beneath the conformal coating of seasonal ice, radially-organized channels are connected in spidery patterns. The process of formation of this terrain, erosion by gas from subliming seasonal ice, has no earthly analog. The new capabilities (high resolution, color, and stereo images) of HiRISE enable detailed study of this enigmatic terrain. Two sites are analyzed in detail, one within an area expected to have translucent seasonal CO2 ice, and the other site outside that region. Stereo anaglyphs show that some channels grow larger as they go uphill - implicating gas rather than liquid as the erosive agent. Dark fans of material from the substrate are observed draped over the seasonal ice, and this material collects in thin to thick layers in the channels, possibly choking off gas flow in subsequent years, resulting in inactive crisscrossing shallow channels. In some areas there are very dense networks of channels with similar width and depth, and fewer fans emerging later in the season are observed. Subtle variations in topography affect the channel morphology. A new terminology is proposed for the wide variety of erosional features observed. 相似文献
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A. Pommerol N. Thomas M. Affolter G. Portyankina B. Jost K. Seiferlin K.-M. Aye 《Planetary and Space Science》2011,59(13):1601-1612
We have designed and constructed an original facility to characterize the VIS–NIR Bidirectional Reflectance Distribution Function (BRDF) and some complementary bulk physical properties of planetary analog samples containing water ice. The central part of the facility is a highly accurate gonio-radiometer (PHIRE-2) operating in the VIS–NIR spectral range (400–1100 nm) installed in a large laboratory freezer. Its development was based on the experience gained on the gonio-radiometer PHIRE-1 (Gunderson et al., 2006). The PHIRE-1 design was modified to permit operations at sub-zero temperatures and to optimize the performance of the instrument. The photometric measurements are complemented by a detailed simultaneous characterization of the physical state and possible temporal evolution of the samples using a combination of macro- and micro-imaging, thermal, electrical and sample mass measurements. The modified design will support the interpretation of current and future remote sensing and in-situ datasets on icy planetary objects with a special emphasis on cometary nuclei, Martian polar regions and Jovian satellites. 相似文献
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