The extensive Medusae Fossae Formation (MFF) along the dichotomy boundary on Mars has geologic features indicative of wind erosion of low‐density material. There is evidence suggesting a water ice component, but with considerable uncertainty linked to the unknown MFF porosity and compaction behavior. We use SHARAD radar sounder data to estimate the real permittivity and loss tangent of MFF deposits, and compare these to a model for sediment compaction and to the properties of ice in mid‐latitude glaciers. In areas along the margins of Eumenides Dorsum, between Gordii Dorsum and Amazonis Mensa, and in northwest Zephyria Planum, the loss tangent is about 0.001 at 170 m and plateaus at about 0.003 for 310–550 m thickness. The real dielectric constant across the study areas ranges from 2 to 3. We propose that the MFF is a two‐layer deposit, with 300–600 m of fine‐grained, self‐compacting material above up to 2 km of minimally compacting, low‐loss material. The lower unit could be ice‐free and very coarse‐grained, but we see no evidence of extensive sand exposed by erosion. The lower layer might instead be ice‐rich and protected from sublimation by the dry cover. The volume of cover relative to a high ice content in the lower layer implies hybrid MFF formation as glacial or polar layered deposits capped by a dry, perhaps pyroclastic ash, component.

中文翻译：

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Medusae Fossae组的介电性质及其对含冰量的影响

沿火星二分边界的广泛的美杜莎化石组（MFF）具有指示低密度物质风蚀的地质特征。有证据表明存在水冰成分，但与未知的MFF孔隙度和压实行为有关，存在很大的不确定性。我们使用SHARAD雷达测深仪数据估算MFF沉积物的实际介电常数和损耗角正切，并将其与泥沙压实模型和中纬度冰川的冰质特性进行比较。在沿Eumenides Dorsum边缘，Gordii Dorsum和Amazonis Mensa之间以及西北Zephyria Planum的地区，厚度为310-550 m时，损耗角正切在170 m处约为0.001，高原在0.003处约为0.03。研究区域的实际介电常数范围为2到3。我们建议MFF是两层沉积，使用300–600 m的细颗粒，自密实的材料，在2 km以上的最小压实，低损耗的材料之上。下部单元可能没有冰并且颗粒非常粗大，但是我们没有发现侵蚀导致裸露的大量沙子的迹象。相反，下层可能富含冰层，并且受到干覆盖物的保护，不会升华。相对于下层高冰含量而言，覆盖物的体积意味着混合MFF形成为冰川或极性分层沉积物，被干燥的，可能为火山碎屑的灰分覆盖。