Midlatitude slopes on Mars are mantled by deposits proposed to contain H₂O ice and dust, overlaid by a desiccated lag. However, direct evidence of their volatile content is lacking. Here we present novel evidence of light‐toned materials within midlatitude gully alcoves eroded into these mantles. The appearance and Lambert albedo of these materials suggests that they are either dust or H₂O ice. We interpret them to be H₂O ice because it is unlikely for a short‐term, localized dust deposit to form only within the mantle walls. The temperatures are generally too warm (>∼240 K) for the ice to be a frost in equilibrium. Therefore, this ice is likely similar to the dusty ice documented within midlatitude scarps, but with more dust, and exposed in smaller patches by slumping. It has been proposed that CO₂ frosts remove the overlying lag, causing the exposed H₂O ice to sublimate, liberate dust within the ice for transport, and erode gullies in the mantle. But we observe gullies eroded in wall rock that continue into the mantle, implying that the same process erodes both substrates. H₂O ice melt can explain gullies eroded in the wall rock and the mantle. Numerical models show that relatively dense H₂O snow on Mars melts only when it contains small amounts of dust. The observed exposure of dusty ice provides a mechanism for it to melt under some conditions and form some gullies. Access to liquid water within this ice could provide potential abodes for any extant life.

中文翻译：

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火星沟内暴露有尘水冰的证据

火星上的中纬度斜坡被提议包含H ₂ O冰和尘埃的沉积物覆盖，并被干燥的滞后物覆盖。然而，缺乏直接证明其挥发性含量。在这里，我们提供了中纬度沟壑内浅色物质侵蚀到这些地幔中的新颖证据。这些材料的外观和朗伯反照率表明它们是灰尘或H ₂ O冰。我们将其解释为H ₂结冰，因为短期的局部粉尘沉积不可能仅在地幔壁内形成。温度通常太高（>〜240 K），以至于冰在平衡时不会结霜。因此，这种冰很可能类似于中纬度陡峭带中记录的多尘冰，但尘埃更多，并因塌落而暴露在较小的斑块中。已经提出，CO ₂霜除去上覆的滞后，使暴露的H ₂ O冰升华，释放冰中的灰尘以便运输，并侵蚀地幔中的沟壑。但是，我们观察到沟壑在围岩中侵蚀，并继续进入地幔，这表明同一过程侵蚀了两种基质。高₂融冰可以解释沟壑侵蚀在围岩和地幔中的原因。数值模型表明，火星上相对密集的H ₂ O雪只有在包含少量粉尘时才会融化。观察到的尘土冰的暴露为它在某些条件下融化并形成一些沟壑提供了一种机制。在这块冰中接触液态水可能为任何现存生命提供潜在居所。