We examine the H₂O ice phase on the surface of Dione, one of Saturn’s icy satellites, to investigate whether it might harbor cryovolcanic activity induced by a subcrustal body of water. Several studies have searched for such a signature, as summarized in Buratti et al.; however, none has yet produced sufficient evidence to dissipate doubts. In the radiation environment characteristic of Saturn’s icy moons, the presence of crystalline H₂O ice has been used as a marker of a high-temperature region. Because ion bombardment will, over time, drive crystalline ice toward an increasingly amorphous state, the current phase of the H₂O ice can be used to gauge the temporal temperature evolution of the surface. We adopt a technique described by Dalle Ore et al. to map the fraction of amorphous to crystalline H₂O ice on Dione’s surface, observed by the Cassini Visible and Infrared Mapping Spectrometer, and provide an ice exposure age. We focus on a region observed at high spatial resolution and centered on one of the faults of the Wispy Terrain, which is measured to be fully crystalline. By assuming an amorphous to crystalline ice fraction of 5% (i.e., 95% crystallinity), significantly higher than the actual measurement, we obtain an upper limit for the age of the fault of 152 Ma. This implies that the studied fault has been active in the last ∼100 Ma, supporting the hypothesis that Dione might still be active or was active a very short time ago, and similarly to Enceladus, might still be harboring a body of liquid water under its crust.

我们检查了土星的冰卫星之一 Dione 表面的 H ₂ O 冰相，以研究它是否可能含有由地壳下水体诱发的冰冻火山活动。正如 Buratti 等人所总结的，有几项研究已经在寻找这样的特征；然而，还没有一个人提供足够的证据来打消疑虑。在土星冰卫星的辐射环境特征中，结晶H ₂ O冰的存在已被用作高温区域的标志。因为离子轰击会随着时间的推移将结晶冰推向越来越无定形的状态，即 H ₂的当前阶段O冰可用于测量表面的时间温度演变。我们采用了 Dalle Ore 等人描述的技术。映射无定形到结晶 H ₂的分数卡西尼号可见光和红外测绘光谱仪观察到迪奥内表面上的冰，并提供冰暴露年龄。我们专注于以高空间分辨率观察到的区域，并以 Wispy Terrain 的一个断层为中心，该断层被测量为完全结晶。通过假设 5% 的无定形到结晶冰的比例（即 95% 的结晶度），显着高于实际测量值，我们获得了 152 Ma 断层年龄的上限。这意味着所研究的断层在过去的 100 Ma 中一直处于活动状态，这支持了 Dione 可能仍然处于活动状态或在很短的时间内处于活动状态的假设，并且与土卫二类似，可能仍然在其下方藏有液态水体脆皮。