A third Saturn moon may have a subsurface ocean with potential for life, researchers say.研究人员日前回应，第三颗土星卫星有可能不存在表面深层海洋及潜在生命形式。Using gravity data from the Cassini probe, researchers at the Royal Observatory of Belgium say Dione joins Titan and Enceladus as Saturn moons likely having subsurface oceans.比利时皇家天文台的研究人员回应，卡西尼探测器的近期引力数据指出，和土卫六以及土卫二一样，土卫四的表面之下也有一个极大海洋。

Researchers say Diones ocean is likely 100 kilometers beneath the surface, several tens of kilometers deep and surrounds a rocky core.研究人员指出，土卫四表层之下100千米处的这一极大海洋深度脚有数十千米，周围包覆着岩石。Unlike Enceladus, which has geysers of water that spurt from the southern polar region, Dione appears quiet now, but researchers say it likely had a more active past.和曾多次在南极区域向太空喷气极大水蒸汽东流的土卫二不一样，土卫四比较安静，但是研究人员指出它的表面远古时期活动性更加强劲。Enceladus ocean, according to researchers, is likely much closer to the surface, particularly in the southern polar regions where the icy crust might be only a few kilometers thick.研究人员回应，土卫二的海洋比土卫四更加相似表面，特别是在冰壳只有数千米薄的南极地区。

One way Enceladus ocean was discovered was by observing large back-and-forth oscillations, called libration. If the libration was smaller on the moon, it would likely mean the crust was thicker.当时卡西尼探测器观测到土卫二经常出现较小的前后振动，该现象叫作天平一动，从而检测到了海洋。如果土卫二天平一动幅度更加小，那么这意味著其地壳更加薄。

Like Enceladus, Dione librates but below the detection level of Cassini, said Antony Trinh, co-author of the new study. A future orbiter hopping around Saturns moons could test this prediction.像土卫二一样，土卫四也不存在天平一动，但是其振动幅度高于卡西尼探测器的观测等级。研究报告牵头作者安东尼·郑如是说，未来探测器将在土星卫星周围环绕着，来测试我们的预测。

Diones ocean has likely been there since the moon formed, researchers said, adding that it could be host to microbial life.研究人员指出，土卫四的海洋自卫星构成以来就不存在了，这为微生物获取了的宜居环境。The contact between the ocean and the rocky core is crucial, said Attilio Rivoldini, co-author of the study. Rock-water interactions provide key nutrients and a source of energy, both being essential ingredients for life.海洋和岩石内核之间的认识是至关重要的。

研究报告牵头作者阿蒂利奥·利沃尔迪尼说。岩石和水之间的交互反应获取了关键的营养物质和能量源，以上是孕育出生命的适当元素。

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