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A third Saturn moon may have a subsurface ocean with potential for life, researchers say.
研究人员日前表示，第三颗土星卫星可能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表示，卡西尼探测器的最新引力数据表明，和土卫六以及土卫二一样，土卫四的表面之下也有一个巨大海洋。
Researchers say Dione's ocean is likely 100 kilometers beneath the surface, "several tens of kilometers deep" and surrounds a rocky core.
研究人员认为，土卫四表层之下100千米处的这一巨大海洋深度足有数十千米，周围包裹着岩石。
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.
和曾经在南极区域向太空喷射巨大水蒸汽流的土卫二不一样，土卫四相对"安静"，但是研究人员认为它的表面远古时期活动性更强。
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.
研究人员表示，土卫二的海洋比土卫四更接近表面，特别是在冰壳只有数千米厚的南极地区。
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出现较大的前后振动，该现象叫做"天平动"，从而检测到了海洋。如果土卫二天平动幅度更小，那么这意味着其地壳更厚。
"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 Saturn's moons could test this prediction."
"像土卫二一样，土卫四也存在天平动，但是其振动幅度低于卡西尼探测器的探测等级。"研究报告联合作者安东尼·郑如是说，"未来探测器将在土星卫星周围环绕，来测试我们的预测。"
Dione's ocean has likely been there since the moon formed, researchers said, adding that it could be host to microbial life.
研究人员认为，土卫四的海洋自卫星形成以来就存在了，这为微生物提供了的宜居环境。
"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接触是至关重要的。"研究报告联合作者阿蒂利奥·利沃尔迪尼说道。"岩石和水之间的交互反应提供了关键的营养物质和能量源，以上是孕育生命的必要元素。"
