土衛四表面深層發現神祕海洋或潛在生命形式
A third Saturn moon may have a subsurface ocean with potential for life, researchers say.
研究人員日前表示，第三顆土星衛星可能存在表面深層海洋及潛在生命形式。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.
比利時皇家天文臺的研究人員表示，卡西尼探測器的最新引力數據表明，和土衛六以及土衛二一樣，土衛四的表面之下也有一個巨大海洋。Researchers say Dione's ocean is likely 100 kilometers beneath the surface, "several tens of kilometers deep" and surrounds a rocky core.
研究人員認爲，土衛四表層之下100千米處的這一巨大海洋深度足有數十千米，周圍包裹着岩石。
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.
和曾經在南極區域向太空噴射巨大水蒸汽流的土衛二不一樣，土衛四相對"安靜"，但是研究人員認爲它的表面遠古時期活動性更強。
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.
研究人員表示，土衛二的海洋比土衛四更接近表面，特別是在冰殼只有數千米厚的南極地區。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.
當時卡西尼探測器觀測到土衛二出現較大的前後振動，該現象叫做"天平動"，從而檢測到了海洋。如果土衛二天平動幅度更小，那麼這意味着其地殼更厚。"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."
"像土衛二一樣，土衛四也存在天平動，但是其振動幅度低於卡西尼探測器的探測等級。"研究報告聯合作者安東尼·鄭如是說，"未來探測器將在土星衛星周圍環繞，來測試我們的預測。"Dione's ocean has likely been there since the moon formed, researchers said, adding that it could be host to microbial life.
研究人員認爲，土衛四的海洋自衛星形成以來就存在了，這爲微生物提供了的宜居環境。"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."
"海洋和岩石內核之間的接觸是至關重要的。"研究報告聯合作者阿蒂利奧·利沃爾迪尼說道。"岩石和水之間的交互反應提供了關鍵的營養物質和能量源，以上是孕育生命的必要元素。"
