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　　Liquid water may be found on planets that have gone adrift from their stars and may have acted as stepping stones to spread cosmic life, US researchers say。

　　Gravitational battles with other planets or passing stars can fling worlds out of their solar systems, but two scientists from the University of Chicago say these wandering worlds could continue to stay warm thanks to the decay of radioactive elements in their cores, NewScientist.com reported Monday。

　　Dorian Abbot and Eric Switzer say they've calculated that rocky planets with a mass similar to that of Earth could stay warm enough to keep water liquid under thick, insulating ice sheets for more than a billion years。

　　A planet with the same percentage of water as Earth could keep a subsurface ocean liquid if it was 3.5 times Earth's mass, they say, but a planet with 10 times Earth's water concentration could do this even if it weighed just one-third as much as Earth。

　　"It's a really interesting idea," Lisa Kaltenegger of the Harvard-Smithsonian Center for Astrophysics says of their theory. "But we would have to land on [a planet] and burrow down to see if life is possible."

　　美國研究者稱那些游離于星系之外的星球上可能有液態水，因而可能成為傳播宇宙生命的跳板。

　　在與其他星球和過往星宿的引力作用下，這些星球可能被甩出原來星球之外，然而美國芝加哥大學的兩位科學家稱星球內核里的放射物質衰敗所產生的熱量可以讓這些游離的星球保持一定溫度。

　　多利安?阿伯特和埃里克?斯維茨稱他們計算出一個體積與地球相當的巖石星球可以保持足夠溫度，使得水在厚厚的冰層下保持液態長達10萬年。

　　如果一個星球的含水比率和地球相當，體積是地球的3.5倍，那么地下海洋的水就能保持液態，但如果該星球的水儲藏量是地球的十倍，體積只有地球的三分之一，水也能保持液態。

　　哈佛?史密斯森中心的天體物理學研究人員莉莎?卡特尼格稱該理論“很有意思，但是得登陸這個星球，一探究竟，才能確定是否有生命跡象。”