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."

　　美国研究者称那些游离于星系之外的星球上可能有液态水，因而可能成为传播宇宙生命的跳板。

　　在与其他星球和过往星宿的引力作用下，这些星球可能被甩出原来星球之外，然而美国芝加哥大学的两位科学家称星球内核里的放射物质衰败所产生的热量可以让这些游离的星球保持一定温度。

　　多利安•阿伯特和埃里克•斯维茨称他们计算出一个体积与地球相当的岩石星球可以保持足够温度，使得水在厚厚的冰层下保持液态长达10万年。

　　如果一个星球的含水比率和地球相当，体积是地球的3.5倍，那么地下海洋的水就能保持液态，但如果该星球的水储藏量是地球的十倍，体积只有地球的三分之一，水也能保持液态。

　　哈佛•史密斯森中心的天体物理学研究人员莉莎•卡特尼格称该理论“很有意思，但是得登陆这个星球，一探究竟，才能确定是否有生命迹象。”