土卫二上有生命吗？（图）   

 

Life on Enceladus?

Spouting plumes of ice and water vapor certainly make Enceladus one of the solar system's liveliest places. But continuing studies of the composition of those plumes are now making Saturn's icy moon the most promising place to look for extraterrestrial life. Researchers reported at a May meeting and online today in Nature that the best sampling yet of the plumes by the Cassini spacecraft reveals strong evidence for liquid water beneath the deeply frigid surface—an ocean, a sea, or at least water-filled cracks. Solid ice had been a contender to explain the gases and particles found in the plumes. But Cassini observations, including ever-rising estimates of the amount of heat given off by the moon, were challenging the ice-only source. Now analyses of Cassini data from a flyby through the heart of the plumes show that 99% of the mass of plume ice-particles is salt-rich. That alone strongly implies that the water in plume ice came from salty liquid water somewhere beneath the surface, say the researchers. Direct proof of a watery interior must likely await another mission, which may not come for decades.

土卫二不断地喷涌出含有冰和水汽的羽流，理所当然地使其成为太阳系最为活跃的地方之一。然而，对那些羽流中的成分进行的不断研究发现，土星的这颗冰封的卫星竟然成为最有希望找到地外生命的地方。在五月份的一次会议上，并且在今天的《自然》杂志上，研究人员报道说：“卡西尼”号太空船为土卫二的羽流进行了最完整的采样，显示出强有力的证据表明，在深深冻结的土卫二表面下拥有液态水——可能是一片大海、一片汪洋，或者至少拥有充满水的缝隙。过去，坚冰一直被认为是羽流中的一种成分，可以用来解释其中的气体和颗粒。但是，“卡西尼”号进行的观察，包括对土卫二释放热量的估值不断上升，使仅仅有冰的观念受到挑战。现在，对“卡西尼”号飞越羽流中心时获得的资料所进行的分析表明，大量的羽流冰粒中，99%富含盐分。研究人员说，仅此一点就可以有力地说明，羽流中的冰来自表面下某处含盐的液态水。内部含有水的直接证据可能必须要等到下一次航天行动，那可能是几十年以后的事情了。