86 Life on Other Planets?

Since early times, people have been fascinated with the idea of life existing somewhere else besides Earth. Until recently, scientists believed that extraterrestrial life was just a hopeful dream. But now they are beginning to locate places where life could form. In 1997, they saw evidence of planets near other stars like the sun. Planets are places that might have the basic conditions for life. But scientists now think that life could be even nearer, in our own solar system.

One place scientists are studying very closely is Europa, a moon of Jupiter. Space probes have provided evidence that Europa has a large ocean under its surface. The probes have also made scientists think that under its surface Europa has a rocky core giving off volcanic heat. Water and heat from volcanic activity are two basic conditions needed for life to form. A third is certain basic chemicals such as carbon, oxygen, and nitrogen. Comets and meteorites carrying these chemicals have certainly hit Europa at some point. So scientists think chemicals might be lying at the bottom of Europa's ocean. They may have already created life—or may be about to.

You may wonder if light is also needed for life to form. Until recently, scientists thought that light was essential. But now places have been found on Earth that are in total blackness, such as caves several miles beneath the surface. And bacteria, primitive forms of life, have been seen there. So the lack of light in Europa's subsurface ocean doesn't automatically rule out life forming.

Needless to say, scientists want to learn more about Europa. They are continuing to study it closely.

86 其他行星上有生命吗？

自古以来，人们就对地球之外存在生命的想法着迷。直到最近，科学家们还认为地外生命只是一个美好的梦想。但现在他们开始找到可能形成生命的地方。1997年，他们发现了类日恒星附近存在行星的证据。行星是可能具备生命基本条件的地方。但科学家们现在认为，生命可能离我们更近，就在我们自己的太阳系里。

科学家们正在密切研究的一个地方是木卫二，它是木星的一颗卫星。太空探测器提供的证据表明，木卫二的表面下有一个巨大的海洋。探测器还让科学家们认为，木卫二的表面下有一个岩石核心，能释放出火山热。火山活动带来的水和热量是生命形成所需的两个基本条件。第三个条件是某些基本化学物质，比如碳、氧和氮。携带这些化学物质的彗星和陨石肯定在某个时候撞击过木卫二。所以科学家们认为，这些化学物质可能存在于木卫二海洋的底部。它们可能已经创造了生命——或者即将创造生命。

你可能会想，生命形成是否也需要光。直到最近，科学家们还认为光是必不可少的。但现在人们在地球上发现了完全黑暗的地方，比如地表以下数英里的洞穴。而且在那里发现了细菌——生命的原始形式。所以木卫二地下海洋缺乏光线，并不意味着一定不能形成生命。

不用说，科学家们想更多地了解木卫二。他们正在继续密切研究它。