Wow, what a powerful question.  哇，多么掷地有声的问题！

You know, as a scientist -- planetary scientist -- we really didn't take that very seriously until recently. 作为一名科学家--行星科学家--我们很久以来都没有认真的考虑过这个问题。

Carl Sagan always said, "It takes extraordinary evidence for extraordinary claims." 卡尔·萨根常说，“非凡的断言需要有非凡的证据”。

And the claims of having life beyond Earth need to be definitive, 地球之外有生命的断言必须是明确的，

they need to be loud and they need to be everywhere for us to be able to believe it. 必须是响亮的，还需要证据充分，这样我们才会相信。

So how do we make this journey?  那么，我们要如何开始这段旅行呢？

What we decided to do is first look for those ingredients for life. 我们决定首先去寻找生命的基本要素。

The ingredients of life are: liquid water -- we have to have a solvent, can't be ice, has to be liquid. 生命的基本要素是：液态水--我们需要溶剂，不能是冰，必须是液态的。

We also have to have energy.  我们还需要能量。

We also have to have organic material -- things that make us up, 有机物质也是必不可少的--这些都是组成我们的生命体，

but also things that we need to consume.  以及供我们消耗的东西。

So we have to have these elements in environments for long periods of time for us to be able to be confident that life, 环境中必须长期存在这些元素，才会让我们相信：

in that moment when it starts, can spark and then grow and evolve. 生命在诞生的那一刻能够迸发出火花，并且能够成长和演变。

Well, I have to tell you that early in my career, when we looked at those three elements, 我必须坦白，在我职业生涯早期，当我们研究这三个要素时，

I didn't believe that they were beyond Earth in any length of time and for any real quantity. 我并不相信它们能在地球之外存在足够长的时间，或达到足够的规模。