Narrator: Listen to part of a lecture in an astronomy class.

旁白：听一个天文学相关的讲座。

Professor: OK. We've been discussing the planets in our solar system and how some of the ones farthest from the sun were discovered.

教授：好，我们一直在讨论我们太阳系中的行星，以及距离太阳最远的一些行星是如何被发现的

Well, today I'd like to turn to what are called exoplanets and how researchers detect them.

好，今天我要讲的是外行星，以及研究者是如何探测到他们的。

Maria?

玛利亚？

Student: Exoplanets are planets that orbit around a star other than our Sun, right?

学生：外行星是那些轨道绕着恒星而非绕着太阳的星球，对吧？

They are not in our solar system.

它们不在我们的太阳系中。

Professor: Right.

教授：对。

They have different... what are called "host stars".

它们有不同的……被称为“寄主星”的东西。

And the study of exoplanets has been getting more and more exciting.

关于外星的研究越来越刺激。

Hundreds of them have been discovered so far.

目前有数百个外行星被发现。

This is quite remarkable in view of the fact that the discovery of the first exoplanets was confirmed only in the mid-1990s.

鉴于第一颗系外行星的发现仅在20世纪90年代中期得到确认，这是非常了不起的

Now we're finding new ones every few weeks or so.

现在我们大约每隔几周就会发现一些新的外行星。

Student: So, uh, exactly why are we interested in these exoplanets anyway?

学生：那么，我们到底为什么对这些系外行星感兴趣呢？

Is it to see if there's life on them?

是要看看它们上面有没有生命吗？

Cuz it seem to me like the only exoplanets we ever hear about are gas giants like Jupiter and Saturn that couldn't possibly support carbon-based life.

因为我好像唯一听过的外行星就是像木星土星那样的气体行星，这些星球不可能支持以碳为基础的生命。

Professor: OK. Well, let's talk about that.

教授：好，我们来讨论一下。

First, as for discovering life.

首先，关于发现生命。

Well, I think that sort of discovery is pretty far in the future, but it is an eventual goal.

我想这类发现会是在遥远的未来，但这是最终的目标。

For now, the focus is on locating planets within a host star's so called "habitable zone", a zone that's a certain distance from its star ,because only planets within this zone could conceivably support carbon-based life.

现在，研究的核心是在寄主星所谓的“可居住区”内寻找行星，它通常距离它的寄主星有一段距离，因为只有“可居住区”内的行星才能支持以碳为基础的生命。

So, what would such a planet need?

那么，这样的行星需要什么呢？

Student: Water?

学生：水？

Professor: Yes, it need to be the right temperature to sustain liquid water.

教授：是的，它需要有适宜的温度以维持液态的水。

Student: And it would need to be a rocky planet, I mean, as opposed to a gas giant.

学生：并且它需要是多岩的行星，我的意思是，它不同于气体巨星。

Professor: OK, good. An Earth-like planet.

教授：好，很好，像地球一样的行星。

Now, as to that, there are some recently detected exoplanets that might actually be Earth-like.

现在，针对这个，最近有发现一些外行星确实可能跟地球比较像。

For example, there's a red dwarf star, that's what most stars are,urn... that's called Gliese 581.

例如，有一个红矮星，和大多数行星一样，它被叫做G581。

Gliese 581 is... well, it's a lot more interesting than that name makes it seem.

G581是……嗯，它实际比它名字给人的感觉要有趣得多。

This host star is considered a near neighbor of our solar system because it's only about 20 light years away.

这颗寄主星被认为是我们太阳系的近邻因为它距离太阳系只有20光年之遥。

It's pretty close by astronomical standards.

按照天文标准它很近。

And being a red dwarf star, it's small and relatively cool, at least compared with the Sun.

并且作为红矮星，它很小并且温度相对比较低，至少和太阳相比是这样的。

And researchers have discovered planets orbiting Gliese 581.

研究者发现有行星绕G581运行。

These exoplanets have been named, ready?

这些行星被命名为，准备好了吗？

Gliese 581 b, c, d, e, in alphabetical order of their discovery.

它们是G581 b, c, d, e, 根据他们的发现按照字母顺序排列。

Gliese 581 d and e are the planets I wanna focus on now.

G581 d 和e 是我现在重点讲解的行星。

See, in 2009, a group of researchers made an announcement.

在2009年，一组研究人员发表了一项声明。

These two exoplanets: Gliese 581 d and e do have some Earth-like qualities.

这两个外行星：G581 d 和e 有一些类似地球的特征。

Gliese 581 d had actually been discovered a couple of years earlier.

G581 d确实在早几年就发现了。

And when its orbit was originally calculated it was thought to be too far away from its host star to be warm enough to support a liquid ocean, let alone carbon-based life.

当它的轨道最初被计算出来的时候，它被认为离它的寄主星太远而不足够温暖以支持液体的水，更别说以碳为基础的生命了。

But then its orbit was recalculated and now we see that Gliese 581 d is within its host's habitable zone.

但在之后它的轨道被重新计算，现在我们可以看到G581 d是在它的寄主星的可居住区内的。

Student: So it might have an ocean?

学生：那么它上面可能有海洋？

Professor: Well, conceivably.

教授：嗯，是可信的。

See, Gliese 581 d weighs 7 times what Earth weighs and it's unlikely that it's made entirely of rocks because it's so massive.

你们看，G581 d的重量是地球重量的7倍，所以它不可能全部由岩石构成因为它太重了。

The researchers studying it said that it could have a rocky core, an ice layer, a large deep ocean and an atmosphere.

研究它的研究者说，它可能有个岩石核心，一个冰层，一个很大的深海和一个大气层。

OK, and there was another announcement along with the recalculated orbit of Gliese 581 d.

好，随着对G581 d的重新计算，还有另外一项声明。

That was the discovery of another planet in the system, Gliese 581 e.

那就是在这个行星体系中发现了另外一个行星，G581 e。

Compared with other exoplanets, its mass is quite small, only about twice that of Earth.

和其它外行星相比，它的质量很小，大约只是地球质量的两倍。

Student:So, is Gliese 581 e a more Earth-like planet?

学生：因此，G581 e 是更像地球的行星吗？

Professor: Well, we have to consider its orbit.

教授：嗯，我们得考虑到它的轨道。

Gliese 581 e orbits its host star in a much shorter period of time than the other planets in the system, meaning it's very close to the star, and therefore too hot for water, for an ocean.

G581 e 绕其寄主星运行的周期比这个行星系统中其它行星运行的周期短很多，这意味着它非常靠近寄主星，因此对于水、海洋而言，温度太高。

However, the fact that it's relatively close to the size of Earth, small, in astronomical terms, that was pretty exciting.

然而，它相对接近地球的大小，它很小它在天文学范畴看来很小，这是非常令人兴奋的。

It's impressive that we have the technology to detect it and it bodes well for future research.

令人印象深刻的是，我们有技术可以探测到它，这对未来的研究来说是个好兆头。

Who knows what we'll find the more we search.

谁知道我们做更多的研究会发现什么。