# 第三册 Lesson 55 From the earth: Greetings 来自地球的问候

## 一、课文原文

Recent developments in astronomy have made it possible to detect planets in our own Milky Way and in other galaxies. This is a major achievement because, in relative terms, planets are very small and do not emit light. Finding planets is proving hard enough, but finding life on them will prove infinitely more difficult. The first question to answer is whether a planet can actually support life. In our own solar system, for example, Venus is far too hot and Mars is far too cold to support life. Only the Earth provides ideal conditions, and even here it has taken more than four billion years for plant and animal life to evolve.

Whether a planet can support life depends on the size and brightness of its star, that is its 'sun'. Imagine a star up to twenty times larger, brighter and hotter than our own sun. A planet would have to be a very long way from it to be capable of supporting life. Alternatively, if the star were small, the life-supporting planet would have to have a close orbit round it and also provide the perfect conditions for life forms to develop. But how would we find such a planet? At present, there is no telescope in existence that is capable of detecting the presence of life. The development of such a telescope will be one of the great astronomical projects of the twenty-first century.

It is impossible to look for life on another planet using earth-based telescopes. Our own warm atmosphere and the heat generated by the telescope would make it impossible to detect objects as small as planets. Even a telescope in orbit round the earth, like the very successful Hubble telescope, would not be suitable because of the dust particles in our solar system. A telescope would have to be as far away as the planet Jupiter to look for life in outer space, because the dust becomes thinner the further we travel towards the outer edges of our own solar system. Once we detected a planet, we would have to find a way of blotting out the light from its star, so that we would be able to 'see' the planet properly and analyse its atmosphere. In the first instance, we would be looking for plant life, rather than 'little green men'. The life forms most likely to develop on a planet would be bacteria. It is bacteria that have generated the oxygen we breathe on earth. For most of the earth's history they have been the only form of life on our planet. As Earth dwellers, we always cherish the hope that we will be visited by little green men and that we will be able to communicate with them. But this hope is always in the realms of science fiction. If we were able to discover lowly forms of life like bacteria on another planet, it would completely change our view of ourselves. As Daniel Goldin of NASA observed, 'Finding life elsewhere would change everything. No human endeavour or thought would be unchanged by it.'

## 二、重点词汇详解

| 单词 | 音标 | 词性 | 释义 | 用法说明 |
|------|------|------|------|----------|
| astronomy | /əˈstrɒnəmi/ | n. | 天文学 | — |
| detect | /dɪˈtekt/ | v. | 探测，发现 | detect planets 探测行星 |
| galaxy | /ˈɡæləksi/ | n. | 星系 | Milky Way galaxy 银河系 |
| emit | /ɪˈmɪt/ | v. | 发射，发出 | do not emit light 不发光 |
| infinitely | /ˈɪnfɪnɪtli/ | adv. | 无限地 | infinitely more difficult 无比困难 |
| evolve | /ɪˈvɒlv/ | v. | 进化 | life to evolve 生命进化 |
| orbit | /ˈɔːbɪt/ | n./v. | 轨道；绕轨道运行 | a close orbit 近轨道 |
| blot out | /blɒt aʊt/ | phr.v. | 遮住，遮蔽 | blot out the light 遮住光线 |
| bacteria | /bækˈtɪəriə/ | n. | 细菌 | 单数形式bacterium |
| generate | /ˈdʒenəreɪt/ | v. | 产生 | generate oxygen 产生氧气 |
| dweller | /ˈdwelə/ | n. | 居民 | Earth dwellers 地球居民 |
| cherish | /ˈtʃerɪʃ/ | v. | 珍视，怀抱 | cherish the hope 抱有希望 |
| realm | /relm/ | n. | 领域 | in the realms of science fiction 在科幻领域 |
| endeavour | /ɪnˈdevə/ | n. | 努力，事业 | human endeavour 人类的努力 |

## 三、语法知识点

### 1. it作形式主语/形式宾语

> **It** is impossible to look for life on another planet using earth-based telescopes.（形式主语）
> The development of such a telescope will make **it** possible to detect life.（形式宾语）

### 2. whether引导的主语从句

> **Whether a planet can support life** depends on the size and brightness of its star.

whether引导主语从句，不能用if替换。

### 3. 虚拟语气（与现在/将来相反）

> **If we were able to** discover lowly forms of life like bacteria on another planet, **it would** completely change our view of ourselves.

### 4. It is...that... 强调句

> **It is** bacteria **that** have generated the oxygen we breathe on earth.

强调主语bacteria。

### 5. the + 比较级..., the + 比较级...

> The dust becomes thinner **the further** we travel towards the outer edges of our own solar system.

= The further we travel, the thinner the dust becomes.

## 四、重点句型分析

### 1. capable of 有能力
> A telescope **capable of** detecting the presence of life.

capable of + 名词/动名词；注意：able to + 动词原形

### 2. in the first instance 首先
> **In the first instance**, we would be looking for plant life.

= first of all; primarily

### 3. rather than 而不是
> We would be looking for plant life, **rather than** 'little green men'.

### 4. 长难句分析
> Even a telescope in orbit round the earth, like the very successful Hubble telescope, would not be suitable because of the dust particles in our solar system.

主语：a telescope；in orbit round the earth作定语；like...为插入语举例；would not be suitable为主句谓语；because of引导原因状语。

## 五、课文翻译

天文学的最新发展使我们能够在银河系和其他星系中探测到行星。这是一项重大成就，因为相对而言，行星非常小，而且不发光。发现行星已经够难了，但在行星上发现生命将难上加难。首先要回答的问题是：一颗行星是否真的能维持生命。例如，在我们的太阳系中，金星太热，火星太冷，都无法维持生命。只有地球提供了理想的条件，而即使在这里，动植物生命的进化也花了超过四十亿年的时间。

一颗行星是否能维持生命取决于其恒星（即它的"太阳"）的大小和亮度。想象一颗比我们的太阳大、亮、热二十倍的恒星。行星必须离它很远才能维持生命。另一方面，如果恒星很小，维持生命的行星就必须在近轨道上运行，并提供生命形式发展的完美条件。但我们怎么找到这样的行星呢？目前，没有任何望远镜能够探测到生命的存在。开发这种望远镜将是21世纪伟大的天文项目之一。

使用地面望远镜在另一颗行星上寻找生命是不可能的。我们温暖的大气和望远镜产生的热量使我们无法探测到像行星那么小的物体。即使是绕地球运行的望远镜，如非常成功的哈勃望远镜，也不合适，因为我们太阳系中的尘埃粒子。望远镜必须远离到木星那么远才能在外太空寻找生命，因为我们越向太阳系外缘前进，尘埃就越稀薄。一旦我们探测到一颗行星，我们就必须找到一种方法遮住它恒星的光，这样我们就能正确地"看到"这颗行星并分析它的大气。首先，我们要寻找的是植物生命，而不是"小绿人"。行星上最可能发展出的生命形式是细菌。正是细菌产生了我们在地球上呼吸的氧气。在地球历史的大部分时间里，它们是我们星球上唯一的生命形式。作为地球居民，我们始终抱有被小绿人拜访并能够与他们交流的希望。但这种希望始终停留在科幻小说的领域。如果我们能够在另一颗行星上发现像细菌这样的低等生命形式，那将彻底改变我们对自己的看法。正如美国宇航局的丹尼尔·戈尔丁所观察到的："在别处发现生命将改变一切。人类的任何努力或思想都将因此而改变。"

## 六、语言点精讲

### 写作手法
1. **科学论证**：以科学事实为基础，逐步推理
2. **对比手法**：金星vs火星vs地球；现实vs科幻
3. **引用权威**：Daniel Goldin的引言增强说服力

### 文化背景
- Hubble（哈勃）太空望远镜于1990年发射，是天文学里程碑
- "小绿人"（little green men）是科幻小说中对外星人的经典形象
- Daniel Goldin是NASA前局长

## 七、课后练习要点

1. **强调句**：It is...that...
2. **虚拟语气**：与现在/将来相反
3. **主语从句**：whether引导的主语从句
4. **写作练习**：就人类寻找外星生命的话题写一篇科普文章

## 八、本课小结

本课讨论了天文学中寻找外星生命的科学问题和挑战。语法重点是强调句、虚拟语气、whether主语从句和the+比较级句型。词汇方面掌握astronomy、detect、emit、evolve、bacteria、endeavour等核心词。写作上学习科学论证和引用权威。