科学英语：土卫六的大气与地球很相似

Scientists at UCL have observed how a widespread polar wind is driving gas from the atmosphere of Saturn's moon Titan. The team analysed data gathered over seven years by the international Cassini probe, and found that the interactions between Titan's atmosphere, and the solar magnetic field and radiation, create a wind of hydrocarbons2 and nitriles being blown away from its polar regions into space. This is very similar to the wind observed coming from the Earth's polar regions. Titan is a remarkable3 object in the Solar System. Like Earth and Venus, and unlike any other moon, it has a rocky surface and a thick atmosphere. It is the only object in the Solar System aside from the Earth to have rivers, rainfall and seas. It is bigger than the planet Mercury.

Thanks to these unique features, Titan has been studied more than any moon other than Earth's, including numerous fly-bys by the Cassini probe, as well as the Huygens lander which touched down in 2004. On board Cassini is an instrument partly designed at UCL, the Cassini Plasma4 Spectrometer (CAPS), which was used in this study.

"Titan's atmosphere is made up mainly of nitrogen and methane5, with 50% higher pressure at its surface than on Earth," said Andrew Coates (UCL Mullard Space Science Laboratory), who led the study. "Data from CAPS proved a few years ago that the top of Titan's atmosphere is losing about seven tonnes of hydrocarbons and nitriles every day, but didn't explain why this was happening. Our new study provides evidence for why this is happening."

Hydrocarbons are a category of molecules6 that includes methane, as well as other familiar substances including petrol, natural gas and bitumen7. Nitriles are molecules with nitrogen and carbon tightly bound together.

The new research, published today in the journal Geophysical Research Letters, explains that this atmospheric8 loss is driven by a polar wind powered by an interaction between sunlight, the solar magnetic field and the molecules present in the upper atmosphere.

"Although Titan is ten times further from the Sun than Earth is, its upper atmosphere is still bathed in light," says Coates. "When the light hits molecules in Titan's ionosphere, it ejects negatively charged electrons out of the hydrocarbon1 and nitrile molecules, leaving a positively9 charged particle behind. These electrons, known as photoelectrons, have a very specific energy of 24.1 electronvolts, which means they can be traced by the CAPS instrument, and easily distinguished10 from other electrons, as they propagate through the surrounding magnetic field."

词汇解析：

1 hydrocarbon

n.烃，碳氢化合物

参考例句：

During incomplete combustion some of the hydrocarbon fuel is cracked.在不完全的燃烧中，一些烃燃料裂解。

The hydrocarbon must be an alkene.这个碳氢化合物必定是烯烃。

2 hydrocarbons

n.碳氢化合物，烃( hydrocarbon的名词复数 )

参考例句：

Hydrocarbons (HC), like carbon monoxide, represent unburned and wasted fuel. 碳氢化合物(HC)像一氧化碳一样，为未燃尽的和被浪费掉的燃料。 来自英汉非文学 - 环境法 - 环境法

With this restricted frequency range it is not applicable to hydrocarbons. 这个较紧缩的频率范围不适用于烃类。 来自辞典例句

3 remarkable

adj.显著的，异常的，非凡的，值得注意的

参考例句：

She has made remarkable headway in her writing skills.她在写作技巧方面有了长足进步。

These cars are remarkable for the quietness of their engines.这些汽车因发动机没有噪音而不同凡响。

4 plasma

n.血浆，细胞质，乳清

参考例句：

Keep some blood plasma back for the serious cases.留一些血浆给重病号。

The plasma is the liquid portion of blood that is free of cells .血浆是血液的液体部分，不包含各种细胞。

5 methane

n.甲烷，沼气

参考例句：

The blast was caused by pockets of methane gas that ignited.爆炸是由数袋甲烷气体着火引起的。

Methane may have extraterrestrial significance.甲烷具有星际意义。

6 molecules

分子( molecule的名词复数 )

参考例句：

The structure of molecules can be seen under an electron microscope. 分子的结构可在电子显微镜下观察到。

Inside the reactor the large molecules are cracked into smaller molecules. 在反应堆里，大分子裂变为小分子。

7 bitumen

n.沥青

参考例句：

Bitumen paper can be burnt to gain energy.沥青纸可以焚烧以获得能量。

In fact,a speciality crude is suitable only for bitumen production.事实上，这种特性的原油只适宜于生产沥青。

8 atmospheric

adj.大气的，空气的；大气层的；大气所引起的

参考例句：

Sea surface temperatures and atmospheric circulation are strongly coupled.海洋表面温度与大气环流是密切相关的。

Clouds return radiant energy to the surface primarily via the atmospheric window.云主要通过大气窗区向地表辐射能量。

9 positively

adv.明确地，断然，坚决地；实在，确实

参考例句：

She was positively glowing with happiness.她满脸幸福。

The weather was positively poisonous.这天气着实讨厌。

10 distinguished

adj.卓越的，杰出的，著名的

参考例句：

Elephants are distinguished from other animals by their long noses.大象以其长长的鼻子显示出与其他动物的不同。

A banquet was given in honor of the distinguished guests.宴会是为了向贵宾们致敬而举行的。

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