英语听力：自然百科 行星旅行：土星 Saturn—17

 These are just bold first steps on a journey that's just begun.

 

Even before the mission is over, Cassini has left a thirst for a return trip. 

 

Planetary explorer Jonathan Lunan and aeronautical¹ pioneer Julia Nod think they know the perfect way to do it---a robotic hot air balloon.

 

So where we are flying over now is very much like the Huygens landing site.

 

And I love to see those ravines on Titan though steep valleys where the methane² is flowing and covering all the hills very much like what we are seeing now.

 

The dream is to return to Titan and drop a robotic / balloon into the atmosphere. 

 

A radioisotope generator³ will provide the electrical power and the waste heat to give the balloon lift in the chilly⁴ atmosphere.

 

Titan has a dense⁵ atmosphere. It’s cold, the gravity is low, the winds are gentle, so ballooning is very easy.

 

I think this flight just makes the point so beautifully. Why a balloon is a wonderful way to explore Titan?

 

If you're over an interesting area, very easy to come down, maybe even land on the surface, lower instruments down.

 

One could cover with a robotic hot air balloon, the entire circumference⁶ of Titan in a space of perhaps six months.

 

You shouldn't think of Titan as a place just for robots. With a thick protected atmosphere and plenty of frozen water, Titan could be a more user-friendly destination for earthlings than Mars.

 

When humans do finally move out into the solar system, and I think Titan will be seen as a somewhat distant but very attractive place to go play.

 

You don't need a pressure suit on Titan, you don't have the feeling as the astronauts described, trying to work with a beachball between your arms

1 aeronautical   

adj.航空（学）的

参考例句：

• Many of the pilots were to achieve eminence in the aeronautical world. 这些飞行员中很多人将会在航空界声名显赫。 来自辞典例句
• The advent of aircraft brought with it aeronautical engineering. 宇宙飞船的问世导致了航天工程的出现。 来自辞典例句

2 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。

3 generator   

n.发电机，发生器

参考例句：

• All the while the giant generator poured out its power.巨大的发电机一刻不停地发出电力。
• This is an alternating current generator.这是一台交流发电机。

4 chilly   

adj.凉快的，寒冷的

参考例句：

• I feel chilly without a coat.我由于没有穿大衣而感到凉飕飕的。
• I grew chilly when the fire went out.炉火熄灭后，寒气逼人。

5 dense   

a.密集的，稠密的，浓密的；密度大的

参考例句：

• The general ambushed his troops in the dense woods. 将军把部队埋伏在浓密的树林里。
• The path was completely covered by the dense foliage. 小路被树叶厚厚地盖了一层。

6 circumference   

n.圆周，周长，圆周线

参考例句：

• It's a mile round the circumference of the field.运动场周长一英里。
• The diameter and the circumference of a circle correlate.圆的直径与圆周有相互关系。