英语听力：自然百科 金星和水星旅行指南 Venus and Mercury-8

Reason/ you are going to go to Mercury as a travel destination would be this night sight view because it's going to be highly unique in the solar system. You have sodium thats atoms that are streaming off and giving enough to see yellow light, so you

英语听力：自然百科 金星和水星旅行指南 Venus and Mercury-6

After Messenger's 3 fly-bys, we've now mapped more than 90% of the planet. Taken from around 124 miles, these images are the clearest to date of Mercury. And it's not hard to spot a crater of epic proportions, the result of yet another Titanic collis

英语听力：自然百科 金星和水星旅行指南 Venus and Mercury-5

Mercury's core makes up about 60% of the planet by mass. It's about twice as big as earth. Why would it have such a huge core for such a small planet? Some people think there was a huge impact. Kind of stripped off a lot of the planet and now what we

英语听力：自然百科 金星和水星旅行指南 Venus and Mercury-4

Many aspects, like its geological past, are a mystery. But some things we do know, this lonely planet has a strange sense of keeping time. Once you arrive, you have to reset your watch for a time zone like no other. It has such an unusual orbit and r

英语听力：自然百科 金星和水星旅行指南 Venus and Mercury-3

Craters here stretch as far as the eye can see. Although no human has ever set foot on Mercury, we have a pretty good idea of what you would see. If you are walking around on the surface of Mercury, it will look outwardly a lot like the moon. When yo

英语听力：自然百科 行星旅行指南：火星 Mars—7

A test run before attempting the fuel hungry and risky trip to the planet below. Dreaming about Mars and actually going there are two very different things. Mars may be our neighbour, but 35 million miles to the closest point is still a very long way

英语听力：自然百科 行星旅行指南：火星 Mars—8

Before we take this giant leap, we need to be able to carry everything needed for a three-year -round trip with us. This is a much larger effort than getting to the moon. Its the Apollo mission on steroids. At this point we know at least as much as t

英语听力：自然百科 行星旅行指南：火星 Mars—9

Want to step outside to take in the scenery or pick up some rocks? As familiar as it might look beyond the port hole, Mars is dangerously alien. The upside is the low gravity will give you super jumping abilities, the down, the almost complete lack o

英语听力：自然百科 行星旅行指南：火星 Mars—10

But still be able to use your hands. Not only will you want to move your fingers, you want to move around. NASAs lunar electric rover is a prototype for future missions to the moon and Mars. Its part vehicle and part space suit. I can just picture be

英语听力：自然百科 行星旅行指南：火星 Mars—11

It was 119 Fahrenheit here yesterday; really, really, really hot day on Mars ever get up to about 30 Fahrenheit and at night it goes to more than 100 below. Martian deserts are both frozen and sun baked. With no Ozone layer, UV levels are so high tha

英语听力：自然百科 行星旅行指南：火星 Mars—12

Try the red planet for sight-seeing on an enormous scale. Thanks to our sharp-eyed spacecraft, Mars is opening up like never before. These are real landscapes that humans will one day marvel at in person. You know, if youre going to Mars, youre going

英语听力：自然百科 行星旅行指南：火星 Mars—13

You can make estimates of how much water had to have been flowing that carved these things, and you get numbers like 100, 200 Amazon rivers all cut loose at once, big, big amounts of waterfalls / across its surface. The other big attraction on Mars i

英语听力：自然百科 行星旅行指南：火星 Mars—14

When we reconstruct our imaginations, Mars are 3 billion years ago. We tend to make it like Earth, warm and clozzying, but it wasn't. Mars back in its wettest warmth face which probable like Earth today in its coldest regions. So I'm imagining a plac

英语听力：自然百科 行星旅行指南：火星 Mars—19

So in some ways, a voyage to Mars could be a voyage home. Our ancestors have made such bold trips before when we walked out of Africa, when we sailed over the horizon. If it is technically possible, our ships will head out again. We always want to se

英语听力：自然百科 行星旅行指南：火星 Mars—17

It is chemically impossible for methane to survive for long in the Martian atmosphere, so it must have been released recently. Now what makes methane? Cows make methane? Probably not cows. Oh, microbes, various sorts can release methane, there are a

英语听力：自然百科 行星旅行指南：火星 Mars—16

If we are looking for Martian bugs, we should search for life forms at least as tough and alien as this. Im looking at Mars in a point of view of a microbe. And as a microbe, I really need very, very tiny amount of water. I could probably live my ent

英语听力：自然百科 行星旅行指南：火星 Mars—15

If we have been wet, then we want to look for nutrients and food sources that could support microbes. The water ice is proof of a valuable resource for any life forms still clinging(附着) beneath the surface and for future travelers. We now know th

英语听力：自然百科 行星旅行指南：火星 Mars—18

There is no room to screw up on a trip like this, mental or otherwise. Once on Mars, you are likely to be stuck there for a year or more, waiting for a window of opportunity to ride home. And unlike a robot, the hopes and fears of the whole planet wi

英语听力：自然百科 行星旅行：土星 Saturn—1

No planet beats Saturn for jaw-dropping beauty. Saturn is the most photogenic planet in all the solar system. Some of the pictures are to die for. But the postcards only tell part of the story. Beauty is only skin deep. It really is rolling and seeth

英语听力：自然百科 行星旅行指南：火星 Mars—2

Its been said that the first person on Mars is alive somewhere on earth today. Imagine its you. What do you need to know? How much you get there? What should you pack? What are some of the must-see sights and what should you avoid? Think of this as y