About 100 days ago, we landed a two-ton（吨） SUV on the surface（表面） of another planet, on the surface of Mars. This is one of the first pictures we took there with our rover, looking out at Mount（山峰） Sharp. To me, it's I kind（种类） of cry a little bit, show couples, when I see this picture. Why Mars? And why do we look at these other planets? And part of it is to understand our own planet.

  What's the context for us? We live on this amazing planet, but Mars is a lot like Earth. It's similar in size. During the daytime（日间）, it can get up to about 70 degrees Fahrenheit（华氏温度计）. So it's so like Earth, but at the same time, you know, this is a barren（不生育的） landscape（风景）. You don't see any trees, you don't see any cactuses（[植]仙人掌） growing, anything like that.

  So today I want to tell you about the story of how we got from Earth to Mars and why it's so cool. So one of the things we start with is a blank sheet of paper. We knew from the previous（先的） missions（使命） in 2004, Spirit（ 精神） and Opportunity, there was water on Mars in the past. But, you know, what's the next step? We're looking for even more fundamental（基本的） level of what does it take to have life survive（幸免于）? And so to have that kind of, you know, knowledge and understanding, we have to carry a massive（厚重的） amount of instruments.

  We have to carry the kind of labs that people actually have whole rooms devoted（将…奉献） to on Earth inside of essentially（ 本质上） a small car. And what we did was we shrunk（收缩） it all down to something that weighs（ 称量） about as much as I do and then put it inside of this rover that weighs（ 称量）, you know, as much as your car does. And that rover is now on the surface of Mars. But it's so heavy. And so it kind of takes a special challenge（挑战） for us to make it all work and come together. So we look at our tool of, like（喜欢）, what do we have to land stuff（材料） on Mars?

  And one of the options is airbags. We've done it before. Airbags are pretty cool. They bounce（弹跳） around a lot. You could never put a human inside of an airbag because they would get squashed（镇压）. But the problem with airbags is the airbags that you see here, which landed the smaller rover, it's like 400 pounds, the entire（全部的） rover, were about the size of this room.

  So you can imagine the size of airbags we would take to land a two-ton rover on Mars. And then they have to be actually made out of materials that don't even exist today. So it would be some kind of exotic（异国情调的） material that we'd have to develop and may or may not work. So what about rockets（火箭）?